Popper: 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” or naïve, and Hempel’s “sophisticated” version of or naïve, and Hempel’s “sophisticated” version of inductivism).inductivism). 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.

Popper’s explication and defense of falsification

The rejection of “psychologism” The question of how an idea (hypothesis) occurs to The question of how an idea (hypothesis) occurs to

a person may be of interest to psychologists, but not a person may be of interest to psychologists, but not to those interested in the logical analysis of scientific to 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 matters of fact; the The former is concerned with matters of fact; the latter concerned with questions of justification or latter concerned with questions of justification or validity – i.e., is normative rather than descriptivevalidity – i.e., is normative rather than descriptive

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

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 FalsificationismStages 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?

Popper’s FalsificationismLet’s start with the empirical question:Let’s start with the empirical question:Of the scientists we’ve read, read about, or Of the scientists we’ve read, read about, or

seen in films, do they seem hell bent to seen in films, do they seem hell bent to disprove their own hypotheses and disprove their own hypotheses and theories? Granted they test them (when theories? Granted they test them (when they can) but is this to falsify them and they can) but is this to falsify them and move on to “better” hypotheses or move on to “better” hypotheses or theories?theories?

And what of the historical cases we’ve And what of the historical cases we’ve considered? If Falsificationism is supposed considered? If Falsificationism is supposed to be how scientists reason, do these to be how scientists reason, do these cases support the account?cases support the account?

Popper’s Falsificationism The scientific reaction to:The scientific reaction to:

The case of planetary misbehavior and its The case of planetary misbehavior and its challenge to Newtonian theorychallenge to Newtonian theory

The scientific reaction to apparent falsifiers of The scientific reaction to apparent falsifiers of the Copernican hypothesis (stellar parallax the Copernican hypothesis (stellar parallax which it predicted is not observed)which it predicted is not observed)

Two more examples:Two more examples: Darwin took the bright colors, larger size, Darwin took the bright colors, larger size,

antlers, and other “ornaments” of many males antlers, and other “ornaments” of many males in a species as potentially falsifying his theory in a species as potentially falsifying his theory of natural selection.of natural selection.

He viewed them as inhibiting survival, rather He viewed them as inhibiting survival, rather than enhancing it or being “benign” in terms of than enhancing it or being “benign” in terms of it.it.

Popper’s Falsificationism Darwin took the bright colors, larger size, antlers, Darwin took the bright colors, larger size, antlers,

and “ornaments” of many males in a species as and “ornaments” of many males in a species as potentially falsifying his theory of natural potentially falsifying his theory of natural selection.selection.

Why? They not only seemed not to enhance survival, Why? They not only seemed not to enhance survival, but to act directly against it. but to act directly against it.

Did he abandon natural selection?Did he abandon natural selection? No, he proposed the hypothesis of sexual No, he proposed the hypothesis of sexual

selection as a secondary evolutionary force that selection as a secondary evolutionary force that enhances reproductive success:enhances reproductive success:

1.1. Male-male competition for (relatively scarce) femalesMale-male competition for (relatively scarce) females2.2. Female choice of mates who had such ornamentationFemale choice of mates who had such ornamentation

Popper’s Falsificationism The “co-discover” of natural selection, The “co-discover” of natural selection,

Wallace, was horrified by Darwin’s new Wallace, was horrified by Darwin’s new hypothesis, maintaining it washypothesis, maintaining it was

Ad hoc (Added simply to save the theory)Ad hoc (Added simply to save the theory) Violated the norm that a genuine theory of Violated the norm that a genuine theory of

evolution would have one and only one evolution would have one and only one explanation or mechanismexplanation or mechanism

A good Victorian, he found the notion of A good Victorian, he found the notion of “female choice” and its having long term “female choice” and its having long term consequences at least unappealing if not consequences at least unappealing if not ludicrous.ludicrous.

Popper’s Falsificationism As Darwin noted in his chapter “Difficulties As Darwin noted in his chapter “Difficulties

on theory” towards the conclusion of on theory” towards the conclusion of The The OriginOrigin, there were many:, there were many:

A lack of fossil evidence for the “innumerable A lack of fossil evidence for the “innumerable transitional forms” his understanding of natural transitional forms” his understanding of natural selection entailedselection entailed

A lack of a theory of inheritance (how parents A lack of a theory of inheritance (how parents tend to pass on traits to their offspring)tend to pass on traits to their offspring)

How can one and same process, natural How can one and same process, natural selection, produce “trifling” organs (a giraffe’s selection, produce “trifling” organs (a giraffe’s tail which is but a fly swatter) and astounding tail which is but a fly swatter) and astounding and seeming perfect organs (the eye)?and seeming perfect organs (the eye)?

Popper’s Falsificationism These problems (and they are just a few of These problems (and they are just a few of

those that Darwin identified) were not taken those that Darwin identified) were not taken as falsifying the theory (or even rendering it as falsifying the theory (or even rendering it unscientific) by Darwin or many of his unscientific) by Darwin or many of his scientific contemporariesscientific contemporaries

They were seen, instead, as among those They were seen, instead, as among those research problemsresearch problems that the emerging that the emerging discipline of evolutionary theory would discipline of evolutionary theory would tackle, while assuming that the overall tackle, while assuming that the overall theory of natural selection is correct.theory of natural selection is correct.

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 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 But the Copernican model But the Copernican model alsoalso had to had to

include epicycles to make it compatible 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 It was not until Kepler recognized that the planets’ orbits are elliptical that planets’ orbits are elliptical that astronomers no longer needed epicycles.astronomers no longer needed epicycles.

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.

Popper’s Falsificationism So, at least some historical episodes (and So, at least some historical episodes (and

actual current scientific practices) actual current scientific practices) challenge the notion that Falsificationism challenge the notion that Falsificationism isis the form of reasoning and the purpose of the form of reasoning and the purpose of testing in which scientists engage.testing in which scientists engage.

So what kind of model is it? And what So what kind of model is it? And what justifies it?justifies it?

Is it an attempt at “rational reconstruction” Is it an attempt at “rational reconstruction” of actual scientific practices?of actual scientific practices?

Is it a normative claim that, however Is it a normative claim that, however scientists actually behave, they scientists actually behave, they shouldshould embrace Falsificationism as their method?embrace Falsificationism as their method?

Popper’s Falsificationism Efforts in the philosophy of science to “rationally Efforts in the philosophy of science to “rationally

reconstruct” actual scientific practice are typically reconstruct” actual scientific practice are typically designed to show that some apparent designed to show that some apparent commitment (for example, to non-observables or commitment (for example, to non-observables or to saving a theory from refutation) can be to saving a theory from refutation) can be reconstructed by philosophers to show how such reconstructed by philosophers to show how such commitments aren’t necessary to the science in commitments aren’t necessary to the science in question or its success. question or its success.

This means imposing philosophical normative This means imposing philosophical normative notions (what is rational) on scientific practice to, notions (what is rational) on scientific practice to, in effect, “retell the episode” so as to preserve a in effect, “retell the episode” so as to preserve a favored view of what is rational.favored view of what is rational.

Popper’s Falsificationism Is Popper engaged in this?Is Popper engaged in this? Or is he laying out a model of how Or is he laying out a model of how

scientists scientists should behaveshould behave in practice? in practice? If the latter, does the model have what it If the latter, does the model have what it

needs to explain the developments, needs to explain the developments, trajectories, and at least apparent trajectories, and at least apparent successes of various sciences in various successes of various sciences in various historical periods?historical periods?

Would it have been more rational or Would it have been more rational or scientific to reject the Copernican scientific to reject the Copernican hypothesis? Or Darwin’s natural selection?hypothesis? Or Darwin’s natural selection?

Popper’s Falsificationism On the other side, Popper’s model seems On the other side, Popper’s model seems

to many bench scientists reflective of:to many bench scientists reflective of: Their commitment to fallibilismTheir commitment to fallibilism Their rejection of dogmatismTheir rejection of dogmatism Their willingness, when and as appropriate, to Their willingness, when and as appropriate, to

abandon a long-standing theory when the abandon a long-standing theory when the evidence mounts up against it.evidence mounts up against it.

As an example, many who have testified or As an example, many who have testified or written against “Creation Science” and/or written against “Creation Science” and/or ID, cite falsifiability as something the latter ID, cite falsifiability as something the latter lack, and the 3 commitments above as lack, and the 3 commitments above as what distinguishes science from CS and IDwhat distinguishes science from CS and ID

Popper’s Falsificationism One possibility: Popper’s model is both One possibility: Popper’s model is both

empirical (in keeping with actual scientific empirical (in keeping with actual scientific practice) practice) andand normative (a prescription of normative (a prescription of how scientists how scientists ought to behaveought to behave

Popper takes Popper takes scientific revolutions scientific revolutions as the as the “norm”, providing the most important “norm”, providing the most important empirical examples from which the most empirical examples from which the most important normative conclusions can be important normative conclusions can be drawn (but he may be wrong…)drawn (but he may be wrong…)

But what if revolutions in science are But what if revolutions in science are rarerare and thus do yield the best understandings and thus do yield the best understandings of most of (the bulk of) actual scientific of most of (the bulk of) actual scientific practice?practice?

Popper’s Falsificationism To return, briefly, to the issue of “Ad hoc To return, briefly, to the issue of “Ad hoc

hypotheses” (which, by the way, scientists hypotheses” (which, by the way, scientists often charge creationists with appealing to often charge creationists with appealing to in order to save their “theory” in light of in order to save their “theory” in light of numerous counterexamples).numerous counterexamples).

We used the case of “planetary We used the case of “planetary misbehavior” to raise the issue of whether misbehavior” to raise the issue of whether it is always unwarranted (non-scientific) to it is always unwarranted (non-scientific) to supplement a theory with an additional supplement a theory with an additional hypothesis to explain an apparent hypothesis to explain an apparent counterexample, and whether it is possible counterexample, and whether it is possible to know if a hypothesis is ad hoc at the to know if a hypothesis is ad hoc at the time it is proposed, or only in hindsight.time it is proposed, or only in hindsight.

Popper’s Falsificationism But aren’t there instances where we might think a But aren’t there instances where we might think a

hypothesis is “ad hoc” even before it’s tested.hypothesis is “ad hoc” even before it’s tested. A different (in this case, imaginary) episode A different (in this case, imaginary) episode

involving planetary misbehaviorinvolving planetary misbehavior Suppose that no new planet Suppose that no new planet p’p’ is discovered that is discovered that

explains the orbit of explains the orbit of pp in a way consistent with in a way consistent with Newton’s theories…Newton’s theories…

And our scientist proposes that the previously And our scientist proposes that the previously undiscovered planet is too small for today’s undiscovered planet is too small for today’s telescopes to be able to seetelescopes to be able to see

So she applies for a grant to build a stronger So she applies for a grant to build a stronger telescope and in three years time it is ready…telescope and in three years time it is ready…

The telescope is trained to that part of the sky The telescope is trained to that part of the sky where where p’p’ should be… but it doesn’t seem to be. should be… but it doesn’t seem to be.

Popper’s Falsificationism Does our scientist give up on the existence of Does our scientist give up on the existence of

this not yet discovered planet?this not yet discovered planet? No, she proposes that a cloud of magnetic dust No, she proposes that a cloud of magnetic dust

hides the planet from us. She calculates the hides the planet from us. She calculates the location and properties of this cloud, and applies location and properties of this cloud, and applies for a research grant to send a satellite up to for a research grant to send a satellite up to check to see if she is right about the cloud.check to see if she is right about the cloud.

Were the satellite’s instruments (perhaps brand Were the satellite’s instruments (perhaps brand new just for this mission) to detect the cloud, new just for this mission) to detect the cloud, this would be hailed as a victory…this would be hailed as a victory…

But if not...? When does one give up?But if not...? When does one give up?

Popper’s Falsificationism Is the determination of “falsification” relative to Is the determination of “falsification” relative to

the level of previous success a theory enjoyed the level of previous success a theory enjoyed and/or the scientific community’s judgment?and/or the scientific community’s judgment?

Is the logic of falsification aptly a description of Is the logic of falsification aptly a description of reasoning in a scientific revolution, but not when reasoning in a scientific revolution, but not when science is not ready for/expecting a revolution?science is not ready for/expecting a revolution?

Modus Tollens is a deductively valid argument Modus Tollens is a deductively valid argument form, but what does the role of auxiliary form, but what does the role of auxiliary assumptions, plus the inference “If H, then (if C, assumptions, plus the inference “If H, then (if C, then E), suggest about all that it presupposes then E), suggest about all that it presupposes and, thus, its limits?and, thus, its limits?