Popper: Falsificationism

1. 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” or naïve, and Hempel’s “sophisticated” version of inductivism). • 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.

2. Popper’s explication and defense of falsification • The rejection of “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 matters of fact; the latter concerned with questions of justification or validity – i.e., is normative rather than descriptive • Discovery/justification: However a scientist arrives at a hypothesis, all that philosophy of science (epistemology) is concerned with is whether the hypothesis is justified.

3. 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!

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

5. Popper’s Falsificationism Questions: 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?

6. Popper’s Falsificationism Let’s start with the empirical question: Of the scientists we’ve read, read about, or seen in films, do they seem hell bent to disprove their own hypotheses and theories? Granted they test them (when they can) but is this to falsify them and move on to “better” hypotheses or theories? And what of the historical cases we’ve considered? If Falsificationism is supposed to be how scientists reason, do these cases support the account?

7. Popper’s Falsificationism • The scientific reaction to: • The case of planetary misbehavior and its challenge to Newtonian theory • The scientific reaction to apparent falsifiers of the Copernican hypothesis (stellar parallax which it predicted is not observed) • Two more examples: • Darwin took the bright colors, larger size, antlers, and other “ornaments” of many males in a species as potentially falsifying his theory of natural selection. • He viewed them as inhibiting survival, rather than enhancing it or being “benign” in terms of it.

8. Popper’s Falsificationism • Darwin took the bright colors, larger size, antlers, and “ornaments” of many males in a species as potentially falsifying his theory of natural selection. • Why? They not only seemed not to enhance survival, but to act directly against it. • Did he abandon natural selection? • No, he proposed the hypothesis of sexual selection as a secondary evolutionary force that enhances reproductive success: • Male-male competition for (relatively scarce) females • Female choice of mates who had such ornamentation

9. Popper’s Falsificationism • The “co-discover” of natural selection, Wallace, was horrified by Darwin’s new hypothesis, maintaining it was • Ad hoc (Added simply to save the theory) • Violated the norm that a genuine theory of evolution would have one and only one explanation or mechanism • A good Victorian, he found the notion of “female choice” and its having long term consequences at least unappealing if not ludicrous.

10. Popper’s Falsificationism • As Darwin noted in his chapter “Difficulties on theory” towards the conclusion of The Origin, there were many: • A lack of fossil evidence for the “innumerable transitional forms” his understanding of natural selection entailed • A lack of a theory of inheritance (how parents tend to pass on traits to their offspring) • How can one and same process, natural selection, produce “trifling” organs (a giraffe’s tail which is but a fly swatter) and astounding and seeming perfect organs (the eye)?

11. Popper’s Falsificationism • These problems (and they are just a few of those that Darwin identified) were not taken as falsifying the theory (or even rendering it unscientific) by Darwin or many of his scientific contemporaries • They were seen, instead, as among those research problems that the emerging discipline of evolutionary theory would tackle, while assuming that the overall theory of natural selection is correct.

12. 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…

13. 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.

14. Popper’s Falsificationism • But 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.

15. 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.

16. Popper’s Falsificationism • So, at least some historical episodes (and actual current scientific practices) challenge the notion that Falsificationism is the form of reasoning and the purpose of testing in which scientists engage. • So what kind of model is it? And what justifies it? • Is it an attempt at “rational reconstruction” of actual scientific practices? • Is it a normative claim that, however scientists actually behave, they should embrace Falsificationism as their method?

17. Popper’s Falsificationism • Efforts in the philosophy of science to “rationally reconstruct” actual scientific practice are typically designed to show that some apparent commitment (for example, to non-observables or to saving a theory from refutation) can be reconstructed by philosophers to show how such commitments aren’t necessary to the science in question or its success. • This means imposing philosophical normative notions (what is rational) on scientific practice to, in effect, “retell the episode” so as to preserve a favored view of what is rational.

18. Popper’s Falsificationism • Is Popper engaged in this? • Or is he laying out a model of how scientists should behave in practice? • If the latter, does the model have what it needs to explain the developments, trajectories, and at least apparent successes of various sciences in various historical periods? • Would it have been more rational or scientific to reject the Copernican hypothesis? Or Darwin’s natural selection?

19. Popper’s Falsificationism • On the other side, Popper’s model seems to many bench scientists reflective of: • Their commitment to fallibilism • Their rejection of dogmatism • Their willingness, when and as appropriate, to abandon a long-standing theory when the evidence mounts up against it. • As an example, many who have testified or written against “Creation Science” and/or ID, cite falsifiability as something the latter lack, and the 3 commitments above as what distinguishes science from CS and ID

20. Popper’s Falsificationism • One possibility: Popper’s model is both empirical (in keeping with actual scientific practice) and normative (a prescription of how scientists ought to behave • Popper takes scientific revolutions as the “norm”, providing the most important empirical examples from which the most important normative conclusions can be drawn (but he may be wrong…) • But what if revolutions in science are rare and thus do yield the best understandings of most of (the bulk of) actual scientific practice?

21. Popper’s Falsificationism • To return, briefly, to the issue of “Ad hoc hypotheses” (which, by the way, scientists often charge creationists with appealing to in order to save their “theory” in light of numerous counterexamples). • We used the case of “planetary misbehavior” to raise the issue of whether it is always unwarranted (non-scientific) to supplement a theory with an additional hypothesis to explain an apparent counterexample, and whether it is possible to know if a hypothesis is ad hoc at the time it is proposed, or only in hindsight.

22. Popper’s Falsificationism • But aren’t there instances where we might think a hypothesis is “ad hoc” even before it’s tested. • A different (in this case, imaginary) episode involving planetary misbehavior • Suppose that no new planet p’ is discovered that explains the orbit of p in a way consistent with Newton’s theories… • And our scientist proposes that the previously undiscovered planet is too small for today’s telescopes to be able to see • So she applies for a grant to build a stronger telescope and in three years time it is ready… • The telescope is trained to that part of the sky where p’ should be… but it doesn’t seem to be.

23. Popper’s Falsificationism • Does our scientist give up on the existence of this not yet discovered planet? • No, she proposes that a cloud of magnetic dust hides the planet from us. She calculates the location and properties of this cloud, and applies for a research grant to send a satellite up to check to see if she is right about the cloud. • Were the satellite’s instruments (perhaps brand new just for this mission) to detect the cloud, this would be hailed as a victory… • But if not...? When does one give up?

24. Popper’s Falsificationism • Is the determination of “falsification” relative to the level of previous success a theory enjoyed and/or the scientific community’s judgment? • Is the logic of falsification aptly a description of reasoning in a scientific revolution, but not when science is not ready for/expecting a revolution? • Modus Tollens is a deductively valid argument form, but what does the role of auxiliary assumptions, plus the inference “If H, then (if C, then E), suggest about all that it presupposes and, thus, its limits?