Lecture 8 1. More mental gymnastics 2. Tales from the history of science 3. Popper’s “solution” to the problem of induction 4. Which of two possible conclusions about scientific reasoning is Popper actually arguing for? 5. Is either argument successful?

On a distant island, there are 3 kinds of humans: Knights, Knaves, and Normals. Knights always tell the truth. Knaves always lie. Normals sometimes lie and sometimes tell the truth. Detectives investigating a crime questioned 3 inhabitants, A, B, and C of the island. They knew one of them had committed the crime, but not which one. They also knew that the criminal was a Knight, and that the other two they questioned were not. The investigators made a transcript of the statements made by each of the 3 inhabitants. Using logic, did they identify A, B, or C as the guilty person?

On a distant island, there are 3 kinds of humans: Knights, Knaves, and Normals. A: I am innocent B: That is true. C: B is not a normal. Which one is the Knight and, therefore, the criminal? Identify the possible solutions. Identify the fact list. Evaluate the possible solutions given the fact list (which includes what each said) and solve the puzzle

A: I am innocent. If A is the Knight, … B: That is true. If B is lying, … C: B is not normal. If C is lying, …

Popper: Falsificationism  From “falsifiability” as the criterion that distinguishes science from “pseudo-science” to “falsificationism” as a model of scientific method/reasoning.  A rejection of all forms of inductivism (both “narrow” and Hempel’s “sophisticated” version).  There is no “principle of induction” that will justify induction or an inductivist account of scientific method/reasoning  Like Hempel, Popper emphasizes that there is no logic of discovery, but only a logic of justification (testing)  But, unlike Hempel, Popper argues that the logic involved in the context of justification or testing is deductive and specifically the logic of falsification.

Part 2 Tales from the history of science

Cases of planetary misbehavior A physicist of the Newtonian era took Newton’s law of gravitation, N, the accepted initial conditions, C, and calculated the predicted path of the planet, Uranus. But the planet deviated from the calculated path. Did our Newtonian physicist consider, that once established, the deviation of Uranus from its predicated path refutes the law, N?

Well, yes, a few did. But more proposed that there was another, yet undiscovered planet whose gravitational pull explained the deviation in Uranus’ predicted path. Using Newtonian theory, they predicted where the planet would be, its mass, etc. Was this prediction Ad hoc? How might we be able to decide if it was? In this case, when they trained telescopes to the predicted region of the sky, they discovered the planet Neptune and claimed a victory for Newtonian theory! Because Neptune’s predicted path also deviated from what was predicted, they proposed another planet… and discovered Pluto!

Cases of planetary misbehavior

Uh, oh! What to do about the peacock’s tail?  As Darwin understood things, Natural Selection cannot “select” a trait that is disadvantageous to its bearer – that compromises its survival  So what to do with all the “ornaments” that (predominantly) male members of various species are endowed?  The Peacock’s tail  Antlers  Bright colors…

Uh, oh! What to do about the peacock’s tail?  It seemed that many such traits were not “benign” but actually put those so endowed at a distinct disadvantage  It’s very hard for a peacock to take off, fly easily, and land  Young males with antlers often crash into trees, each other, buildings, and so forth  Bright colors seem to make an organism an easier target for prey  Apparent counter-examples to or falsifiers of evolution by Natural Selection!

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

Popper’s Falsificationism  One problem facing the Aristotelian and Ptolemaic model of astronomy (geocentrism) was its complicatedness (or what today’s physicists might describe as its ‘inelegance’).  Because it assumed that planets move in a uniform, circular motion and at a uniform speed, it had to contend with (among other observations) the apparent “retrograde motion” of some planets. Mars, for example, seems at times of the year to stop and go in reverse for awhile before resuming its regular circular motion…

Popper’s Falsificationism  But, although this was seen as a major flaw with the geocentric model, the Copernican model, also had to include epicycles to make it compatible with apparent retrograde motion of planets – albeit, somewhat less.  It was not until Kepler recognized that the planets’ orbits are elliptical that astronomers no longer needed epicycles.

Popper’s Falsificationism  To address the problem, astronomers added “epicycles” to planetary orbits:  Smaller (but still circular!) orbits compatible with apparent retrograde motion…  As the story goes, the Copernican hypothesis was much simpler and superior.

Popper’s Falsificationism  The moral: if the need for epicycles was taken to be a reason to reject the geocentric model, it was not solved (initially) by the Copernican model – but scientists accepted the latter anyway.

Part 3 Popper’s “solution” to The problem of induction

Popper’s explication and defense of falsificationism 1. Reiterate (in contemporary terms) why inductive reasoning cannot be justified. 1. To justify it would require “a principle of induction”, itself known a priori or being the conclusion of a sound argument. We do not and cannot have either. 2. Even a probabilistic understanding of inductive reasoning would require its own “principle of induction”, and suffers from the same problems. 3. So if (as Hume claimed) it might turn out that psychologists report scientists (and the rest of us) use induction, this is not itself an epistemological issue.

Popper’s explication and defense of falsificationism 2. Reject “psychologism”  The question of how an idea (hypothesis) occurs to a person may be of interest to psychologists, but not to those interested in the logical analysis of scientific reasoning (i.e., in the epistemology of science).  The former is concerned with description ; the latter concerned with questions of justification or validity – i.e., is normative rather than descriptive 3. Reiterate the discovery/justification distinction: However a scientist arrives at a hypothesis, all that philosophy of science (epistemology) is concerned with is whether the hypothesis is justified.

4. Provide an alternative to inductivist accounts of scientific reasoning and, in particular, a deductivist account of the testing of hypotheses. 1. Make use of the fact that while the logic of confirmation involves a deductively invalid argument form, and is beset by the (old?) problem of induction, the logic of falsification involves a deductively valid argument form and avoids the problem of induction altogether. If H, then I Not I Not H

Popper’s Falsificationism  The tests any proposed hypothesis is (or should be?) subjected to:  Internal consistency: does it include any logical contradictions/inconsistencies?  Is it actually scientific, i.e., falsifiable?  External consistency: is it consistent with relevant theories that are currently accepted?  How does it fare when it is tested?  So long as a theory avoids being falsified, we say it is corroborated (weaker than ‘confirmed’).  There is no inductive reasoning involved here!

Popper’s Falsificationism Stages in scientific reasoning (as it is or as it should be?) 1. Bold conjectures [they go out on a limb, prohibit the occurrence of some set of phenomena (events, objects, and so forth)]. 2. Rigorous efforts to falsify the hypothesis by subjecting it to tests. 3. Falsification (or corroboration). If the first, rejection of the hypotheses and search for and 4. The emergence of a new bold conjecture… proceed to steps 2, 3 and 4…

Popper’s FalsificationismQuestions: If we reject psychologism (the study of how scientists actually think and reason), is Falsificationism itself an empirical account of how they do or an account of how, ideally, they should reason? If the former, is it in fact how scientists proceed – do they rigorously attempt to falsify the hypotheses they propose? If it isn’t how scientists actually proceed, what is the justification for the claim that they should proceed this way?