leibniz’s conception of sensation (studia leibnitiana sonderheft 46)

Preprint / Appeared in: “Leibniz’s experimental philosophy”, ed. by Arnauld Pelletier (Studia Leibnitiana Sonderheft 46), 69-92

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Leibniz’s Conception of Sensation

By

Christian Barth (Berlin)

Sensation is a central feature of animal life. Leibniz’ view on sensation is arguably the

most elaborate one in early modern philosophy. I will argue that Leibniz holds a two-part

conception of the general category of sensation, which includes conscious as well as

unconscious acts. Moreover, Leibniz’ conception of conscious sensation consists of three

parts. The aim of this paper is to explain the components of these conceptions and their

interaction.

In the first section, I will shortly delineate the place the notion of sensation occupies within

the science Leibniz calls “psychologia”. In the second section, I will present and discuss three

main types of characterisation Leibniz gives of sensation. I will argue that Leibniz has

different targets in mind when formulating them: The first two characterisations concern

sensation in general, whereas the third one refers to conscious sensation. In sections three to

five, I will reconstruct in detail the components of Leibniz’ conception of the general category

of sensation and his conception of conscious sensation. Section six entails an account of a

fourth characterisation of sensation that connects conscious sensation to apperception. This

section also aims to show that sensory apperception should not be understood as an act of

reflexion.

1. The Significance of the Notion of Sensation for Psychologia

The concept of sensation1 is central to the discipline Leibniz calls “psychologia”.

Psychologia is a sub-discipline of philosophy. It examines primary substances, i.e. monads,

with regard to their powers and acts.2 Psychologia, in turn, is divided into three sub-

disciplines corresponding to the three types of monads: simple monads, souls of non-rational

animals3, and souls of rational animals. Leibniz uses special terms, which were common in his

1 Leibniz uses the French terms “sensation” and “sentiment” as well as the Latin term “sensio” in order to refer to sensations. 2 See C 526. 3 Leibniz uses the French term “animal” in order to refer to rational as well as non-rational animals and the term “bête” in order to refer to non-rational animals only (see, for instance, Principle of Nature and Grace (henceforth referred to by “PNG”) 4-5, Monadology (henceforth referred to by “M”) 14 and M 28-29). I will follow Leibniz and use the English term “animal” accordingly. Hence, I use “animal soul” in order to refer to the souls of rational as well as of non-rational animals.


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time, for the sub-discipline related to the souls of rational animals: These are the Latin term

“pneumatologia” and its French equivalent “pneumatique”.4

In PNG and other texts, Leibniz famously separates souls from simple monads in terms of

their power of sensation. Simple monads lack this power while the souls of non-rational as

well as of rational animals are in possession of it. It is, thus, the power of sensation that ties

the monads of non-rational and rational animals together and defines them as being souls in

contrast to simple monads. One must not conclude from this, however, that the respective acts

of sensation of non-rational and rational animals do not differ in any respect. Quite to the

contrary, only rational animals possess the power of thought and this power is not only active

in non-sensory, purely intellective thinking, but also when sensations occur. It follows that in

rational animals, sensations do not merely consist in non-conceptual representations of

objects, but are additionally accompanied by conceptual representations of these objects in

thought.

It seems that Leibniz conceives of the relation between the souls of non-rational and of

rational animals in terms of addition. The souls of rational animals are souls of non-rational

animals plus some additional factor X, namely a (complex) rational capacity that enables the

animal to reflect, reason, and recognise eternal truths.5 Accordingly, we need to distinguish in

Leibniz between a general notion of sensation, which applies to the souls of non-rational as

well as rational animals and helps to demarcate them from simple monads (I will use the term

“animal sensation” in order to express this general notion of sensation), and a specific notion

of rational sensation which only applies to rational souls. Again, the notion of rational

sensation should be understood in terms of addition, i.e., rational sensation is animal sensation

plus some additional factor due to an actualisation of rational capacities. Primarily, this

additional factor included in rational sensation consists in the application of conceptual

capacities that lead to the conceptualisation of the object that is non-conceptually represented

in an act of animal sensation. Hence, broadly put, rational sensation is conceptualised animal

sensation.

To sum up, Leibniz’ notion(s) of sensation play(s) three important roles in his psychologia:

4 See C 526 and A 6.6.56. 5 See PNG 4 and M 28-30. Leibniz is Aristotelian in the sense that he takes the souls of rational animals to be unities rather than composed of part souls (see GP VI 521). One might expect this contention to push Leibniz to hold that rationality is the unifying form rather than a specific additional capacity (or complex of capacities) of rational souls (for a recent discussion of this reading of the Aristotelian view see M. Boyle: “Essentially Rational Animals”, in: G. Abel / J. Conant (eds.), Rethinking Epistemology vol. 2, Berlin/Boston, 2012, 395-427). But this does not seem to be Leibniz’ position, since he seems to consider this rational capacity as an add-on to a sensory capacity that rational animals share with non-rational animals.


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(a) The notion of animal sensation demarcates the category of souls from the category of

simple monads.

(b) The notion of animal sensation clarifies the extent to which the souls of non-rational and

rational animals share cognitive powers.

(c) The specific notion of rational sensation defines one important respect in which rational

souls transcend the cognitive powers of the souls of non-rational animals.

These three roles define two essential tasks which must be fulfilled by an interpretation of

Leibniz’ conception of sensation:

First, one needs to clarify Leibniz’ characterisation of animal sensation as a non-

conceptual power pertaining to the souls of non-rational as well as rational animals. This

requires clarity concerning the conditions a perception must fulfil in order to to qualify as an

act of animal sensation. Moreover, these conditions must be spelled out within Leibniz’

broader metaphysics of inner-monadic activity.

Second, the distinctions Leibniz recognises between animal and rational sensation have to

be analysed. In particular, we need to explain how non-conceptual “images” contained in

animal sensation are conceptualised in rational sensation.

In this paper, I will confine myself to the first task. Hence, when I talk about sensation in

the following sections, I will refer to animal sensation that pertains to non-rational as well as

rational souls. My aim in this paper is to lay out the components Leibniz believes to

essentially belong to animal sensation and, furthermore, to conscious animal sensation in

particular. In the next section, I will present and comment on different characterisations of

sensation found in Leibniz’ writings. We will see that Leibniz holds a two-partite conception

of animal sensation and a tripartite conception of conscious animal sensation.

2. Three Characterisations of Sensation

In his writings, Leibniz presents us with three different characterisations of sensation. As it

turns out, these three characterisations are far from being unrelated. Instead, each subsequent

characterisation is more complex than the preceding one. I will argue that the third, most

complex characterisation of sensation is Leibniz’ conception of conscious sensation, whereas

the first two characterisations refer to sensation in general.


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2.1 Sensation as Distinct Perception

A first characterisation appeals to the notion of distinctness applied to perception. In a text

called A Specimen of Discoveries about Marvellous Secrets of a General Nature6, dated 1688,

Leibniz explains:

[A] It is also clear what perception, which belongs to all forms, is, namely the expression of many things in one,

which differs widely from expression in a mirror or in a corporeal organ, which is not truly one. But if the

perception is more distinct, it makes a sensation.7 (A 6.4.1625 / quoted from Leibniz. Philosophical Writings, ed.

by G. H. R. Parkinson, trans. by M. Morris and G. H. R. Parkinson, London/Toronto, 1973, p. 85; translation

modified; my highlighting)

According to this characterisation, being more distinct suffices for a perception to be a

sensation. This I will call the “distinctness condition” of sensation. It will reappear in the two

other kinds of characterisations, although sometimes expressed in modified form.

This first characterisation of sensation as being a comparatively distinct perception implies

that the property of being distinct is a gradual property. It allows for variation on a scale of

more or less. Furthermore, it implies that there is some degree of distinctness as a reference

level in comparison to which a perception needs to be more distinct in order to qualify as a

sensation. Hence, the distinctness condition raises two questions:

(a) What does it mean for a perception to be distinct to some degree?

(b) In comparison to what reference level of distinctness does a perception need to be more

distinct in order to qualify as a sensation?

Leibniz does not answer these questions in A Specimen of Discoveries. I will come back to

them in section three.

2.2 Sensation as Distinct Perception Accompanied by Memory

In the Monadology, we find an instance of a second kind of characterisation of sensation

that goes beyond the first one. In this second kind of characterisation, sensation is not only

described in terms of distinctness, but additionally in terms of memory. In M 19, Leibniz

famously says:

6 Specimen Inventorum De Admirandis Naturae Generalis Arcanis, A 6.4.1615-1630. 7 Patet etiam quid perceptio sit, quae omnibus formis competit, nempe expressio multorum in uno, quae longe differt ab expressione in speculo, vel in organo corporeo, quod vere unum non est. Quodsi perceptio sit distinctior, sensum facit.


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[B1] But, since sensation is something more than a simple perception, I think that the general name of monads

and entelechies is sufficient for simple substances which only have perceptions, and that we should only call

those substances souls where perception is more distinct and accompanied by memory.8 (GP VI 610 / quoted

from G. W. Leibniz. Philosophical Essays, trans. by R. Ariew and D. Garber, Indianapolis/Cambridge, 1989

(henceforth referred to by “AG”), p. 215; my highlighting)

The first condition of sensation Leibniz mentions here corresponds to the condition of

distinctness specified in [A]. In this case, however, it is presented only as one of two different

conditions for sensation. A perception needs to be more distinct, in order to form a sensation.

But Leibniz also mentions a second condition that does not occur in [A] at all. This condition

refers to memory. In order to constitute a sensation, a perception must be more distinct and

accompanied by memory.

In paragraph 4 of PNG we find a similar characterisation, which, again, mentions memory as

a second condition for sensation. Moreover, the first condition of distinctness is presented in

different form:

[B2] But when a monad has organs that are adjusted in such a way that, through them there is something

heightened and distinguished in the impressions they receive, and consequently something heightened and

distinguished in the perceptions that represent them (as, for example, when the rays of light are concentrated and

act with greater force because of the shape of the eye’s humors), then this may amount to sensation, that is, to a

perception accompanied by memory – a perception of which there remains an echo long enough to make itself

heard on occasion.9 (GP VI 599 / AG 208; translation modified; my highlighting)

In this passage, the distinctness condition is rephrased in terms of a perception in which

there is something heightened and distinguished. This rephrasing enables a clarification of

the distinctness condition we know from [A] and [B1] in terms of perceptions in which there

is something heightened and distinguished. I will follow this strategy of clarifying the

distinctness condition in section three.

Since [B1] and [B2] give us two rather than one condition for sensation, the question arises

how both conditions are connected. Are these conditions independent of each other or are they

8 [M]ais, comme le sentiment est quelque chose de plus qu'une simple perception, je consens, que le nom general de Monades et d'Entelechies suffise aux substances simples, qui n'auront que cela, et qu'on appelle Ames seulement celles, dont la perception est plus distincte et accompagnée de memoire. 9 Mais quand la Monade a des organes si ajustés, que par leur moyen il y a du relief et du distingué dans les impressions qu'ils reçoivent, et par consequent dans les perceptions qui les representent (comme, par exemple, lorsque par le moyen de la figure des humeurs des yeux, les rayons de la lumiere sont concentrés et agissent avec plus de force) cela peut aller jusqu'au sentiment, c'est à dire jusqu'à une perception accompagnée de mémoire, à savoir, dont un certain écho demeure longtemps pour se faire etendre dans l'occasion[.]


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interrelated? The latter is the correct answer.10 This can be derived from passages in which

Leibniz claims that only sufficiently distinct perceptions are accompanied by memory. For

instance, in PNG 4 Leibniz says with regard to animal memory:

It is true that animals are sometimes in the condition of simple living things, and their souls in the condition of

simple monads, namely when their perceptions are not sufficiently distinguished to be remembered, as happens

in a deep, dreamless sleep or in a fainting spell.11 (GP VI 599 / AG 208; translation modified; my highlighting)12

Hence, Leibniz claims that fulfilment of the memory condition depends on fulfilment of

the distinctness condition. The idea seems to be that fulfilling the distinctness condition

explains why the memory condition is fulfilled. If this is correct, the apparent tension between

the first and the second characterisation vanishes because the first can be understood as a

contracted presentation of the second characterisation. Given Leibniz’s assumption that a

more distinct perception – at least normally – enters memory, the first characterisation of

sensation in terms of fulfilment of the distinctness condition tacitly implies fulfilment of the

memory condition. It is only that Leibniz does not make this psychological fact explicit in the

first characterisation. In fact, however, Leibniz has the same conception of sensation in mind

in the first and the second characterisation.

2.3 Sensation as Distinct Perception accompanied by Memory and Attention

In two texts from 1710 we find an even more extensive characterisation of sensation that

mentions attention in addition to distinctness (which only mentioned in the first text, but

neglected in the second) and memory:

[C1] For sensation is perception that includes something distinct and is combined with attention and memory.13

(GP VII 330)

[C2] In the strict sense, “soul” is applied to a noble species of life, or sentient life, where there is not only the

faculty of perceiving, but in addition that of sensation, inasmuch, indeed, as attention and memory are joined to

10 In her dispute with Larry Jorgensen’s position, Alison Simmons argues extensively and persuasively for this claim (see A. Simmons: “Leibnizian Consciousness Reconsidered”, Studia Leibnitiana 43 2011/2 (published 2013), 196-215, esp. 209-212 (henceforth referred to by “Simmons Consciousness”)). 11 Il est vray que les Animaux sont quelques fois dans l'Etat de simples vivans, et leur Ames dans l'Etat de simples Monades, savoir quand leur perceptions ne sont pas assés distinguées, pour qu'on s'en puisse souvenir, comme il arrive dans un profond sommeil sans songes, ou dans un evanouissement. 12 See also GP VI 534, A 6.6.54, and A 6.6.112. 13 Sensio enim est perceptio, quae aliquid distincti involvit, et cum attentione et memoria conjuncta est.


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perception.14 (GP VII 529 / quoted from Leibniz. Selections, ed. by P. P. Wiener, New York, 1951, p. 505;

translation modified; my highlighting)

We find this even more complex characterisation of sensation implicitly in the earlier New

Essays on Human Understanding15 as well.16 According to this characterisation, sensation

does not only require distinct perception and memory, but also attention. Again, the attention

condition is not independent from the other two. As Leibniz points out in NE, “[m]emory is

needed for attention”17. So, we end up with the following tripartite account: For a perception

to be a sensation, the monad in question must attend to the perception (or, more precisely, to

the object represented by the perception). For a monad to attend to a perception, the

perception must be accompanied by memory. And for a perception to be accompanied by

memory, it needs to be distinct.

What is the relation between the first two characterisations of sensation in terms of the

distinctness and the memory condition, and the third characterisation, which additionally

alludes to attention? One might suggest that the difference between the characterisations

reveal a development in Leibniz’ view on sensation from a simple to a more complex account.

But this cannot be true since the second characterisation comes later (1714) than the third

(1710). Moreover, Leibniz already mentions attention as a condition of sensation in paragraph

33 of the Discourse on Metaphysics18 from 1686. There, Leibniz suggests that not only

heightened perception, but also attention is required for sensation:

We also see that the perceptions of our senses, even when they are clear, must necessarily contain some confused

sensation […] And this is almost like the confused murmur coming from the innumerable set of breaking waves

heard by those who approach the seashore. Now, if from several perceptions (which do not come together to

make one), there is none which stands out before the others and if they almost make impressions that are equally

strong or equally capable of determining the attention of the soul, the soul can only perceive them confusedly.19

(A 6.4.1582-1583 / AG 65; translation modified; my highlighting)

14 Stricte anima sumitur pro specie vitae nobiliore, seu pro vita sensitiva, ubi non nuda est facultas percipiendi, sed et praeterea sentiendi, quando nempe perceptioni adjungitur attentio et memoria. 15 Henceforth referred to by “NE”. 16 See A 6.6.54, A 6.6.113, and A 6.6.115. 17 See A 6.6.54. 18 Henceforth referred to by “DM”. 19 On voit aussi que les perceptions de nos sens, lors mêmes qu’elles sont claires, doivent necessairement contenir quelque sentiment confus […] Et c’est à peu près comme le murmure confus qu’entendent ceux qui approchent du rivage de la mer, vient de l’assemblage des repercussions des vagues innumerables. Or si de plusieurs perceptions (qui ne s’accordent point à en faire une) il n’y a aucune qui excelle par dessus les autres, et si elles font à peu près des impressions egalement fortes ou egalement capables de determiner l’attention de l’ame, elle ne s’en peut appercevoir que confusement.


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Again, we find the attention condition also mentioned next to the distinctness condition in

the following passage from 1694:

However, that does not mean it is not true that confused thoughts are in the end nothing else but a multitude of

thoughts which are in themselves like distinct ones, but which are so small that each by itself does not excite our

attention and does not accomplish distinguishing itself.20 (G IV 574–575 / quoted from Leibniz’s ‘New System’

and Associated Contemporary Texts, ed. and trans. by R. S. Woolhouse and R. Francks, Oxford, 1997, p. 140;

translation modified; my highlighting)

Since attention presupposes memory (which Leibniz neglects to make explicit in these

passages), both passages suggest that Leibniz holds the tripartite conception of sensation at

least from the mid 1680s onwards. This counts against the hypothesis of a development from

a simple to a more complex view.

A more convincing explanation appeals to the distinction between sensation in a general

sense, which includes unconscious mental states, and conscious sensation. Recall that in the

PNG 4 passage, Leibniz talks about “an echo” of a perception in memory, which “remains […

] long enough to make itself heard on occasion”. Since the perception does not make itself

heard now, but only on occasion, it seems that Leibniz has a perception in mind, which leaves

a trace in memory, but which is yet not conscious to the subject.21 What then is additionally

required for conscious sensation? The third characterisation gives an answer: Sensations turn

conscious, when the subject attends to them. The upshot of this is: The first two

characterisations concern sensation in a wide sense, which only requires distinctness and

storage in memory. In virtue of being stored in memory, the perception is a potential object

for attention, but, as a matter of fact, it does need to be attended to. The third characterisation

refers to conscious sensation, i.e., to sensations in the wide sense that actually are attended to.

In the next sections, I will address the distinctness condition, the memory condition, and

the attention condition in more detail.

3. The Distinctness Condition

The distinctness condition occurs in all three kinds of characterisations, but in different

forms. In [A] and [B1], Leibniz characterises sensation as a more distinct perception.

According to [B2], sensation involves perception in which there is something heightened and

20 Cependant il ne laisse pas d'estre vray que dans le fonds les pensées confuses ne sont autre chose qu'une multitude de pensées qui sont en elles mêmes comme les distinctes, mais qui sont si petites que chacune à part n'excite pas nostre attention et ne se fait point distinguer. 21 That Leibniz’s notion of sensation does not only denote conscious, but also unconscious mental states, is corroborated by further passages (see A 6.6.54, A 6.6.115, A 6.6.119, A 6.6.139, and A 6.6.239).


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distinguished. Finally, [C1] requires that sensation is a perception in which there is something

distinct. These different descriptions of the condition might give rise to the belief that Leibniz

wavers on the correct specification of the distinctness condition. I claim, however, that this is

not the case and that these different descriptions are only different expressions of the same

idea.

My strategy for vindicating this claim rests on the idea that the description of the

distinctness condition presented in [B2] is the most elaborate one, which is why the others

should be understood in light of it. In [B2], Leibniz presents an account of sensation in which

he connects the property of there being something heightened and distinguished in perception

to the property of there being something heightened and distinguished in corresponding

bodily impressions. In other words, Leibniz connects the inner-monadic act of sensation to the

corresponding physiological process. In doing so, he suggests that the notion of there being

something heightened and distinguished in a perception is to be understood in terms of the

notion of there being something heightened and distinguished in the bodily impression

represented by the perception. In the following, I will take this suggestion seriously.

Let us turn to the notion of being heightened as Leibniz applies it to perceptions. What

exactly is heightened in a perception? And what does it mean for it to be heightened? [B2]

provides us with materials for an answer. Leibniz points out that only living beings with sense

organs are capable of having perceptions in which there is something heightened and

distinguished:

But when a monad has organs that are adjusted in such a way that, through them there is something heightened

and distinguished in the impressions they receive, and consequently something heightened and distinguished in

the perceptions that represent them […].22 (GP VI 599 / AG 208; translation modified; my highlighting)

First, this passage shows that the notion of there being something heightened in something

applies to bodily impressions as well as to corresponding perceptions that represent those

bodily impressions. This gives us the opportunity to understand the notion of there being

something heightened in a perception in light of the notion of there being something

heightened in bodily impressions. Although Leibniz does not present an explicit

characterisation of the latter, passages suggest that the notion of there being something

heightened in a bodily impression refers to the force of the bodily impression. Thus, in PNG 4

Leibniz states that bodily impressions on the eyes are heightened because

22 Mais quand la Monade a des organes si ajustés, que par leur moyen il y a du relief et du distingué dans les impressions qu'ils reçoivent, et par consequent dans les perceptions qui les representent […].


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[…] the rays of light are concentrated and act with greater force because of the shape of the eye’s humors […].23

(GP VI 609 / AG 208; my highlighting)

Similarly, in M 25 Leibniz explains […] that nature has given heightened perceptions to animals, from the care she has taken to furnish them organs

that collect several rays of light or several waves of air, in order to make them more effectual by bringing them

together. There is something similar to this in odor, taste, and touch, and perhaps in many other senses which are

unknown to us.24 (GP VI 611 / AG 216; my highlighting)

As these passages reveal, saying that there is something heightened in bodily impressions

on sense organs is a way of describing the great force these impressions exhibit. What is

heightened in suchlike bodily impressions is their force; and for the impressions’ force to be

heightened just means that the force is great. At least partly responsible for the great force of

impressions on sense organs (compared to impressions on other regions of the body) is the

special design of these organs. Let us consider the case of the eye: Light rays impress

movements on the retina. Depending on the direction of movements of the impressing light

rays, the movements impressed either point in the same direction or not. Movements of light

rays that point in the same direction impress movements on the retina that likewise point in

the same direction. If the movements of light rays hitting neighbouring areas on the retina

point in the same direction, they impress movements on these neighbouring areas that also

point in the same direction. In virtue of pointing in the same direction, these movements do

not hinder each other, but add up to one strong movement. Correspondingly, their forces add

up to one strong force. Additionally, sense organs like the eyes are special in that they are

designed to concentrate impressions they receive. The result is that a larger amount of

impressed movements hit a smaller area of the retina to the effect that, if they point in the

same direction, they add up to an even stronger overall movement and to an even stronger

overall force. As Leibniz states, the design of the eye and its concentrating effect result in

impressed movements that possess greater force. This is the effect Leibniz is referring to

when he says that there is something heightened in impressions on sense organs.

Now, all bodily impressions on sense organs are, as impressions on the monad’s body in

general, represented by perceptions in the monad. The representation relation requires that the

23 […] lorsque par le moyen de la figure des humeurs des yeux, les rayons de la lumiere sont concentrés et agissent avec plus de force […]. 24 […] que la Nature a donné des perceptions relevées aux animaux par les soins, qu'elle a pris de leur fournir des organes, qui ramassent plusieurs rayons de lumiere ou plusieurs undulations de l'air pour les faire avoir plus d'efficace par leur union. Il y a quelque chose d'approchant dans l'odeur, dans le goût et dans l'attouchement et peutêtre dans quantité d'autres sens, qui nous sont inconnus.


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perception “mirrors” the features of the bodily impression in the sense of a structure-

preserving relation.25 The structure-preserving nature of representation entails that there is

something heightened in the representing perception. Of course, what is being heightened in a

perception cannot be a bodily force. However, in order for the representation relation to

obtain, the perception needs to involve some feature that shares the formal characteristics of

bodily force and, for example, allows for more or less on a quantitative scale as bodily force

does. Let me call this feature the “strength” of a perception.26 A perception represents the

force of a bodily impression in virtue of its strength. Hence, a perception’s property of

involving something heightened turns out to be the property of having heightened, i.e. great,

strength.27

Before we can discuss Leibniz’ notions of being distinguished and of being distinct, we

need to obtain clarity about two observations concerning Leibniz’ use of the term

“heightened”. First, in DM 33 and PNG 13 Leibniz talks of heightened perceptions rather than

of there being something heightened in perceptions. However, this difference in wording

should not disturb us. Whenever Leibniz talks of heightened perceptions as he does in DM 33

and PNG 13, we should understand him as using an abbreviation for saying that there is

something heightened, namely heightened strength, in the perception. The second observation

requires longer treatment. In passages such as DM 33 and PNG 13 Leibniz characterises

perceptions as heightened in an absolute sense. In other passages, however, he characterises

them in some non-absolute, comparative sense as “slightly heightened”28 and “more

heightened”29. Since these characterisations of perceptions occur in passages in which Leibniz

is concerned with characterising sensation, we are confronted with a further version of the

distinctness condition. Rather than saying that the distinctness condition requires heightened

perception, Leibniz maintains in these passages that it requires more heightened perception.

And on a closer look, even [B2] seems to involve an implicit appeal to comparative

heightenedness - an aspect of this passage I have neglected so far. This is the case because

Leibniz says that if there is something heightened and distinguished in a perception, this might

amount to sensation. The modal term “might” indicates that not every degree of

heightenedness suffices for sensation, but only one that is sufficiently high. The comparative

use of the term “heightened” implies that the property of being heightened is gradual and

25 See C. Swoyer: “Leibnizian Expression”, in: Journal of the History of Philosophy 33/1 (1995), pp. 65-99. 26 I will not investigate here any further the ontology of perceptual strength. But it seems plausible that the strength of perceptions is related to the strength of appetites attached to these perceptions. 27 Cp. GP II 90-91, A 6.6.54, A 6.6.115, A 6.6.134, and M 25. 28 A 6.6.112. 29 A 6.6.139.


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allows for more or less. This should not come as a surprise since what is heightened in a

perception is the perception’s strength, and the perception’s strength is a gradual property that

allows for more and less. The comparative use of “heightened” additionally implies a

reference level of being heightened with regard to which a perception can be described as

slightly or more heightened. As passages indicate, this reference level is set by the

heightenedness of other co-occurring perceptions.30 In the context of sensation, these co-

occurring perceptions represent less strong impressions on parts of the body that do not have

the amplifying effect, which sense organs have. I will call these perceptions “non-amplified

background perceptions”. In NE Leibniz says that “there are countless slightly heightened

perceptions, which are not sufficiently distinguished for one to apperceive or to remember

them”31. According to this passage, the distinctness condition of sensation requires

heightenedness to a sufficient degree - a degree that leads to sufficient distinguishedness -

rather than heightenedness of any degree. In other words: Sensation requires perception

whose strength is greater than some level of strength, where this threshold is significantly

above the strength of co-occurring non-amplified background perceptions.32

Let us now come back to the absolute and the comparative version of the distinctness

condition. I would like to suggest that both conditions are closely related and amount to the

same thing, i.e., they are just alternative ways of expressing the same condition. When

Leibniz says that sensation requires heightened perception (i.e., perception whose strength is

heightened), he means that it requires perception whose strength goes beyond some (possibly

context-dependent) level (which is significantly above the strength of co-occurring non-

amplified background perceptions). And when Leibniz says that sensation requires more

heightened perception, he means that it requires perception whose strength is more heightened

than this level. Both versions of the distinctness condition are equivalent.

After having clarified the property of there being something heightened in a perception, let

us now turn to the property of there being something distinguished in a perception, which is

also mentioned in [B2]. The order of phrasing in [B2] suggests that there being something

distinguished in a perception is to be understood in terms of there being something heightened

30 See DM 33 and GP VI 534. 31 A 6.6.112 / quoted from G. W. Leibniz: New Essay on Human Understanding, trans. and ed. by P. Remnant and J. Bennett, Cambridge, 1996 (henceforth referred to by “RB”), p. 112; translation modified; my highlighting. 32 There remains the question as to what determines the required level of strength. Is the level dependent on contextual factors? Or is it context-insensitive? Leibniz does not tell us much beyond the fact that he assumes some such level of strength to exist. From his characterisations of sensation we can distil, however, two further features of this level: First, the amplifying effect of sense organs can suffice to lift the corresponding perceptions above the required level. Second, impressions on the body (and the corresponding perceptions) that are not amplified by sense organs remain below the level despite the fact that there is (small) variation among them with regard to strength as well.


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in it.33 Given that this is correct, a natural way of understanding [B2] tells us that what is

distinguished in a heightened perception is the very feature that is heightened in it, namely its

strength. The perception’s strength is distinguished because it is heightened and, thus, greater

than the level required for sensation. What it is distinguished from is the strength of co-

occurring perceptions, which remain below the level required for sensation. If this account is

correct, then applying the term “heightened” directly to perceptions rather than to something

in perceptions should pass on to the use of “distinguished”. Several passages show that this is,

indeed, the case.34 Again, we should understand Leibniz’ application of “distinguished” to

perceptions as an abbreviation for saying that there is something distinguished in the

perceptions, namely their strength. Furthermore, if the proposed account is correct, one should

observe an absolute as well as a comparative use of “distinguished” in Leibniz’ writings.35

This is vindicated by many passages. In the context of clarifying sensation, Leibniz says that

perceptions are “more distinguished”36, “less distinguished”37, and “insufficiently

distinguished”38. As in the case of the comparative use of “heightened”, the comparison in

question refers to some level of strength required for sensation.

Finally, let us turn to the notion of distinctness Leibniz applies in his characterisations of

sensation.39 Again, in Leibniz’ use of “distinct” in this context we find all variations we have

already found in his use of the terms “heightened” and “distinguished”. Leibniz speaks of

something distinct in perception (see [C2]) and of distinct perception (see PNG 13); and he

applies “distinct” to (something in) perception in an absolute ([C2]) as well as a comparative

sense (see [A] and [B1]). I would like to suggest that we should understand Leibniz’ use of

“distinct” in this context as being equivalent to his use of “distinguished”. Hence, “distinct

perception” would, again, refer to a perception with strength above the level required for

sensation. The same holds true, I suggest, of Leibniz’ talk of “more distinct perception” and

“there being something distinct in perception”.

33 Cp. R. Glauser / L. Berchielli: “Sensations and Ideas of Sensible Qualities in Leibniz”, in: M Carrara, A. M. Nunziante, and G. Tomasi (eds.), Individuals, Minds and Bodies: Themes from Leibniz, Studia Leibnitiana Sonderheft 32, Wiesbaden, 2004, p. 241. 34 See A 6.6.162, GP III 307, and M 20. 35 As we should expect, we find a comparative use of “distinguished” also with regard to bodily impression (see A 6.6.117). 36 A 6.6.173 and A 6.6.201. 37 GP IV 563. 38 A 6.6.112 and GP VI 600. 39 As has been recognised by many scholars, Leibniz applies two different notions of distinctness to ideas and perceptions respectively. Leibniz defines the distinctness of ideas in terms of definability (with the exception of simple ideas that are distinct, yet not definable). However, the distinctness of ideas must be sharply distinguished from the distinctness of perceptions since the latter is not a matter of definability, but of strength.


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In sum, my suggestion is that Leibniz’ different uses of “distinct”, “distinguished”, and

“heightened” in the context of sensation all relate to the idea of perception with great strength,

i.e., with strength above the level of strength required for sensation. The different

formulations of the distinctness condition are only different expressions of this same

requirement for sensation.

4. The Memory Condition

4.1. Kinds of Memory

From [B1], [B2], [C1], and [C2] we learn that sensation does not only require distinct

perception, but also memory. Therefore, in order to understand the role of memory in

sensation, we must obtain clarity about Leibniz’ notion of memory. Leibniz does not elaborate

on this condition in these passages, which is why me must turn to other passages for

clarification.

Leibniz claims that each and every occurring perception leaves a trace in a monad.40 This

doctrine of traces must be strictly distinguished from Leibniz’s notion of memory. Whereas

traces are not accessible by the subject and cannot give rise to acts of remembering, memory

contains “residues” from earlier perceptions, which can give rise to such acts.41 In this section,

I will mainly be concerned with memory, not with the doctrine of traces, since only the

former is relevant for sensation.

Let us start with a conceptual distinction. In general, the term “memory” commonly refers

to two different items:

(a) When saying, for instance, that someone has long memory, one refers to memory as a

capacity. Memory as a capacity, in turn, includes two different abilities: the ability to store

contents and the ability to reactivate them by acts of remembering.

(b) When saying, for instance, that one has a lively memory of one’s recent holiday, one

refers to an individual act of remembering what happened during that last holiday, i.e., one

refers to memory as an act. An act of memory is the result of an actualisation of the second

ability just mentioned, namely the ability to reactivate stored content.

40 See, for instance, DM 8 and A 6.6.113. 41 See DM 8, A 6.6.6, A 6.6.55, A 6.6.114-115, and A 6.6.239. In DM 9 Leibniz claims that the doctrine of traces follows from his definition of substance in terms of complete individual concept.


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Leibniz is well aware of the distinction between memory as a capacity and memory as an

act. They both occur prominently in his writings.42 I will discuss Leibniz’ view of both kinds

of memory in turn and begin with memory as a capacity. Leibniz uses the Latin term

“memoria” and the French term “memoire” mainly (though not exclusively43) in the sense of

capacity. For instance, in NE Leibniz says that memory (memoire) stores our knowledge: But I am surprised that it has not occurred to you [sc. Philalethes] that we know an infinity of things which we

do not apperceive all the time, even when we need them; it is the function of memory to store them, and of

reminiscence to put them before us again, which it does often – but not always – when there is need for it to do

so.44 (A 6.6.76-77 / RB 76-77; translation modified; my highlighting)

Memory is here described as a capacity to store knowledge or, more general, content.

Leibniz also mentions reminiscence as a capacity to reactivate stored contents. Hence, in this

passage Leibniz draws the distinction between the two capacities mentioned earlier, namely

the distinction between a capacity to store and a capacity to reactivate stored content (“to put

them before us again”). Although Leibniz restricts the term “memoire” in this passage to the

former capacity, he is not consistent in doing so and often uses the term and its Latin

equivalent in order to refer to both capacities at once. I will do the same in my usage of the

term “memory”.

What does memory in the sense of a complex capacity to store and to reactivate content

consist in? Although Leibniz frequently uses the vocabulary of faculty psychology, ultimately

all talk of faculties has to give way to talk of perception and appetite because, as we know, in

monads we only find a primitive active force modified by appetites and perceptions. And,

indeed, in NE, Leibniz explains memory in terms of singular dispositions rather than one

general capacity:

One needs a somewhat more distinct explanation of what this faculty [of memory; CB] consists in and how it is

exercised: that would show that there are dispositions which are the remains of past impressions, in the soul as

well as in the body, but which we apperceive only when the memory finds an occasion for doing so. And if

nothing were left of past thoughts the moment we ceased to think of them, it would be impossible to explain how

42 For an extensive discussion of memory in Leibniz see also L. Jorgensen: “Leibniz on Memory and Consciousness”, in: British Journal for the History of Philosophy 19/5 (2011), pp. 887–916. 43 See A 6.4.1394. 44 Mais je suis etonné comment il ne vous est pas venu dans la pensée, que nous avons une infinité de connoissances, dont nous ne nous appercevons pas tousjours, pas même lorsque nous en avons besoin, c'est à la memoire de les garder, et à la reminiscence de nous les representer, comme elle fait souvent au besoin, mais non pas tousjours.


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we could keep the memory of them; to resort to a bare faculty to do the work is to talk unintelligibly.45 (A

6.6.140 / RB 140; translation modified; my highlighting)

In the final analysis we do not find a general capacity of memory as a separate entity

within souls, but only dispositions that are remain of earlier perceptions. They are dispositions

to specific acts of remembering. In the following, I will call them “memory dispositions”.

Since Leibniz rejects the idea of purely passive dispositions46, memory dispositions are to be

understood as active strivings to realise acts of remembering. Memory dispositions,

considered as strivings, form a subclass of appetites.

When turning to memory as an act, we see that Leibniz defines two kinds of acts of

remembering in the NE:

I shall say that it is sensation when one apperceives an external object, and that the reminiscence of it [= the

sensation; CB] is the repetition <of it [= the sensation; CB]> without the return of the object; but when one

knows that one has had it [= the sensation; CB] before, it is souvenir.47 (A 6.6.161 / RB 161; translation

modified)

As Leibniz explains, acts of reminiscence are recurrences of former sensations.48 Of

course, Leibniz does not mean that the numerically identical act of sensation recurs. This is

impossible. Rather, an act of reminiscence is a perception that is numerically different from

the original sensation. It only contains the same content as the original sensation.

Leibniz’ notion of reminiscence as an act closely corresponds to his conception of memory

as a capacity, i.e., as memory dispositions. An act of reminiscence is an actualisation of a

memory disposition. This is why Leibniz calls the capacity to recall stored content in the

quotation above (from A 6.6.77) “reminiscence”.

Two further comments on Leibniz’ notion of reminiscence are in order:

45 Il faudroit expliquer un peu plus distinctement, en quoy consiste cette faculté et comment elle s’exerce, et cela feroit connoistre qu’il y a des dispositions qui sont des restes des impressions passées dans l’ame aussi bien que dans le corps, mais dont on ne s’appercoit que lorsque la memoire en trouve quelque occasion. Et si rien ne restoit des pensées passées aussi tost qu’on n’y pense plus, il ne seroit point possible d’expliquer comment on en peut garder le souvenir; et recourir pour cela à cette faculté nue c’est ne rien dire d’intelligible. 46 See A 6.6.110. 47 Je dirai donc, que c’st Sensation lorsqu’on s’appercoit d’un objet externe, que la Reminiscence en est la repetition sans que l’objet revienne, mais quand on scait qu’on l’a eue, c’est souvenir. 48 For reminiscence in the technical sense see also A 6.6.271 and GP III 299. Unfortunately, Leibniz’ use of the term “reminiscence” at least in writings before NE (and even in NE itself in sections previous to the technical definition of reminiscence) do not comply with this definition. In A 6.6.6 Leibniz uses “reminiscence” in order to refer to the doctrine of traces. In A 6.4.1624 he uses “reminiscentia”, in A 6.6.10 and A 6.6.77 he uses “reminiscence” in the technical sense of “souvenir”.


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First, in the last quotation Leibniz characterises sensation as apperception of outer objects

(we will come back to this definition in section six). Since Leibniz uses the term

“apperception” and its cognates to distinguish conscious from non-conscious acts and since he

characterises acts of reminiscence in relation to sensations, it is obvious that acts of

reminiscence are supposed to be conscious acts. This claim finds additional support in the

observation that Leibniz explains animal and human associative reasoning, which are

supposed to be conscious processes, by an appeal to the notion of reminiscence.49

Accordingly, memory dispositions related to reminiscence consist in dispositions to realise

conscious acts of remembering.

Second, although Leibniz introduces the notion of reminiscence in relation to sensations,

we are not forced to and, indeed, should not conclude that acts of reminiscence are in all cases

rememberings of sensory content. In the quoted passage, Leibniz characterises reminiscence

in relation to acts of sensation. But he does not claim that only content of sensations can be

reactivated in acts of reminiscence.50 By contrast, we should assume that intellectual content

can also be reactivated by acts of reminiscence. For instance, suchlike acts of reminiscence

are required for fast sequences of habitualised reasoning in which premises are drawn from

memory.

In the quoted passage from A 6.6.161 Leibniz also defines a second notion of

remembering, namely the notion of souvenir. Acts of souvenir include an act of reminiscence,

but they are not merely acts of reminiscence. Additionally, they include knowledge of the fact

that one has entertained the same content before. In the case of souvenir, then, stored content

is not only reactivated, but the remembering monad conceives of it or, at least, can51 conceive

of it as content it has consciously entertained before, i.e., as content it remembers. Hence, acts

of souvenir have content of the form “I remember X” or “I remember that p” or, at least, they

are acts of remembering with regard to which the monad has the capacity of ascribing them to

itself as acts of remembering something it has entertained before. Again, acts of souvenir are

conscious acts and they are not restricted to remembering contents of sensations. Acts of

souvenir of intellectual content are also possible.

49 See 6.6.271. 50 Leibniz’ focus on sensation is due to the context of this passage. In the quoted passage Leibniz answers Philalethes’ definitions of psychological notions and Philalethes defines reminiscence in relation to sensation (see A 6.6.160). 51 I am cautious here and insert a “can”, because at A 6.6.161 Leibniz speaks of “knowing” that has had the sensation before and it is not clear whether Leibniz has occurring knowledge in mind or knowledge in some dispositional sense, which does not require an occurring of knowing.


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After having clarified the different types of memory Leibniz distinguishes, it is time to see

which types of memory he assigns to which type of monad:

(a) According to the doctrine of traces, all monads possess traces of all their former

perceptions.

(b) Since only animals are capable of conscious acts, they alone possess memory and acts of

reminiscence. Leibniz implies that animals are capable of acts of reminiscence in his

description of their associative reasoning.52

(c) Since non-rational animals do not possess the idea of the self53, they cannot have acts of

souvenir. Hence, only rational souls are capable of them.

To sum up, whereas all monads have traces of all their former perceptions, only the souls

of animals additionally have memory, i.e., a storage of contents to which they have access.

Moreover, whereas non-rational animals are only capable of reminiscence, rational animals

are additionally capable of souvenir.

4.2. The Role of Memory in Sensation

After this tour de force through Leibniz’ theory of memory, let us come back to the

question of sensation. We saw that memory is one of the necessary conditions for sensation.

But in what way does sensation involve memory? And what kind of memory does it involve?

In [B2], Leibniz seems to express the view that a perception can only be a sensation if it is

stored in memory. This reading is suggested by Leibniz’ talk of a remaining echo one might

come to remember consciously at some later point in time (“make itself heard in occasion”).

Hence, Leibniz seems to say that a sensation is a distinct perception of which a disposition to

conscious memory remains.

When it comes to conscious sensation, however, mere storage in memory cannot be the

whole story. Recall that sensations turn conscious in virtue of being attended to. Attention, in

turn, requires memory, as Leibniz says. Surely, it is not mere storage of content in memory

that Leibniz alludes to here. Instead, we need acts of remembering as objects of attention and,

thus, as being constitutive of conscious sensation. Moreover, since not only rational animals

52 See A 6.6.272. This passage comes after Leibniz’ technical definition of “reminiscence” at A 6.6.161. Hence, we have to understand the term here in its technical sense. 53 See DM 34.


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but animals in general are capable of conscious sensation, the act of memory in question

cannot be an act of souvenir. Instead, it must be an act of reminiscence. This means that it is

an act of repeating the content of the original distinct perception. In contrast to acts of

reminiscence, which repeat the content of truly past sensations, the act of reminiscence

constitutive of conscious sensation is immediate54. It has the effect of making the repeated

content available for being attended to.55 Because the original content is repeated, attention

can get directed towards it.

5. Attention

The question of attention in sensation is a difficult one. The reason for this is that Leibniz

often claims attention to be essential for sensation, but does not elaborate on this claim.

However, there is one thing we can be sure of: For Leibniz, attention in general requires

memory. This he explicitly claims in NE.56 It seems that this claim rests on the idea that a

monad can only attend to a representational content if this content is present for longer than

just a moment. But in the case of sensation, for instance, the representational content is in

constant flux and fleeting. Hence, in order to be able to attend to the representational content,

it needs to be stored in memory and, indeed, remembered in order to retrieve the content and

direct one’s attention towards it. I have called this act of remembering an act of immediate

content-repetition. But a mere repetition of content as such does not constitute an act of

attending to the represented object. Something more is required. But what needs to be added

to an act of immediate content-repetition in order to for an act of attending to a

representational content to occur?

In order to answer this question, we need to turn to Leibniz’ characterisations of attention.

In NE Leibniz states:

We are attentive to objects which we distinguish from and prefer to others.57 (A 6.6.161 / RB 161, translation

modified)

54 One has to keep in mind, however, that there is necessarily some short time gap between the occurrence of the original distinct perception and the act of immediate content-repetition. This is due to the fact that transferring the original impression on the sense organ to the brain, where the organ of memory is located, takes time. 55 The important role of acts of immediate memory in the constitution of sensation is also highlighted by Martha Bolton (see M. Bolton: “Leibniz’s Theory of Cognition”, in: B. Look (ed.), The Continuum Compendium to Leibniz, London/New York, 2011 (henceforth referred to by “Bolton”), pp. 146-147). 56 See A 6.6.54. 57 Nous avons de l’Attention aux objets que nous distinguons et preferons aux autres.


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According to my reading of this passage, Leibniz here defines acts of attending to a

particular object in terms of two individually necessary and jointly sufficient conditions:

(a) In order to be attentive to a particular object, the subject must distinguish this object from

other objects.

(b) In order to be attentive to a particular object, the subject must prefer this object to other

objects.

Now, the wording and context of this definition suggest that what Leibniz is primarily

concerned with here is voluntary attention.58 But voluntary attention to an object is surely not

the kind of attention Leibniz has in mind with regard to the attention condition of sensation.

Instead, voluntary attention to sensible objects presupposes sensation of these objects. Before

I can attend to the burglar creeping around in the garden, I must first look into the garden and

see what is there. Instead of voluntary attention, it is involuntary attention to objects, which

are not yet conscious, that plays a constitutive role in sensation. Accordingly, we are not

allowed to immediately apply the mentioned definition of attention to the case of sensation.

Yet, it is a natural to assume that we can get a grip on Leibniz’ conception of involuntary

attention by properly varying the definition for voluntary attention. Let us consider both

conditions in turn.

The first condition says that voluntary attention to an object requires the subject to

distinguish the object from other objects. It seems that this condition requires the subject to

actively distinguish the object in question from other objects. The subject is doing the

distinguishing and this activity is subject to her voluntary control. Involuntary attention,

however, must not rely on any voluntary activity of distinguishing. Somehow the object

attended to must be distinguished from other objects without the subject doing the

distinguishing in some voluntary sense. But this variation on the first condition fits well with

the fact that conscious sensation requires an act of immediate content repetition. We can say

that an object of involuntary attention required for conscious sensation is distinguished from

all the other objects, which were represented by insufficiently distinguished perceptions that

only left traces, by the very fact that it is the object of an act of content repetition. Hence, we

58 The wording of the definition indicates this because the defining clause seems to refer to voluntary acts of distinguishing an object from and giving it preference to other objects. Furthermore, subsequent to this characterisation Leibniz defines special forms of “being attentive to an object”, namely “consideration”, “contemplation”, and “study”. All three special forms consist in acts of voluntarily directing one’s attention towards some subject matter of which one is already conscious of.


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can capture the first condition of involuntary attention, which is constitutive of conscious

sensation, as follows:

In order to involuntarily attend to a particular object of sensation, an act of immediate

content repetition must occur that represents this object and, thereby, distinguishes this object

from all other perceived objects, which are not represented by an act of immediate content

repetition.

Next, let us turn to the second condition of attention. In the case of attention constitutive of

sensation, we do not voluntarily prefer an object to other objects. But what exactly does it

mean that an object is involuntarily attended to? A promising interpretation of this condition

understands Leibniz as referring to appetites. In order to substantiate this suggestion, it is

helpful to turn to a second definition of attention from the period of 1702 to 1704,59 where

Leibniz states: “Attention is thought accompanied by a desire for knowing”60 (C 493). The

definition suggests that attention essentially involves a desire aiming at knowledge. Let us call

appetites that aim at knowledge “cognitive appetites”. The passage C 493 suggests then that

we should understand attention, which is required for conscious sensation, in terms of

cognitive appetites. Since attention requires memory, the cognitive appetite must be taken to

refer to the special act of remembering that I have characterised as an act of immediate

content-repetition. Simply put, the cognitive appetite “asks”: What object are we sensing and

what features does it possess?

In sum, then, the attention condition of conscious sensation contains two part conditions:

(a) It requires an act of immediate content repetition, which represents the object in question.

(b) A cognitive appetite must occur that aims at knowledge about the object represented by

the act of content repetition.

In sum, then, conscious sensation of an object O requires a distinguished perception of O

that represents a forceful impression on the sense organ and which leaves a memory

59 Cf. Bolton, 156. In this definition Leibniz specifies attention in relation to thoughts. Since sensations are not thoughts in the technical sense of propositionally contentful states, one might think that the given definition is irrelevant for the question of sensation. Note, however, that Leibniz uses the term “cogitatio” ambiguously, applying it in reference to propositional thoughts only (narrow sense) as well as to perceptions in general (wide sense). Leibniz himself points to this ambiguity in NE (see A 6.6.171 and A 6.6.210). In the definition, I read him as using “cogitation” in the wide sense. 60 Attentio est cogitatio cum desiderario cognoscendi.


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disposition. In virtue of the memory disposition, the content of the original fleeting perception

is kept present in accessible form. It also requires an actualisation of this disposition as an act

of immediate content-repetition. Finally, cognitive appetites must occur that aim at knowledge

about the represented object.

Pushing the proposed analysis of the attention condition further requires an explication of

the idea of cognitive appetites. In general, appetites are strivings originating from the

primitive active force of monads.61 They are strivings towards some good and they are

efficacious in that they contribute to bringing about new perceptual states. In the case of

appetites constitutive of acts of attending, the good striven for is knowledge and, thus,

cognitive in kind. We can speak of an attention system, which operates on sensory contents

that newly enter memory. This attention system is constituted by and is operative in virtue of

the present cognitive appetites. Depending on the overall situation of the monad in question,

these cognitive appetites can be “interested” in sensed objects in many different ways. For

instance, if the monad is affected by bodily needs, the cognitive appetites “ask” whether there

is any object among the objects sensed that might satisfy the bodily need. Or if the monad is

afraid of being harmed, the cognitive appetites “ask” whether any of the sensed objects are to

be expected to cause harm. Apart from these more specific and temporary cognitive appetites,

there will be more general and permanent ones, which “ask” for whether there is anything

new going on in the current sensation compared to what was sensed before; whether or not

what is new in the current sensation is in line with what was expected; and whether there is

any dangerous object among the newly sensed ones of which harm is to be expected.

How can suchlike cognitive ends be achieved? This question concerns the means available

for achieving the end of receiving knowledge about the represented object. The means

available are, of course, the cognitive capacities of the monad in question. Since the cognitive

capacities of non-rational and of rational animals differ, they need different treatments. Since

I confine myself to animal sensation in this paper, I will only take into consideration cognitive

capacities shared by non-rational and rational animals. What both share is what I call

“associative cognition”, which is essentially memory-based. The central capacity of

associative cognition is associative reasoning, which is, as Leibniz says, “only a shadow of

[rational, CB] reasoning”62. Associative reasoning rests on memory since the conclusions of

associative reasoning are expectations and expectations contain recurring contents, i.e., they

are contents the animal soul has sensed earlier in similar circumstances. In PNG 5, Leibniz

61 See M 15. 62 A 6.6.51.


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famously illustrates associative reasoning with regard to a dog that expects pain when he sees

his master carrying a stick:

There is interconnection among the perceptions of animals which bears some resemblance to reason, but this

interconnection is only founded in the memory of facts or effects, and not at all in the knowledge of causes. That

is why a dog runs away from the stick with which he was beaten, because his memory represents to him the pain

which the stick caused him.63 (GP VI 600 / AG 208)

The dog example already appears in NE, where Leibniz explicitly points out that human

beings also engage in associative reasoning:

Beasts pass from one imagination to another by means of a link which they have there previously sensed. For

instance, when the master picks up a stick the dog fears being beaten. And in many cases children, and for that

matter grown men, move from thought to thought in no other way but that. This could be called ‘inference’ and

‘reasoning’ in a very broad sense. But I prefer to keep the accepted usage, reserving these words for man and

restricting them to the knowledge of some reason for perceptions’ being linked together.64 (A 6.6.143 / RB 143;

translation modified)

Not only beasts but animals in general are capable of a kind of reasoning in a broad sense

of the term, which consists in associative reasoning, though only rational animals are capable

of rational reasoning guided by knowledge of causes and eternal truths. Associative

reasoning, in contrast, consists in habitualised transitions from one sensory content to another.

These transitions occur in virtue of associative links that are established between sensory

contents due to earlier experiences of their interconnectedness. For instance, in the soul of a

dog that has been beaten by its master several times, an associative link is established between

the sensory image of the stick and the feeling of pain caused by being beaten with this stick.

Seeing its master picking up the stick again revives the stored feeling of pain and the dog

expects to feel pain again very soon. So, what associative reasoning results in is the activation

of stored knowledge about sensed objects. The aim of knowing, which the cognitive appetite

targets, turns out to be the aim of activating stored knowledge rather than acquiring new one.

63 Il y a une liaison dans les perceptions des Animaux, qui a quelque ressemblance avec la Raison: mais elle n'est fondée que dans la memoire des faits ou effects, et nullement dans la connoissance des causes. C'est ainsi qu'un chien fuit le bâton dont il a été frappé, parce que la memoire luy represente la douleur que ce bâton luy a causée. 64 Les bêtes passent d’une imagination à une autre par la liaison, qu’elles y ont sentie autres fois. Par exemple quand le maistre prend un baston, le chien apprehende d’étre fraggé. Et en quantité d’occasions les enfans de meme que les autres homes n’ont point d’autre procedure dans leur passages de pensée à pensée. On pourroit appeller cela consequence et raissonnement dans un sens fort étendu. Mais j’aime mieux me conformer à l’usage recû, en consecrant ces mots à l’homme et en les restraignant à la connaissance de quelque raison de la liaison des perceptions[.]


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This activation, in turn, results in expectations concerning events in near future and enables

the animal to prevent harm, but also to take advantage of favourable circumstances.

I said above that cognitive appetites aim at knowledge about a represented object. Which

kind of knowledge these appetites are “asking” for at least partly depends on the overall

situation of the monad in question (being in need of something; fearing harm; searching for a

particular object; etc.). Associative reasoning is an important means for achieving cognitive

aims in animal souls: It activates experience-based knowledge about objects of sensation as in

the case of scrutinising the sensed vicinity for objects that might satisfy one’s bodily needs

(hunger, thirst) or for objects that might be harmful (as in the case of the dog). Other

operations that belong to what I call “associative cognition” include comparing new sensory

contents with foregoing ones in order to detect the appearance of new objects in one’s

vicinity. It also includes operations of comparing memorised representations of objects, which

are searched for, with newly appearing objects. And there are also operations of comparing

expectations concerning what will happen with sensations of what actually happens.65 The

cognitive appetites constitutive of sensation bring cognitive activities like these about in order

to achieve their cognitive end. This means that Leibniz holds a cognitive conception of

sensory attention. Attending to an object represented in sensation comes down to attending to

it cognitively by executing operations of associative cognition as a means to achieve the

cognitive end. Hence, sensory attention is not a matter of an inner sense “observing” a present

representational content. It is not as if the animal is “looking inside” and “focusing on” the

content of a distinguished act of immediate content-repetition. Instead, sensory attention is a

matter of bringing into play (or attempting to do so) cognitive capacities, in particular of

activating experience-based knowledge with regard to the represented object.

Let me finally bring together the components of conscious sensations that have so far only

been discussed separately. In doing so we see that, for Leibniz, sensation and in particular

conscious sensation is a complex affair:

(a) Distinctness Condition: Sensation requires a distinguished perception.

(b) Memory Condition: Sensation requires that a memory disposition be established in virtue

of the distinguished perception.

65 The outcome of the last kind of checking can lead to different cognitively significant behaviour. If the incoming sensation fits the expectation, nothing might happen except for the fact that the associative link between the two events in question gets strengthened. However, if the expectation is frustrated, a state of “surprise” arises that can lead to behaviour such as further observing or even actively exploring what was unexpectedly sensed. If the sensed event is itself associated with danger, it might also cause flight behaviour. Within the confines of this paper, however, I will not go any further into the details of associative cognition.


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(c) Attention Condition: Conscious sensation additionally requires the actualisation of the

memory disposition in form of an act of immediate content-repetition to which cognitive

appetites attach. These appetites set into motion associative cognition (like associative

reasoning) with the aim of achieving memory-based knowledge about the represented object.

5. Sensory Apperception

Before we come to the concluding section of this paper, I would like to shortly address a

fourth characterisation of sensation, which connects sensation to the notion of apperception.

In NE Leibniz states that “sensation [occurs; CB] when one apperceives an external object”66.

The notion of apperception is one of the most controversial notions in Leibniz’ theory of

cognition. According to the prevalent interpretation, Leibniz considers acts of apperception to

be acts of reflection.67 In general, I doubt that this interpretation is correct.68 One notorious

problem this interpretation faces derives from Leibniz’ attribution of apperceptions to non-

rational animals. Since Leibniz denies animals the capacity of reflection, Leibniz’ notion of

apperception should not be tied to the notion reflection. Hence, it is important to note that the

proposed interpretation of Leibniz’ conception of sensation avoids this problem and shows

how apperception can be understood in a non-reflective sense (at least within the context of

sensation). When Leibniz defines sensation as apperception of outer objects in NE, what he

refers to by the notion of apperception is the act of attending to a represented outer object that

is constitutive of sensation.69 And as we have seen, this act of attending does not consist in an

act of reflection but in an act of immediate content-repetition that is involved in cognitive

processing due to a cognitive appetite. In sum, Leibniz holds a first-order attention account of

sensory apperception, where the notion of attention is not explicated in terms of reflection, but

in terms of cognitive appetites and resulting cognitive activity.

6. Conclusion

66 A 6.6.161 / RB 161, translation modified. 67 See R. F. McRae: Perception, Apperception, and Thought, Toronto, 1976 and M. Kulstad: Leibniz on Apperception, Consciousness, and Reflection, München, 1991. 68 See C. Barth: “Apperception in the New Essays Concerning Human Understanding. A Critique of the Reflective Account and a Sketch of an Alternative Proposal”, in: H. Breger/J. Herbst/S. Erdner (Hg.): IX. Internationaler Leibniz-Kongress - Natur und Subjekt. Vorträge 1. Teil, Hannover, 2011, 37-43 and C. Barth: “Leibnizian Conscientia and its Cartesian Roots”, forthcoming in Studia Leibnitiana. 69 Note that there is also a difference between the definition of sensation in terms of apperception and the former three definitions. In the former, Leibniz only refers to the act of attending to an outer object leaving out the original distinct perception. And one might think that this points to a substantial difference between both characterisations of sensation. However, I think that we should not understand his definition of sensation from NE in this way. Instead, when Leibniz defines sensation as apperception of an outer object, the reference to the original distinct perception from which the act of immediate content-repetition draws its content is tacitly referred to as a precondition of the occurrence of the latter act.


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In this paper, I have presented a reconstruction of Leibniz’ conception of sensation as it

applies to non-rational as well as to rational animals. We have seen that, for Leibniz,

sensations are complex acts. Sensations in the general sense require a distinct perception that

establishes a memory disposition. Conscious sensation, in turn, additionally requires that the

disposition is actualised in form of an act of immediate content-repetition, and that cognitive

appetites attaches to this act that aim at knowledge about the represented object. We have also

seen that Leibniz’ account of sensation implies an understanding of sensory apperception and,

thus, of sensory consciousness in terms of cognitive attention. This understanding takes

Leibniz to hold a same-order view of sensory apperception. It does so without relating

apperception to acts of reflection and, thus, avoids the notorious animal problem.

Finally, let me highlight two further sets of problems, which need to be answered in order

to yield a comprehensive account of Leibnizian sensation:

First, we need an account of the images that form the contents of the acts of immediate

content-repetition. Note that, as I would argue, these images are not already contained in the

original distinct perception. The notion of an image needs explanation.70

Second, we also must account for the differences, in Leibniz’ view, between sensation of

non-rational and rational animals. Rational animals possess sensory ideas and sensory

thoughts in addition to sensation with images, whereas non-rational animals merely possess

sensation with images and lack sensory thoughts. Hence, in order to give a full account of

sensation in rational souls, we need to explain the origin of sensory ideas, their role in sensory

thoughts, and the relation between sensation with images and sensory thought.71

70 Martha Bolton has recently presented a suggestion of how this process should be understood (see Bolton, 149-151). 71 I would like to thank Ramona Winter for linguistic corrections. I am responsible for all remaining linguistic mistakes, of course. I am also indebted Martha Bolton for invaluable discussions on the topic of this paper.

leibniz’s conception of sensation (studia leibnitiana sonderheft 46)

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