Lecture 8Lecture 8

1.1. More mental gymnasticsMore mental gymnastics2.2. Tales from the history of scienceTales from the history of science3.3. Popper’s “solution” to the problem of Popper’s “solution” to the problem of

inductioninduction4.4. Which of two possible conclusions about Which of two possible conclusions about

scientific reasoning is Popper actually arguing scientific reasoning is Popper actually arguing for?for?

5.5. Is either argument successful?Is either argument successful?

On a distant island, there are 3 kinds of humans: Knights, On a distant island, there are 3 kinds of humans: Knights, Knaves, and Normals. Knaves, and Normals.

Knights always tell the truth. Knaves always lie. Normals Knights always tell the truth. Knaves always lie. Normals sometimes lie and sometimes tell the truth.sometimes lie and sometimes tell the truth.

Detectives investigating a crime questioned 3 inhabitants, Detectives investigating a crime questioned 3 inhabitants, A, B, and C of the island. They knew one of them had A, B, and C of the island. They knew one of them had committed the crime, but not which one.committed the crime, but not which one.

They also knew that the criminal was a Knight, and that They also knew that the criminal was a Knight, and that the other two they questioned were not.the other two they questioned were not.

The investigators made a transcript of the statements The investigators made a transcript of the statements made by each of the 3 inhabitants.made by each of the 3 inhabitants.

Using logic, did they identify A, B, or C as the guilty Using logic, did they identify A, B, or C as the guilty person?person?

On a distant island, there are 3 kinds of humans: On a distant island, there are 3 kinds of humans: Knights, Knaves, and Normals. Knights, Knaves, and Normals.

A: I am innocentA: I am innocentB: That is true.B: That is true.C: B is not a normal.C: B is not a normal.Which one is the Knight and, therefore, the Which one is the Knight and, therefore, the

criminal?criminal?Identify the possible solutions.Identify the possible solutions.Identify the fact list.Identify the fact list.Evaluate the possible solutions given the fact list Evaluate the possible solutions given the fact list

(which includes what each said) and solve the (which includes what each said) and solve the puzzlepuzzle

A: I am innocent.A: I am innocent.If A is the Knight, …If A is the Knight, …

B: That is true.B: That is true.If B is lying, …If B is lying, …

C: B is not normal.C: B is not normal.If C is lying, …If C is lying, …

Popper: FalsificationismPopper: Falsificationism From “falsifiability” as the criterion that distinguishes From “falsifiability” as the criterion that distinguishes

science from “pseudo-science” to “falsificationism” as science from “pseudo-science” to “falsificationism” as a model of scientific method/reasoning.a model of scientific method/reasoning.

A rejection of all forms of inductivism (both “narrow” A rejection of all forms of inductivism (both “narrow” and Hempel’s “sophisticated” version).and Hempel’s “sophisticated” version). There is no “principle of induction” that will justify induction There is no “principle of induction” that will justify induction

or an inductivist account of scientific method/reasoningor an inductivist account of scientific method/reasoning Like Hempel, Popper emphasizes that there is no Like Hempel, Popper emphasizes that there is no

logic of discovery, but only a logic of justification logic of discovery, but only a logic of justification (testing)(testing)

But, unlike Hempel, Popper argues that the logic But, unlike Hempel, Popper argues that the logic involved in the context of justification or testing is involved in the context of justification or testing is deductivedeductive and specifically the logic of falsification. and specifically the logic of falsification.

Part 2Part 2

Tales from the history of scienceTales from the history of science

Cases of planetary misbehaviorCases of planetary misbehavior

A physicist of the Newtonian era took Newton’s A physicist of the Newtonian era took Newton’s law of gravitation, law of gravitation, NN, the accepted initial , the accepted initial conditions, conditions, CC, and calculated the predicted , and calculated the predicted path of the planet, Uranus. But the planet path of the planet, Uranus. But the planet deviated from the calculated path.deviated from the calculated path.

Did our Newtonian physicist consider, that once Did our Newtonian physicist consider, that once established, the deviation of Uranus from its established, the deviation of Uranus from its predicated path refutes the law, predicated path refutes the law, NN? ?

Well, yes, a few did.Well, yes, a few did.But more proposed that there was another, yet But more proposed that there was another, yet

undiscovered planet whose gravitational pull undiscovered planet whose gravitational pull explained the deviation in Uranus’ predicted path. explained the deviation in Uranus’ predicted path. Using Newtonian theory, they predicted where the Using Newtonian theory, they predicted where the planet would be, its mass, etc.planet would be, its mass, etc.

Was this prediction Was this prediction Ad hocAd hoc? How might we be able to ? How might we be able to decide if it was?decide if it was?

In this case, when they trained telescopes to the In this case, when they trained telescopes to the predicted region of the sky, they discovered the predicted region of the sky, they discovered the planet Neptune and claimed a victory for Newtonian planet Neptune and claimed a victory for Newtonian theory!theory!

Because Neptune’s predicted path Because Neptune’s predicted path alsoalso deviated from deviated from what was predicted, they proposed another planet… what was predicted, they proposed another planet… and discovered Pluto!and discovered Pluto!

Cases of planetary misbehaviorCases of planetary misbehavior

Uh, oh! What to do about the peacock’s tail?Uh, oh! What to do about the peacock’s tail?

As Darwin understood things, Natural As Darwin understood things, Natural Selection cannot “select” a trait that is Selection cannot “select” a trait that is disadvantageous to its bearer – that disadvantageous to its bearer – that compromises its survivalcompromises its survival

So what to do with all the “ornaments” that So what to do with all the “ornaments” that (predominantly) male members of various (predominantly) male members of various species are endowed?species are endowed? The Peacock’s tailThe Peacock’s tail AntlersAntlers Bright colors…Bright colors…

Uh, oh! What to do about the peacock’s tail?Uh, oh! What to do about the peacock’s tail?

It seemed that many such traits were not It seemed that many such traits were not “benign” but actually put those so endowed at “benign” but actually put those so endowed at a distinct disadvantagea distinct disadvantage It’s very hard for a peacock to take off, fly easily, It’s very hard for a peacock to take off, fly easily,

and landand land Young males with antlers often crash into trees, Young males with antlers often crash into trees,

each other, buildings, and so fortheach other, buildings, and so forth Bright colors seem to make an organism an easier Bright colors seem to make an organism an easier

target for preytarget for prey Apparent counter-examples to or falsifiers of Apparent counter-examples to or falsifiers of

evolution by Natural Selection!evolution by Natural Selection!

Uh, oh! What to do about the peacock’s tail?Uh, oh! What to do about the peacock’s tail?

Uh, oh! What to do about the peacock’s tail?Uh, oh! What to do about the peacock’s tail?

Popper’s Falsificationism One problem facing the Aristotelian and One problem facing the Aristotelian and

Ptolemaic model of astronomy Ptolemaic model of astronomy (geocentrism) was its complicatedness (or (geocentrism) was its complicatedness (or what today’s physicists might describe as what today’s physicists might describe as its ‘inelegance’).its ‘inelegance’).

Because it assumed that planets move in a Because it assumed that planets move in a uniform, circular motion and at a uniform uniform, circular motion and at a uniform speed, it had to contend with (among other speed, it had to contend with (among other observations) the apparent “retrograde observations) the apparent “retrograde motion” of some planets. Mars, for motion” of some planets. Mars, for example, seems at times of the year to example, seems at times of the year to stop and go in reverse for awhile before stop and go in reverse for awhile before resuming its regular circular motion… resuming its regular circular motion…

Popper’s Falsificationism But, although this was seen as a major flaw with But, although this was seen as a major flaw with

the geocentric model, the Copernican model, the geocentric model, the Copernican model, alsoalso had to include epicycles to make it compatible had to include epicycles to make it compatible with apparent retrograde motion of planets – with apparent retrograde motion of planets – albeit, somewhat less.albeit, somewhat less.

It was not until Kepler recognized that the planets’ It was not until Kepler recognized that the planets’ orbits are elliptical that astronomers no longer orbits are elliptical that astronomers no longer needed epicycles.needed epicycles.

Popper’s Falsificationism To address the problem, astronomers To address the problem, astronomers

added “epicycles” to planetary orbits:added “epicycles” to planetary orbits: Smaller (but still circular!) orbits compatible Smaller (but still circular!) orbits compatible

with apparent retrograde motion…with apparent retrograde motion… As the story goes, the Copernican As the story goes, the Copernican

hypothesis was much simpler and superior.hypothesis was much simpler and superior.

Popper’s Falsificationism The moral: if the need for epicycles was The moral: if the need for epicycles was

taken to be a reason to reject the taken to be a reason to reject the geocentric model, it was not solved geocentric model, it was not solved (initially) by the Copernican model – but (initially) by the Copernican model – but scientists accepted the latter anyway.scientists accepted the latter anyway.

Part 3Part 3

Popper’s “solution” toPopper’s “solution” toThe problem of inductionThe problem of induction

Popper’s explication and defense of Popper’s explication and defense of falsificationismfalsificationism

1.1. Reiterate (in contemporary terms) why inductive Reiterate (in contemporary terms) why inductive reasoning cannot be justified.reasoning cannot be justified.

1.1. To justify it would require “a principle of induction”, To justify it would require “a principle of induction”, itself known itself known a prioria priori or being the conclusion of a sound or being the conclusion of a sound argument. We do not and cannot have either.argument. We do not and cannot have either.

2.2. Even a probabilistic understanding of inductive Even a probabilistic understanding of inductive reasoning would require its own “principle of reasoning would require its own “principle of induction”, and suffers from the same problems.induction”, and suffers from the same problems.

3.3. So if (as Hume claimed) it might turn out that So if (as Hume claimed) it might turn out that psychologists report scientists (and the rest of us) use psychologists report scientists (and the rest of us) use induction, this is not itself an epistemological issue. induction, this is not itself an epistemological issue.

Popper’s explication and defense of Popper’s explication and defense of falsificationismfalsificationism

2.2. Reject “psychologism”Reject “psychologism” The question of how an idea (hypothesis) occurs to a The question of how an idea (hypothesis) occurs to a

person may be of interest to psychologists, but not to person may be of interest to psychologists, but not to those interested in the logical analysis of scientific those interested in the logical analysis of scientific reasoning (i.e., in the epistemology of science).reasoning (i.e., in the epistemology of science).

The former is concerned with description ; the latter The former is concerned with description ; the latter concerned with questions of justification or validity – concerned with questions of justification or validity – i.e., is normative rather than descriptivei.e., is normative rather than descriptive

3.3. Reiterate the discovery/justification distinction: Reiterate the discovery/justification distinction: HoweverHowever a a scientist arrives at a hypothesis, all that philosophy of scientist arrives at a hypothesis, all that philosophy of science (epistemology) is concerned with is whether the science (epistemology) is concerned with is whether the hypothesis is hypothesis is justifiedjustified..

4.4. Provide an alternative to inductivist accounts of Provide an alternative to inductivist accounts of scientific reasoning and, in particular, a deductivist scientific reasoning and, in particular, a deductivist account of the testing of hypotheses.account of the testing of hypotheses.

1.1. Make use of the fact that while the logic of Make use of the fact that while the logic of confirmation involves a deductively invalid confirmation involves a deductively invalid argument form, and is beset by the (old?) argument form, and is beset by the (old?) problem of induction, the logic of falsification problem of induction, the logic of falsification involves a deductively valid argument form and involves a deductively valid argument form and avoids the problem of induction altogether.avoids the problem of induction altogether.

If H, then IIf H, then INot INot I----------------------------Not HNot H

Popper’s Falsificationism

The tests any proposed hypothesis is (The tests any proposed hypothesis is (or should or should be?be?)) subjected to:subjected to: Internal consistency: does it include any logical Internal consistency: does it include any logical

contradictions/inconsistencies?contradictions/inconsistencies? Is it actually scientific, i.e., falsifiable?Is it actually scientific, i.e., falsifiable? External consistency: is it consistent with relevant External consistency: is it consistent with relevant

theories that are currently accepted?theories that are currently accepted? How does it fare when it is How does it fare when it is testedtested??

So long as a theory avoids being falsified, we say it So long as a theory avoids being falsified, we say it is is corroborated corroborated (weaker than ‘confirmed’).(weaker than ‘confirmed’).

There is no inductive reasoning involved here!There is no inductive reasoning involved here!

Popper’s Falsificationism

Stages in scientific reasoning (as it Stages in scientific reasoning (as it isis or as it or as it should beshould be?)?)

1.1. Bold conjectures [they go out on a limb, Bold conjectures [they go out on a limb, prohibit the occurrence of some set of prohibit the occurrence of some set of phenomena (events, objects, and so forth)].phenomena (events, objects, and so forth)].

2.2. Rigorous efforts to Rigorous efforts to falsifyfalsify the hypothesis by the hypothesis by subjecting it to tests.subjecting it to tests.

3.3. Falsification (or corroboration). If the first, Falsification (or corroboration). If the first, rejection of the hypotheses and search for rejection of the hypotheses and search for andand

4.4. The emergence of a new bold conjecture… The emergence of a new bold conjecture… proceed to steps 2, 3 and 4…proceed to steps 2, 3 and 4…

Popper’s FalsificationismQuestions:Questions:If we reject psychologism (the study of how If we reject psychologism (the study of how

scientists scientists actuallyactually think and reason), is think and reason), is Falsificationism itself an empirical Falsificationism itself an empirical account of account of how they dohow they do or an account of or an account of how, ideally, how, ideally, they should reasonthey should reason??

If the former, is it in fact If the former, is it in fact howhow scientists scientists proceed – do they rigorously attempt to proceed – do they rigorously attempt to falsify the hypotheses they propose?falsify the hypotheses they propose?

If it isn’t how scientists actually proceed, If it isn’t how scientists actually proceed, what is the justification for the claim that what is the justification for the claim that they they shouldshould proceed this way? proceed this way?