Popper: “Falsifiability is the criterion”Lecture updated!

Why reject verifiability?Why reject verifiability? By then (for reasons we will study shortly), scientists and By then (for reasons we will study shortly), scientists and

philosophers recognized that no empirical theory could philosophers recognized that no empirical theory could ever be proven.ever be proven.

This seemed to take any degree of certainty off the tableThis seemed to take any degree of certainty off the table Moreover, according to Popper, “verifications” or Moreover, according to Popper, “verifications” or

confirmations of a theory were, in many cases, all too easy confirmations of a theory were, in many cases, all too easy to come by.to come by.

‘‘Falsifiability’ is a criterion scientists often site… as do Falsifiability’ is a criterion scientists often site… as do their critics!their critics!

Popper: “Falsifiability is the criterion”

Falsifiability:Falsifiability: Do be scientific, a claim, hypothesis, or theory Do be scientific, a claim, hypothesis, or theory

must be, must be, in principle at least?in principle at least?, falsifiable, falsifiable It must rule out/prohibit some observable (in It must rule out/prohibit some observable (in

principle?) object or event that, principle?) object or event that, if observedif observed, would , would demonstrate the claim, hypothesis or theory is demonstrate the claim, hypothesis or theory is false.false.

If a claim or theory is compatible with all and any If a claim or theory is compatible with all and any states of affairs, it is not falsifiable and thus not states of affairs, it is not falsifiable and thus not scientific (or, as Popper claims” it is “pseudo-scientific (or, as Popper claims” it is “pseudo-scientific”scientific”

Popper: “Falsifiability is the criterion” Exhibit A:Exhibit A:

In court cases decided (in one instance) by the US In court cases decided (in one instance) by the US Supreme Court and by state supreme courts, first Supreme Court and by state supreme courts, first “Creation Science” and, more recently, “Intelligent “Creation Science” and, more recently, “Intelligent Design” were banned from public schools on the Design” were banned from public schools on the grounds that they were not falsifiable, thus not grounds that they were not falsifiable, thus not scientific but rather religion (which can’t be taught in scientific but rather religion (which can’t be taught in public schools).public schools).

Advocates of CS and ID then argued that evolutionary Advocates of CS and ID then argued that evolutionary theory isn’t falsifiable and, thus, not science!theory isn’t falsifiable and, thus, not science!

BTW: is String Theory falsifiable?BTW: is String Theory falsifiable?

Popper: “Falsifiability is the criterion”

His targets:His targets: Adlerian psychologyAdlerian psychology Freudian psychologyFreudian psychology Marxist theoryMarxist theory

What they have in common:What they have in common: Their advocates see confirmations everywhereTheir advocates see confirmations everywhere

Where (I contend) they differ:Where (I contend) they differ: The first two may well be “unfalsifiable”The first two may well be “unfalsifiable” The problem with Marxism (which was falsifiable) was The problem with Marxism (which was falsifiable) was

with its advocates, not the theory itselfwith its advocates, not the theory itself

Popper: “Falsifiability is the criterion”

His targets:His targets: Adlerian psychologyAdlerian psychology Freudian psychologyFreudian psychology

What renders them “unfalsifiable”?What renders them “unfalsifiable”? Not the uncritical attitude of their advocatesNot the uncritical attitude of their advocates The second has a “protective belt” that effectively The second has a “protective belt” that effectively

repels all counter-evidencerepels all counter-evidence The first is simply compatible with any way an agent The first is simply compatible with any way an agent

behaves!behaves!

Popper: “Falsifiability is the criterion”

Popper has logic on his side; for while no Popper has logic on his side; for while no empirical theory can be proven, any (genuinely) empirical theory can be proven, any (genuinely) empirical theory can be empirical theory can be disprovendisproven and, at least in and, at least in principle, by principle, by justjust oneone failed experiment or failed experiment or prediction, by prediction, by just onejust one observation. observation.

The logic of confirmation vs. the logic of The logic of confirmation vs. the logic of falsificationfalsification

1.1. If If HH, then , then II

2.2. II

------------------------------------

HH

Logic of confirmation: Logic of confirmation:

Affirming the consequentAffirming the consequent

Deductively invalidDeductively invalid

1.1. If If HH, then , then II

2.2. Not Not II

------------------------------------

Not Not HH

Logic of falsificationLogic of falsification

Modus TollensModus Tollens

Deductively valid.Deductively valid.

The Mind’s Big Bang

The Paleolithic period (or Old Stone Age) is the earliest The Paleolithic period (or Old Stone Age) is the earliest period of human development. Dating from about 2 period of human development. Dating from about 2 million years ago, and ending in various places between million years ago, and ending in various places between 50,000 and 10,000 years ago, it is roughly co-extensive 50,000 and 10,000 years ago, it is roughly co-extensive with the geologic period known as the Pleistocene [some with the geologic period known as the Pleistocene [some would update timeline]would update timeline]

An epoch which was marked by continuous cooling, An epoch which was marked by continuous cooling, which resulted in several ice ages. During the period, which resulted in several ice ages. During the period, hominids become increasingly advanced in terms of fire hominids become increasingly advanced in terms of fire and tool making, and modern humans emerge.and tool making, and modern humans emerge.

The Mind’s Big Bang

Evidence of Cro-Magnon humans (one of several varieties Evidence of Cro-Magnon humans (one of several varieties of modern humans that lived during the period) indicates of modern humans that lived during the period) indicates they lived some 50,000-10,000 years ago. Anatomically they lived some 50,000-10,000 years ago. Anatomically the same as today’s the same as today’s Homo sapiensHomo sapiens and fossil remains, and fossil remains, graves, artifacts, and dwellings have been found graves, artifacts, and dwellings have been found throughout Europe.throughout Europe.

It is believed that their arrival in Europe, when they It is believed that their arrival in Europe, when they encountered another hominid species, the Neanderthals, encountered another hominid species, the Neanderthals, resulted in the extinction of the latter.resulted in the extinction of the latter.

In a recent article in “The Science Times,” it was In a recent article in “The Science Times,” it was hypothesized that Cro-Magnons were so startled to be hypothesized that Cro-Magnons were so startled to be confronted with another bi-pedal, tool using (and much confronted with another bi-pedal, tool using (and much larger!) hominid, that they developed the practice of larger!) hominid, that they developed the practice of designing beads that would identify them. designing beads that would identify them.

The Mind’s Big Bang The discovery of decorative beadsThe discovery of decorative beads Differences in the treatment that humans and Neanderthals provided Differences in the treatment that humans and Neanderthals provided

the deadthe dead Cave paintingsCave paintings Fossil evidence (particularly skulls) of differences between Fossil evidence (particularly skulls) of differences between

Neanderthals and humansNeanderthals and humans Relatively quick innovations (in, for example, spears and spear Relatively quick innovations (in, for example, spears and spear

heads)heads) Migrations of early humans across EuropeMigrations of early humans across Europe Cave instruments and musicCave instruments and music Biological changes in the brainBiological changes in the brain Comparison of humans and chimpanzeesComparison of humans and chimpanzees The emergence and significance of languageThe emergence and significance of language Cultural forces overriding biological forcesCultural forces overriding biological forces

Popper: “Falsifiability is the criterion”

Although it was unclear at the time whether Einstein’s Although it was unclear at the time whether Einstein’s theory was true, it turns out to be scientific on Popper’s theory was true, it turns out to be scientific on Popper’s view.view.

Eddington’s experiment:Eddington’s experiment: Einstein’s theories predicted that light, like material objects, is Einstein’s theories predicted that light, like material objects, is

subject to the gravitational “pull” of large objectssubject to the gravitational “pull” of large objects Hypothesis: light traveling from a star that is located “behind” Hypothesis: light traveling from a star that is located “behind”

the sun from the perspective of the Earth should bend as it passes the sun from the perspective of the Earth should bend as it passes the sunthe sun

A bold hypothesis and one that would take years to carry out. A bold hypothesis and one that would take years to carry out. Scientists had to wait for a solar eclipse so that a star’s light Scientists had to wait for a solar eclipse so that a star’s light would be visiblewould be visible

Eddington’s experiment

A reconstruction of what Eddington’s A reconstruction of what Eddington’s photographs demonstrated:photographs demonstrated:

Eddington’s experiment

Again, it was not the confirmation of Relativity Again, it was not the confirmation of Relativity that struck Popper, but its that struck Popper, but its falsifiability and falsifiability and boldnessboldness: even before Eddington’s experiment : even before Eddington’s experiment confirmed it, scientists knew what would, in confirmed it, scientists knew what would, in principle, falsify the hypothesis: namely, not principle, falsify the hypothesis: namely, not observing the bending of the light traveling from observing the bending of the light traveling from the star toward Earth.the star toward Earth.

Moreover, confirmations of a theory should only Moreover, confirmations of a theory should only count as significant when the theory in question is count as significant when the theory in question is bold…bold…

Falsifiability

Marxism is rendered pseudo-scientific Marxism is rendered pseudo-scientific notnot because the original theory was not falsifiable.because the original theory was not falsifiable.

Marx and Engel’s claims about upcoming Marx and Engel’s claims about upcoming proletariat revolutions in capitalist societies were proletariat revolutions in capitalist societies were falsifiable, and in most cases, falsifiable, and in most cases, falsifiedfalsified..

But advocates of Marxism, in efforts to save the But advocates of Marxism, in efforts to save the theory from the falsifications, introduce theory from the falsifications, introduce Ad hocAd hoc hypotheses to save it.hypotheses to save it.

Ad hocAd hoc: From the Latin “for this purpose” (in this : From the Latin “for this purpose” (in this case, saving the theory…)case, saving the theory…)

Things we will later consider…

The difference between a theory actually being un-The difference between a theory actually being un-falsifiable, by its nature or structure, and a theory’s falsifiable, by its nature or structure, and a theory’s advocates resorting to advocates resorting to ad hocad hoc hypotheses to save it. hypotheses to save it.

Isn’t it possible that a genuinely scientific theory will Isn’t it possible that a genuinely scientific theory will be confirmed repeatedly and no counter-examples be confirmed repeatedly and no counter-examples encountered?encountered?

The “in principle” caveat is important. “There is a The “in principle” caveat is important. “There is a little red school house on the dark side of Jupiter” is little red school house on the dark side of Jupiter” is sillysilly but but falsifiable in principle.falsifiable in principle.

How easy or straightforward is it to identify added How easy or straightforward is it to identify added hypotheses that ARE hypotheses that ARE ad hocad hoc, but added hypotheses , but added hypotheses that are NOT that are NOT ad hocad hoc (i.e., are defensible) (i.e., are defensible)