»

(V)

15

Stt~l*

[Reprinted from The American Behavioral Scientist, May 1965, Vol.

VIII,

No. 9]

Computer Simulation of IndividualBelief Systems*

Robert P. Abelson and J. Douglas Carroll

In this paper we sketch an attempt at computer simu-lation of individual belief systems. Although rooted ina series of earlier formulations (Abelson and Rosenberg[1958], 1 Abelson [1959],- Rosenberg and Abelson [1960],3

Abelson [1963]'), this complex project has not heretoforebeen totally outlined in print. We shall begin with severalclarifying comments on the nature of our goals and theproblems we have faced, thence proceeding further andfurther into the details of operation of our simulation.

By an individual belief system we refer to an interre-lated set of affect-laden cognitions concerning some as-pects of the psychological world of a single individual.In simulating such a system, our intention is not only to

represent its structure of interrelationships, but also someof the processes by which the system maintains itselfagainst the intrusion of new and potentially upsetting in-formation. Our use of the technique of computer simu-lation is intended to maximizethe explicitness with whichwe state our assumptions and the vividness with whichthe consequences of these assumptions are made apparent.The operation of simulated belief systems can be playedout on the computer and the details scrutinized in orderto refine our level of approximation to real systems.

The psychology of belief systems lies athwart the an-cient philosophical battleground of whether man is ba-sically "rational" or "irrational." Without claiming to haveresolved this honorable controversy, we adopt the usefulcompromise position current among social psychologiststhat man is "subjectively rational," i.e., rational within theconstraints of his own experience and motivation. Thisposition owes much to Heider's5' r' analysis of "naive psy-chology," and can be found implicitly or explicitly in thework of many "cognitive consistency" theorists (Festin-ger7

;

Osgood and Tannenbaum"; Rosenberg and Abel-son3 ). To be sure, there is still much room within thiscompromise position for differences in emphasis as be-tween motivational and cognitive components of the totalsystem. The work of Rokeach0 and Smith, Bruner, andWhite'" among others reminds us that individual beliefsystems areheavily determined by personality needs. Our

* The work herein reported was in part supported by GrantMH-0 1682 from the National Institute of Mental Health, I'nitcd StatesPublic Health Service. We wish to thank Mr. William Rcinfeld forcarrying out the comput.r programming for the simulation model.

simulation is nevertheless primarily a cognitive model, notper sc a personality or motivational model, nor (as withmany aspects of FestingerV dissonance theory) an actionmodel. The cognitive processes of our system are drivenhy motivational forces, but are also quite responsive to"reality" fas perceived by the individual). The achieve-ment of a balance of forces between self-interest andreality is one of the most difficult theoretical problemsin the psychology of belief systems. It is far too glibto assumethat "people believe what they want to believe."since unpleasant realities must often be accepted in someform, and pleasant absurdities must often be rejected.The way in which our simulation attempts to tread thisthin line is outlined later.

A second problem area pertains to the degree of mu-tability inherent in belief systems or. more properly, therange of tolerance for change under appropriate circum-stances. Among our assumptionsrelevant to this question,the following three are crucial: 1) The greater the affectassociated with the elements of a belief, the greater theresistance to any change in that belief or am reductionin the strength of that

affect;

2) The more "closed" (i.e..massively self-consistent) a belief system, the greater thelikelihood that resistive mechanisms will succeed; 3) Sub-stantial changes can take place only when resistive mech-anisms are not invoked, or when they fail.

The last assumption, which might be rephrased, beliefchange and affect change arc the default of resistance.is not an empty proposition. The conditions for the useand success or failure of resistive mechanisms are pre-cisely specified in our simulation.

Another thorny dilemma in the design of a simulationsuch as ours is the choice of a linguistic structure inwhich beliefs are to be stored for later processing. Togive the system a full command of natural language isfar beyond the realm of present feasibility, but a limitedcommand of a kind of pidgin English is entirely possible.Our system has a rudimentary grammar which enables itto cope with a rather wide variety of \ erbal material.However, we must pay a price in both system flexibilit\and psvcholinguistic sophistication to bu\ simplification

In an interesting discussion of psycholinguistic prob-lems. MilU;r" discusses three possible levels of analysis;syntactic, semantic, and pragmatic. Syntactics pertains to

24

2.-:MAY, 1965

the distinction between the grammatical and the ungram-matical; semantics, between the meaningful and the mean-ingless; pragmatics, between the- acceptable ami theunacceptable. Our system has syntactic capability interms of certain limited sentence-processing rules. How-ever, it does not have separate semantic and pragmaticcapabilities, since the former is largely subsumed by thesystem under the latter. To illustrate, consider the twosentences, "Lamps eat geology," and "Barry Goldwaterbelieves in socialism." The first is semantic nonsense-,whereas the second is potentially meaningful but obvi-ously false. Our system somewhat distorts this distinction.Given sufficient information to recognize and deal withthe sentence components, it would immediately adjudgethe second sentence incredible, but would spend a greatdeal of time in futile memory search before concludingthat it could not clearly regard the first sentence eitheras credible or incredible. A separate semantic capabilitywould enable the system to identify nonsense immedi-ately, but we have bypassed this design problem to con-centrate directly on pragmatics.

One further remark concludes this introductory section.In the article referred to above, Miller notes, "At thepresent time, linguists and logicians have a rather deepunderstandingof syntax. . . k The general shape a semantic-theory must assume- is slowly emerging. Pragmatics, how-ever, is still the wastebasket into which all miscellaneousand confusing problems are put ..." ln view e>l suchadmonitions and in the light of common sense, it is ap-parent that we are on pioneering ground and regard ourtheory as subject to considerable modification.

We now proceed to outline the details of the system.

The Memory Structure

The standard linguistic unit in which beliefs arc- storedis a sentence, consisting of a concept followed by a predi-cate. A predicate typically consists of a verb followed bya concept. Thus a sentence is in effect a concept-verb-concept (i.e., subject-verb-object) construction referringto a state of affairs which the system "believes." Sincea "state of affairs" can itself be cognized as an elementalunit, every sentence in the system may also function asa concept to which other elements may be affixed to formcompound sentences. For example, consider the initialsentence. "Cuba subverts Latin America" formed fromthe concept "Cuba" and the predicate "subverts LatinAmerica." This sentence can in certain contexts be re-garded as the noun phrase, "Cuba's subversion of LatinAmerica." Thus a belief concerning Kremlin control ofthe presumed subversion could be carried by the sentence,"Russia controls Cuba's subversion of Latin America."In our terms, "Russia" is of course a concept, and "con-trols Cuba's subversion of Latin America" is a predicate.

This kind of packaging of one belief within another isan important feature of our system, for it permits withsimple syntax the orderly storage of important concep-tions about responsibility, causation, and impact involvingthree or more actors and actions. The network of beliefs

so stored may be said to comprise the "horizontal" struc-ture of the- belief system.

For a demonstrational system presently being assem-bled by tlie first author, it appears that between 500 and1,000 sentences are necessary to capture; the basic themesand illustrations expressing the publicly state-el foreignpolicy beliefs of a particular individual (a wc-11-knownright-winger). It should be noted, however, that a sub-stantial portion of this corpus of sentences is devoted todefinitional information rather than to beliefs per se.For example-, consider the sentence. "Colonial powersoppose anti-colonial policies." This statement is very closete) a tautology and hardly enriches the system at all.However, if this sentence were omitted, the- simulatedsystem might not "understand" the meaning of the con-cept "anti-colonial policies." As far as the system isconcerned, the denotative meaning of an element residesentirely in structural connections of that element withother elements. Thus, if the only reference- in the- systemte> "anti-colonial policies" were, say, "The U.N. promotesanti-colonial policies," the system would be unable- to usethis belief meaningfully. It might just as will find storeda nonsense term in this sentence-, such as "The U.N", pro-motes squadgy widge." This digression establishes thatsome of the "beliefs" of the system should technically he-regarded instead as "knowledges."

Another portion of the memory structure is a "vertical"network among the elements. The basic vertical connec-tion between elements is the instance relationship. Theinstances of a concept are those other concepts whichrepresent "kinds of X" or "examples of X." Instances maythemselves have instances, and so on.

Many instance relationships embody simple objective"knowledges," e.g., "Brazil" as an instance of the- concept"Latin American nation." There may also be a subjectivequality involved, as with "India" as an instance- of "left-leaning neutral nations."

Compound concepts, e.g., "The Communists seek a Com-munist-dominated world," may also have exemplifyinginstances, e.g., "The Communists take over free nations.'Predicates " are also subject to the instance relationship;for example, "distributes atheistic propaganda" could be-an instance of "promotes atheism."

The obverse of the relation "V is an instance of X" is"X is a quality of Y." Thus, "Latin American nation" is

a quality of "Brazil," and similarly for the- other examplesabove. Metaphorically we conceive of a hierarchy oflevels of abstraction, in which the instance- relation points"down" from the general to the specific, and the quulihrelation points "up" from the specific to the general. Thesystemic significance of this entire vertical network is thatit encodes the subjective codifications and categories usedby the system. It is the system's particular wav of parsingfrom reality the "who" and the "what" entering the hori-zontal network of who does what, what causes what, andso on.

Several other features have been incorporated into thememory structure. The most important of these- concernsthe affective investment of the system in its beliefs. It

THE AMERICAS HEUAVIOHAL SCIESTIST26

-

is beyond our purview to simulate the inner dynamicsof human affect, but it is imperative that affective influ-ence upon cognition be represented. We have chosenthe simplest big step in this direction by providing forthe storage of evaluations of elements. Every element,whether concept or predicate, carries a signed quantita-tive evaluation summarizing the resultant of all positiveor negative affects attaching te> the element. These evalu-ations exert a heavy guiding influence upon certain cog-nitive operationsof the system, and arc- in turn sometimessubject to change consequent upon certain cognitive out-comes. The details are sketched later.

Cognitive Processes

The present system is provided with two major cog-nitive processes (sub-routines, in computer programmingparlance). These two processes can operate in differentcircumstances upon a variety of contents. One- process

we label the "Credibility Test"; the other, the "Rationali-zation Attempt." Several system capabilities are- providedby these two processes, as will unfold in the course ofour description of their operation.

The CredibilityTest is employed by the system in tworather different ways: to screen incoming sentences forplausibility and to check -the reasonableness of self-pro-duced sentences which the system would "like to believe."The input to the process is a sentence (i.e., a concept-predicate pairing), and the output is one of three alter-native judgments: that the sentence is credible, that itis dubious, or that it is incredible.

The obvious first response of the system in testing thecredibility of an input sentence is to consult its memoryto see if the sentence (or its opposite) is already stored.If this simple operation fails, then the Credibility Testrelies upon other information in the vertical memorystructure. The details of the process are quite elaborate,and only the main ideas will be sketched here.

Denote the input sentence symbolically as C-P. Forthe sake of a concrete illustration, suppose that the con-cept C is "Liberals," and the predicate P is "support anti-colonial policies." Suppose further that the system doesnot have in its memory either the input sentence, "Lib-erals support anti-colonial policies" or the contrasting sen-tence, "Liberals oppose anti-colonial policies."

What happens next is that a systematic search of be-liefs about the instances of C will be undertaken. Fen-each instance C; (e.g., "Stevenson"), the system exam-ines all beliefs CrPj (e.g., "Stevenson makes floweryspeeches," "Stevenson ran for President," etc. ) to seewhether a Pj can be found which is an instance of theoriginal P. For example, the critical predicate here mightbe, "opposes Portugal on Angola," an instance of "sup-port anti-colonial policies."

In effect, a chain of inductive evidence supporting C-Pmay be found by going "down" to Ci, "across" to Pj; andback "up" to P. Thus "Stevenson opposes Portugal onAngola" lends some credence to the generalization, "Lib-erals support anti-colonial policies." However, the lo-

cation of a single such chain is not necessarily sufficientto support the generalization. It depends upon the rela-tive number of instances of C through which such chainsexist. Another instance of "Liberals" in our example mightbe "Earl Warren," and the system might find no exampleof any kind of anti-colonial policy supported by Mr. War-ren. Thus the system must have some criterion by whichit balances off successful and unsuccessful searches.

We have given the system the following rule: Thesentence C-P is considered credible if at least half of theinstances of C arc found to be connected in a belief sen-tence- with at least one- instance P. This "majority" rulemay smack of a certain arbitrariness, but it seems at leastas reasonable as any other rule we might have postulated.(In a later section we report an empirical study withimportant implications for the choice of a rule.)

If the system fails to establish the inductive credibilityof a sentence C-P, it is given the option under some cir-cumstances of testing the inductive credibility of theopposed sentence, C-not P ("not P" is the- predicate-formed from P by negating the verb). Should this testsucceed, the original sentence C-P is adjudged not credi-ble. Should this test fail (or not be invoked), the- Credi-bility Test process proceeds to undertake a somewhatmore complicated search involving the qualities ratherthan the instances of C and P.

Search proceeds up the vertical tree and thence backdown to the level of C-P. The effort is made to establishthe credibility of C-P deductively by first establishing thecredibility of several higher-level generalities. The rulefor this sub-process is that at least half of the qualitiesof C must be found credibly related to at least one qualityof P. In this latter search, the previous inductive m cha-nism may again be invoked.

Perhaps the further pursuit of our previous examplewill clarify these circumlocutions. One of the qualiti -s of"Liberals" might be "Left-wingers" and one quality of"support anti-colonial policies" could be (in the subjectivete-rms of a right-wing view) "mistreat U.S. fricucls abroad.'

The credibility of "Left-wingers mistreat U.S. friendsabroad" (if not previously established by the system)could be examined in terms of the- instances of its com-ponents. The system would search to see whether atleast half of the instances of "Left-winger" were connectedto at least one instance of "mistreat U.S. friends abroad."One instance of "Left-wingers," say, "Administration the-orists," might be found connected with "coddle hit-leaningneutral nations," an instance of "mistreat U.S. friendsabroad." A sufficient number of further instances of "Left-wingers" might similarly be connected with instances of"mistreat U.S. friends abroad." establishing the credibilityof this sentence. A similar process applied to other higher-level sentences might then eventually satisfy the rule forestablishing the deductive credibility of the original sen-tence C-P, "Liberals support anti-colonial policies."

If the rule is not satisfied, then this entire search processmay under some circumstance's be repeated on the op-posed sentence, C-not P. If this is done, but fails, thenthe Credibility Test process will terminate- with a signal

27MAY, 1965

that it can find insufficient evidence- erne- way or the otherabout C-P. As far as the system is concerned, the sen-

tence is neither credible nor incredible.The above- description covers the essentials of opera-

tion of the Credibility Test. There are some additionalwrinkles, such as mechanisms for discovering new in-stances and qualities by parsing compound elements, forsearching two or three levels clown or up in the verticalstructure, and for terminating very long searches becauseof "fatigue." but the details will not be given. It is note-worthy that the two major sub-processes alone are capableof generating a very large quantity of subjective evidencerelevant to the credibility of an assertion.

Although our description of the Credibility Test maymake it appear to be a more or less neutral process in-nocent of the affective investments of the system, thisis not necessarily the case-. One fundamental use of tin-test is in the mechanism we label Denial. In this mecha-nism, the- system takes a sentence C-P which is crediblebut upsetting, constructs C-not P. and enters the Credi-bility Test with the injunction to find C-not P credibleif at all possible. Success in this procedure enables thesystem to deny C-P by means of contrary evidence.

The other fundamental process of the system, "AttemptRationalization," is applied only to sentences which thesystem is motivated to "explain away." Such sentencesare characterized by evaluative inconsistency or imbal-ance between concept and predicate, for example, a posi-tively valued actor (concept) connected to a negativelyvalued action (predicate). The function of the rationali-zation process in these cases is to deny the psychologicalresponsibility of the actor for the action. This can bedone in three primary ways: 1) by assigning prime re-sponsibility for the action to another actor who controlsthe original actor; 2) by assuming that the original actionwas an unintended consequence of some other actiontruly intended by the actor; 3) by assuming that theoriginal action will set other events in motion ultimatelyleading to a more appropriate outcome.

These three mechanisms represent sub-processes of"Attempt Rationalization," respectively labeled "Find thePrime Mover," "Accidental By-product," and "ReinterpretFinal Goal." Each of the three depends upon the dis-covery by the system of a critical element specially re-lated to either C or P in the original sentence C-P. Thiscritical element must be- either: a concept. B, occurringin a belief sentence of the form. "B controls C"; or apredicate, Q, occurring in a phrase, "Q can accidentallycause P"; or a concept, R, occurring in "P may lead toR." The existence of such elements in the system isdependent upon some special memory storage provisionswhich we have not heretofore mentioned, especially forphrases linking two predicates. These provisions have-been made, but we shall ne>t discuss the necessary syn-tactical maneuvers here. We- shall limit ourselves to anexplication of what is involved in the sub-process, "Findthe Prime Mover." (Some- discussion ol the other twosub-processes may be found in an earlier paper by Abel-son').

The system takes the- sentence C-P, constructs the predi-cate "controls C" and searches its memory for a beliefof the- form, "B controls C," where B is a concept moreevaluatively consistent with P than was C. If none isfound, then the sub-process has failed. If an appropriateB is found, the system then attempts to establish thecredibility of the sentence B-P. If this attempt fails,there is a search for an alternative B. If this attemptsucceeds, however, the-n a successful rationalization hasbeen constructed which might be paraphrased. "The actor(.' was not really responsible for action P. but was merelythe helpless pawn of the wishes of B." To give a moreconcrete example with foreign policy content, supposethat a system with a weak positive evaluation of Cam-bodia is presented with the sentence "Camlx>dia rejectsU.S. advice-." Suppose that this information is foundcredible (for example, in terms of higher-level subjectivegeneralizations concerning the obstreperous behavior ofAsian nations), and that the system subsequently ' at-tempts to rationalize the sentence. A successful outcomemight well be the compound sentence. "Red China con-trols Cambodia's rejection of U.S. advice.

System Control of the Response Proces-es

The response processes outlined above are called uponby the system in an orderly sequence dependent uponthe circumstances. This "calling sequence" constitutes akind of executive function by which the system governsits operations. In the present system, the "executive" isprepared to respond only to assertions fed into the sys-tem in a standard sentence format. After each assertionhas been dealt with, the system waits for another asser-tion. Because it does not operate autonomously in be-tween externally triggered episodes, the present systemis a "one-shot" rather than continuously functioning cog-

nitive system. (In future versions, provision will be madefor continuous functioning. The system will have a"Worries List" on which it stores various bothersomeby-products of previous operations. When there is noinput, the system will consult its Worries List to findsomething to think about, somewhat as Colby and Gil-bert's'- simulation of neurotic thinking runs iterative!)through whole complexes of beliefs.) .

The standard format for input sentences to the systemis "S says C-P," where S denotes the source of the as-

sertion. Specification of ihe source is crucial !<>r theachievement of a realistic simulation. In order to be- ca-pable of evaluating what is said, the system must knowwho says it. Incoming assertions are potentially persua-sive communications, and it is well known that the- effectsproduced by persuasive- communications are critically

dependent upon the characteristics of the communicator(cf. Hovland. Janis, and Kellev ,: ).

In order to use information about communicationsources, the system must have prior knowledge i,or be-liefs) about what sorts of things have- been said by whom.Fortunately, the syntax of our system readth permitssuch memory storage. Any known

Diirce,

S. is simply

THE AMERICAN IiEHAVIOHAL SCIENTIST

28

a concept in the system, and the construction, "says C-Pis a (compound) predicate. Thus constructions ol theform "S says C-P" are (compound) sentences, pote-n---tiallv manipulate by the system in precisely the same

ways

as all other sentences. For example, "S says C-P'can be subjected to a Credibility Te-st and found crediblebecause other persons sharing some ol S's qualities arc

believed to have said things sharing some of the qualitiesof the unit (C-P). Or again, "S says C-P" can be enteredinto the Attempt Rationalization process and a rationali-zation found to the effect that S's statement is in theservice of some ulterior purpose, or is understandable-only as the view of some hidden figure controlling S.and so on.

The system "executive" decides which processes are to

be applied in what order to "S says C-P" as well as whichprocesses are to be applied to the inner sentence "C-P"itself. Of course the executive is not a homunculus;choices of processes are actually automatically made as

a function of the system's prior evaluations of three ele-ments of the input': the source-

S,

the- predicate P, andthe compound concept (C-P). We- cannot in this briefexposition give the flow chart for the entire executiveprogram, but we can indicate the major branches.

The first thing the executive does is to test the credi-bility of the input components. Test failure gives rise-to an "incredulity reaction," and processing stops. Testsuccess, however, does not imply system acceptance ofthe input. The executive next examines its evaluation ofS. If the source is negative, then the system is motivatedto dismiss the source's assertion either by denial or ra-tionalization, especially if the concept and predicate ofthe assertion are evaluatively inconsistent. If the; sourceis positive, neutral or unfamiliar, then the executive next

inspects the evaluative consistency of C and P.The case of consistent evaluation sends the system

quickly into a terminal branch. There is not much leftfor the system to do when a favorable source makes acredible statement that a good actor is engaged in a goodaction or a bad actor is engaged in a bad action, exceptto express joy or regret. (An improved version of thesystem might in the latter case attempt to construct arecommendation for dealing with the bad actor.)

The case of inconsistent evaluation is more complicated,and the two major sub-cases must be treated somewhatdifferently from each other. If a good actor is assertedto be engaged in a bad action, then the system is mo-

tivated primarily to deny this alleged fact or to denythat the assertion was made. If a bad actor is assertedto be engaged in a good action, the system is motivatedprimarily to rationalize this alleged fact or to find a

reason why the assertion was made. At any rate, theexecutive lias at its disposal all four of the- above mecha-nisms, namely: Deny (C-P); Deny (S says C-P); Ra-tionalize (C-P); Rationalize (S says C-P).

In one way or another (possibly including the failureof all processes attempted), system control finally, passesfrom the executive, and a response is printed out. Al-together there are 32 possible- types of responses in the

present version ol the system. These responses needmerely be indexed symbolically so that the- person run-ning the simulation can find out what the- system did.For entertainment value, however, the system has beenprogrammed so that a prepared English statement de-notes each response. Thus, particular e-xits from the- sys-tem

may

be accompanied by luiiel remarks such as,"That's just the kind of nonsense- I'd expect to hear fromhim," or "That news shakes me- op. Did he say anythingelse about

it?,"

and so on.When the denial or rationalization processes succeed,

the- supporting evidence or reasoning developed by thesystem is printed out. In order to do this, the- systemdecodes its internal symbols into English by means ofan internal "dictionary" provided to it. and then insertsthese English words into appropriately pre-packagedlinguistic frames such as "(C) only (?) in order to achieve

Thus the entire printed output of the- syste-m for eachone-shot lesponse is in more or less coherent English.We hope soon to be able to express the input in (sim-plified) English as well, so that a smooth "interview"with the system may be conducted. (At present, the in-put is symbolically coded. The programming language.IPL-V, in which the syste-m is presently programmedrenders the use of verbal input very clumsy.)

Effects of the Processes on the System

We have given many details of how the system pro-duces responses of a resistive character, but have as yetsaid nothing about the- changes which take- place in thesystem itself. In the course of its machinations, the svs-tcm undergoes four types of changes: 1 ) the creation ofnew instances to include in its vertical

memory

structure;

2) the- gradual development of a "style" of rationalizationfor particular contents; 3) the storage- of new beliefsfound credible- and not later denied or rationalized; 4)

gradual evaluative changes.The creation of new instances is an incidental by-

product of the- Credibility Test. In searching for an in-stance of a compound concept (C-P). the syste-m may.

for example, discover that an instance C, of C forms anadmissible compound concept (C.-P) when paired withP. If (Cj-P) had not previously been stored ..s an in-stance of (C-P), it is so stored. Much more complicated(and thus more interesting) examples are within therange of system capability, but in a sense- none of thesenewly created instances are very "creative," since theyarc- all strongly implied in the original memory structure.

Development of a "rationalization style" is made pos-sible by provision for the system to remember the wayin which it has rationalized any particular sentence.

When the- need arises to rationalize a new sentence, thesystem first finds a sentence similar to the new one- ( bymoving up and down the vertical network to "nearbyconcepts and predicates), and then looks to see whatrationalization sub process and crucial element (B. Q,or R)

may

have been used on that similar sentence. If

29

MAY, 1965

such information can be found, a similar rationalizationattempt is applied to the new sentence. Thus over thelong run the use of a particular rationalization mode maysnowball and give the system a certain stylistic character,whether it be paranoid (through excessive use of "Findthe Prime Mover"), or apologetic ("Accidental By-product"), or Polyannic ("Reinterpret Final Goal"), ora blend of these.

The storage of new beliefs can come about at severalpoints in the system. If an input unit C-P (or S says C-P)is found credible and not later denied or rationalized, itis stored when the system makes its output response.Moreover, the Credibility Test may discover and certifyadditional higher-level beliefs during the- course of itsexamination of the qualities of C and P, and these tooare stored when appropriate termination points arc-reached. Yet a third possibility is that certain new sen-tences will be generated by the application of the Credi-bility Test during a rationalization attempt. Success ofthe rationalization process automatically leads to storageof such new sentences. One restrictive feature embeddedin the Credibility Test is worth emphasizing, however.Even though it is cpiite possible for both a sentenceand its opposite to be found credible, in no case can a

sentence C-P be found credible if the sentence C-not Pis already stored in the system. Flat contradiction of priorbeliefs, then, is not admissible in the present system. Itis quite possible, however, for innocent-seeming beliefsto slip past the Iron Duke of resistance and later causemajor shifts in emphasis of the belief system. The designof future versions of the system will take into accountvarious other ways in which belief systems can ultimatelybe drastically modified (for example, by firm attachmentof beliefs to particular sources who later become- dis-credited, thus converting a belief into a "disbelief").

Evaluative changes are incorporated into the systemin a rather novel way. We have postulated that changesin the evaluations of elements can occur only when thesystem is "thinking" about these elements. When twoelements are simultaneously present "in thought," wepostulate that "evaluative transfer" takes place betweenthem. The system definition of what it means for a pairof elements to be simultaneously "in thought" is that aparticular concept and a particular predicate are bothunder the direct control of the executive at a particularpoint in time. One clear occurrence of this condition isat the moment when a sentence C-P is input to theCredibility Test. At this moment (and at other com-parable moments) a very small fraction of the evaluationof C is transferred (i.e., algebraically added) to theevaluation of P, and a very small fraction of the evalua-tion of P is transferred (algebraically added) to theevaluation of C. The effect of this transfer is that if Cand P have the same evaluative sign, both evaluationswill be boosted to greater quantitative extremity, but itC and P have opposite evaluative signs, both evaluationswill tend to "run down" toward neutrality. It is preciselythe latter effect which we take to be basically disturbingto the system, thus motivating the use of the denial and

rationalization processes. Hut if these resistive- attemptsconsume a great deal of cognitive effort and ultimately

fail,

the- system will be repeatedly and inescapably ex-posed to small dose-s of evaluative transfer which mayaggregatively result in substantia] evaluative- change, in-cluding changes of evaluative sign. This will especiallybe the case when one or the- othe-r element has a we-akinitial evaluation. A very "tight" or "closed" belief systemwill tend not to be- subject to this effect because it will"have an answer for everything, ' but a more- "open" sys-tem with many internally unresolved questions and quali-fied beliefs will be more vulnerable to appropriate- pe-r--suasion, as indeed one would expect.

These common sense outcomes are- inherent in the de-sign of the system, but we have not had sufficient ex-perience in simulating real belief systems to know whetherthe long-run behavior of our computer model will be-fully realistic in mejst major respects.

-Putting a Memory Structure into the System

Readers who have dutifully followed our presentationin ;J1 its sundry details

may

have long since- wonderedhow the system gets its memory structure in the fir^tpace. The basic- answer to this question is that the siilation user must put it in himself, albeit there- arc atleast three

ways

in which this can be dons-.One method is to invent a structure ad lib. li this

(or any other) method is to be psychologically interest-ing, one must have real subjects whose responses canbe compared with the responses of the simulated system.One might possibly have real subjects It am the inventedstructure. The content would have to be fairly limitedin scope and lacking in prior relevance- to the- subjects—a dramatic encounter on Planet X9between weird goodand bad creatures, for example. This method is not with-out its problems, but serious considerate n is be ing _i:\t ■:,

to the possibility of employing it for purposes of testingthe model.

A second method is to interview a re-al subnet to elicit

defining the topic under consideration anil systematicallydevelops the network of further concepts .md predieby means of eliciting frames such as "What are s meexamples of (concept)?" "What actions do

\ou

associatewith (concept)?" <'tc. This procedure is quite similar inspirit to those of modern ethnographers such ..s I rake-,who explore the beliefs he-Id collectively by numbers ola given culture. We have not used this proced ire in fullelaboration, but several interesting opportunities to doso are being considered.

The third course is the one- present!) being undertakenby the first author, A person is chosen whose- beliefsare well understood by the investigator, and these beliefsare paraphrased in order fo "fit them into the memorystructure. The identity of one individual so chosen haspreviously been indicated. His belief svste-m is notably

his own belief structure. This procedure is

\er\

: iboriousbut feasible provided the subject is articulate and co-operative. The interviewer starts with a gei eral

30 THE AMERICAN BEHAVIORAL SCIENTIST

"closed," and the simulation of this system will providea good intuitive; test of certain features of the model.The results will be reported elsewhere. The simulationof the belief systems of other individuals with very dif-ferent views is also being contemplated, but this stepcannot be undertaken lightly, since the; paraphrasing pro-cedure is extremely difficult. One: might suppose thatfully automatic content analysis methods could be appliedto the writings and speeches of public figures, but thereis an annoying technical problem which renders thispossibility a vain hope, even presuming that other ex-treme technical difficulties could be resolved. This an-noying problem pertains to the implicit "knowledges"necessary to define the full belief structure. The proseof public figures ordinarily omits many obvious facts anddefinitions presumably taken for granted both by himand by his audience.

The three procedures outlined above all concern em-pirical tests of the full simulation model. More limitedpartial tc\sting is also possible—indeed, much more feasible.

A Preliminary Empirical Study

One portion of the system eminently amenable to ex-perimental study is the Credibility Test. Since the opera-tion of the test is independent of system evaluations ofthe elements involved, one can employ innocent or non-sense content in setting up an empirical analogue of thetest situation. This was in fact done in a study by Gilsonand Abelson. 15

The study was designed to test a somewhat puzzlingimplication of the success rule for the sub-process wherethe system searches for instances of C and P. That rule,it will be remembered, is that C-P is found credible whenat least half of the instances of C arc connected to atleast one instance of P. There is an asymmetry in thisrule, the full consequences of which were not apparentwhen the rule was initially invented.

The point may be appreciated by consideration of thefollowing two simple cases:

1) There are altogether three instances of a concept,only one of which is connected to a given predicate:

2) There are altogether three instances of a predicate,only one of which is connected to a given concept.These two cases are entirely equivalent except for theinterchange of roles of concept and predicate. Ye:t thesuccess rule is only satisfied for the second case, not forthe first. The asymmetry boils down to the condition thatthe system is willing to take one- predicate instance outof several as roughly representative of the whole predi-cate class, but is not willing to take one concept out ofseveral as roughly representative of the whole conceptclass. That is, the system is more willing to generalizeover a set of related predicates than over a set of relatedconcepts.

In the Gilso'n and Abelson study, subjects were vari-ously presented with "evidence" expressed in the twosimple forms above, and queried whether they wouldagree or disagree with the cmresponding inductive gen

eralizations. Examples of questions using the- two re-spective forms are as follows:

1. Altogether there are three kinds f>f tribes—Southern,Northern, Central.Southern tribes do not have sports magazine-s.Northern tribes have sports magazines.Central tribes do not have sports magazines.Do tribes have sports magazines?

2. Altogether there are three kinds of magazines-sports, news, fashion.Southern tribes do not have sports magazines.Southern tribes do not have news magazine-s.Southern tribes have fashion magazines.Do Southe-rn tribes have magazines?

A variety of subjects, objects, and verbs were used toexplore the effects of specific sentence components onthe tendency to accept generalizations of these forms.

Although the difference was not of substantial magni-tude, there was very clearly a greater tendency to agreewith questions of the second form than the first

form,

fn other words, the subjects were more willing to gen-eralize over predicates than over concepts, as predicted.Another finding of the study was the rather wide varia-tion in agreement frequency as a function of the sentenceverb. The verb "have," for example, was much moreconducive to the acceptance of generalizations than theverb "like."

Our simulation model does not presently take effectsof this latter kind into account, but as the accumulationof experimental results improves our understanding c r thecomplexities of subjective logic and resistive median. =much improved versions will be possible. Obviously v,

,*

have barely begun to scratch the surface in conductingrelevant empirical studies, but it is hoped that by con-verging on the study of belief systems from many anglesat once, substantial progress in this fascinating area willbe made in the next few

years.

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