Popper, Falsification and Scientific Demarcation

Karl Popper

 

Falsification, not induction

Sir Karl Popper: 1902-1994

 

The Problem of Demarcation

 

Science was a game which required that in some specifiable circumstances we reject a given scientific theory.

 

For Popper, other sorts of theory could perfectly well be meaningful, but they are not scientific. 

So Popper was not a “commit it to the flames” sort of guy.

 

This was first offered as a logical feature of the theory, that is, what is MEANT by “science, ad that which serves to distinguish instances of science from, say, instances of metaphysics or pseudo-science.

 

A scientific theory must have implications for observation, and when our observations show those implications are false, we can reject the theory.

 

But notice, if we were to adopt the criterion of verification as is, then scientific statements would be no less meaningless than metaphysical statements since neither statements are verifiable.

 

Science is not distinguished from non-science on basis of methodology.  No unique methodology specific to science

Science consists mostly of problem solving.

A demarcation between science and pseudo-science is established by falsification.  A theory is scientific only if it is refutable by a the observation of a conceivable event.

 

Every genuine test of a scientific theory is based on an asymmetry between verification and falsification

 

Falsification is the idea that science

 

1. advances by unjustified, exaggerated guesses followed by

2. unrelenting criticism

 

Any "positive support" for theories is both unobtainable and superfluous.

 

All we can and need do is create theories and eliminate error.

Scientists never actually use induction according to Popper.  It is impossible to verify propositions by reference to experience. 

This is his “answer” to the “problem of induction.”

 

Good scientific practice: E.g. Einstein’s general relativity

 

Probably the most important eclipse in the history of science occurred on 29 May 1919. Just six months after the end of World War I, British astronomers used it to test a new idea that came from Germany in 1915.

 

The proposition was that gravity affected light, space and time itself, and as a result the Sun would deflect starlight passing by it. Changes in the apparent direction of stars in the sky, seen close to the Sun during a total eclipse, could confirm the idea.

 

The announcement of favourable results in London on 8 November 1919 signalled the replacement of Newton's theory of gravity by the theory of general relativity. Its originator, a 40-year old Berliner called Albert Einstein, at once became the most famous scientist in the world.

 

Expeditions of astronomers photographed the eclipse in difficult tropical conditions in Brazil and on the African island of Principe. At the time, the Sun was in front of a useful cluster of stars, the Hyades. The astronomers compared the relative positions in the sky near the Sun with the positions of the same stars as previously photographed in the night sky.

 

The expeditions and analyses, organised by the Royal Society and the Royal Astronomical Society, were masterminded by Arthur Eddington of Cambridge. He was one of the very few experts who immediately understood Einstein's theory and appreciated its revolutionary importance, if it was correct.

 

Even for stars almost in line with the Sun, the shift in apparent position is less than two seconds of arc, or a few ten-thousandths of a degree. The 1919 measurements confirmed that the Sun bent the light rays by roughly the right extent - less than predicted in Principe, more than predicted in Brazil.[1]

 

Conjecture: mass of the sun bends the path of light

 

·         If the apparent location of the observed star doesn’t shift, the theory is wrong.

·         It will have been refuted.

 

So the mark of a scientific theory is whether it can be falsified by observation

 

“Falsificationists… prefer an attempt to solve an interesting problem by a bold conjecture, even (and especially) if it soon turns out to be false, to any recital of a sequence of irrelevant truisms”(CR: 231)

 

This gives us:

 

(i)                  a glimpse of scientific method

(ii)                a demarcation criterion for science

 

Scientific method:

 

·         Scientific theories have deductive consequences

·         They can be falsified but not confirmed.

·         The objective of scientific theorizing is to put forward (bold) hypotheses and then test them in order to falsify them

·         Theories are falsified by basic statements[2]

(what is a basic statement?)

Confirmation and Pseudoscience

 

Demarcation:

 

So scientific theories are those that can be falsified by basic statements. (pace Quine)

Good scientific theories do not make themselves immune from falsification by use of ad hoc hypotheses. 

 

Progress of Science:

 

Science progresses by eliminating theories that have been falsified.

 

But.. does this in fact constitute process?  Falsifying one of finitely many potentially true theories might be thought to constitute progress, like find one losing lottery ticket my narrow the field of potential winners, but eliminating one of infinitely many possibly true theories does not seem to qualify are making progress to the “truth.”

 

A scientific theory cannot be shown to be true. But some scientific theories do have varying degrees of success. They resist falsification.

 

The difficulties connected with my criterion of demarcation (D) are important, but must not be exaggerated. It is vague, since it is a methodological rule, and since the demarcation between science and nonscience is vague. But it is more than sharp enough to make a distinction between many physical theories on the one hand, and metaphysical theories, such as psychoanalysis, or Marxism (in its present form), on the other. This is, of course, one of my main theses; and nobody who has not understood it can be said to have understood my theory.

 

The situation with Marxism is, incidentally, very different from that with psychoanalysis. Marxism was once a scientific theory: it predicted that capitalism would lead to increasing misery and, through a more or less mild revolution, to socialism; it predicted that this would happen first in the technically highest developed countries; and it predicted that the technical evolution of the 'means of production' would lead to social, political, and ideological developments, rather than the other way round.

 

But the (so-called) socialist revolution came first in one of the technically backward countries. And instead of the means of production producing a new ideology, it was Lenin's and Stalin's ideology that Russia must push forward with its industrialization ('Socialism is dictatorship of the proletariat plus electrification') which promoted the new development of the means of production.

 

Thus one might say that Marxism was once a science, but one which was refuted by some of the facts which happened to clash with its predictions (I have here mentioned just a few of these facts).

 

However, Marxism is no longer a science; for it broke the methodological rule that we must accept falsification, and it immunized itself against the most blatant refutations of its predictions. Ever since then, it can be described only as nonscience—as a metaphysical dream, if you like, married to a cruel reality.

 

Psychoanalysis is a very different case. It is an interesting psychological metaphysics (and no doubt there is some truth in it, as there is so often in metaphysical ideas), but it never was a science. There may be lots of people who are Freudian or Adlerian cases: Freud himself was clearly a Freudian case, and Adler an Adlerian case. But what prevents their theories from being scientific in the sense here described is, very simply, that they do not exclude any physically possible human behaviour. Whatever anybody may do is, in principle, explicable in Freudian or Adlerian terms. (Adler's break with Freud was more Adlerian than Freudian, but Freud never looked on it as a refutation of his theory.)

 

The point is very clear. Neither Freud nor Adler excludes any particular person's acting in any particular way, whatever the outward circumstances. Whether a man sacrificed his life to rescue a drowning, child (a case of sublimation) or whether he murdered the child by drowning him (a case of repression) could not possibly be predicted or excluded by Freud's theory; the theory was compatible with everything that could happen—even without any special immunization treatment.

 

Thus while Marxism became non-scientific by its adoption of an immunizing strategy, psychoanalysis was immune to start with, and remained so. In contrast, most physical theories are pretty free of immunizing tactics and highly falsifiable to start with. As a rule, they exclude an infinity of conceivable possibilities.  

 

 

“We must not look upon science as a body of ‘knowledge’, but rather as a system of hypotheses, that I say, as a system of guesses or anticipations which in principle cannot be justified, but with which we work as long as they stand up to tests, and of which we are never justified in saying that we know that they are ‘true’, or ‘more or less certain’ or even ‘probable.’  

 

Contra Induction

 

Popper objected to inductivist views (according to which a scientific theory had to be supported by observations) for two reasons:

 

He argued that it was too easy to find evidence ‘supporting’ a given theory.  (Here he used examples from Freudian psychology, Marxist theory and other places.)

 

He argued that Hume’s critique of induction showed that we simply could not actually support (i.e. give good evidence for) a general claim using evidence from particular cases.

 

Contra Induction

 

Modus Tollens and Modus Moron J

 

If T then O

Not O

Therefore

Not T.

 

Vs.

 

1’.                 If T then O

2’.                 O

Therefore

3’. T.

 

The second of course is an invalid Inference: (The polite, official label for the second argument form is ‘affirming the consequent’…)

 

Popper’s influence on scientists’ own views of their work has been considerable– perhaps even greater than T.S. Kuhn’s influence. 

 

His presentation of science as grounded in the ongoing testing of our theories and always open to the possibility that they will be refuted at the next test, resonates strongly with them.

 

Philosophically, his rejection of induction allowed him to avoid the difficulties the logical empiricists struggled with in their attempts to understand confirmation.

 

But the rejection of induction also leaves a major gap in his understanding of science– we don’t simply regard science as a kind of intellectual game:  we use the results of science to guide our practice when we are engaged in pursuing our ends. 

 

So without some account of induction, Popper’s position provides no account of how or why we should prefer to act in ways our present well-tested but still-standing theories imply will be successful. 

 

Difficulties

 

Popper was know for being extremely persistent and stubborn– as well as very demanding of the students who worked with him.  Nevertheless, his thought certainly did evolve on these issues– but he never budged on any of his fundamental views, including especially the complete rejection of induction.

 

He did attempt to capture some sense of progress for science in terms of accounts of the truth-content and question-content of theories, but these notions were always untenable, and did nothing to resolve the lack of any commitment to induction. 

 

He did some influential work on probability theory, in which conditional probabilities (rather than absolute probabilities) were taken as primitive.

 

A (nother) puzzle about induction

 

There is something odd about Hume’s (and Popper’s) critique of induction and its relation to the modest attitudes of scientists towards even their most successful theories.

 

On one hand, it is clear that (for example) despite its many brilliant successes, Newtonian physics has turned out to be false.

 

The history science is the history of such failures.  This might lead us to think that scientists should doubt that their present theories are true as well. 

 

But their modesty is not a form of Humean skepticism.  Quite the opposite; the modesty arises and is justified by induction.  If we were wrong despite failing to falsify a theory in the past, they we may be wrong in the present and future. 

 

In these cases, the theory fits a large collection of well-established facts,  When this is the case, we don’t expect (nor has it been the case that) similar observations of similar cases undermine the theory later on.

 

The observations scientists are ‘afraid of’ i.e. the ones they suspect may lead to trouble for their presently held theories, are observations of new kinds of facts:  observations of events at higher energies, or on smaller scales, or of new phenomena. 

 

But a true Humean has no more reason to expect new phenomena to give trouble than she has to expect entirely familiar sorts of cases to give trouble. 

 

In either case, it’s only induction that supports our present theory, and Hume and Popper both reject induction as invalid (though Hume thought that it was also indispensable).

 

Further considerations

 

On the other hand, it may well be induction that leads us to suspect theories are more likely to go wrong when we apply them to new kinds of phenomena, or new extremes of parameter values. 

 

Still, pure inductive skepticism like Popper’s draws no line here– induction is invalid, period—not ‘OK’ when applied to familiar cases and dubious when extended beyond them.

 

Fallibilism

 

Fallibilism: The position of accepting (some) of our theories are true, while at the same time, accepting that any or all of them may well turn out to be wrong.

 

 

In fact, scientists can sometimes even predict, based on their theory, the sorts of circumstances in which it’s likely to fail (cf. recent reviews of the LHC and its likely results for the ‘standard model’ in particle physics).

 

But fallibilism does not imply that we have no grounds for accepting our present theories– it only implies that we suspect they may not turn out to be completely true. 

 

Truth as Correspondence

 

There is something odd about thinking in terms of truth here, as well.

 

The methods of science (as Popper rightly saw) continually expose theories to further tests– even a theory that is perfectly reliable in the range of applications we’ve already tried can turn out to be false because it fails in some new application. 

 

Perhaps, given the actual record of science, it would be wiser to say that the goal of science is to achieve greater and greater reliability and precision in our descriptions and explanations.

 

Truth as Correspondence

 

In some sense this actually brings us back to the idea of truth, but in a more reserved way: 

 

Perfect reliability and precision is both something we don’t ever expect to actually achieve, and extremely close to what we would expect (even demand) from a theory we would regard as true.

 

Of course we would also expect maximal power (i.e. we would favor a theory that would constrain our observations more tightly, assuming equal precision and reliability) before we would be tempted to speak of ‘truth, the whole truth, and…

 

Truth as something else? Searching for Truth in all the wrong places….

 

Popper’s skepticism about induction leaves us with little grounds for confidence about making progress in science—

 

Assuming everything works without a hitch as we falsify theories, we may be right in rejecting one theory after another

 

But…

 

We’re left with no sense of progress towards the truth (no reason to suspect that our theories are anything more than falsehoods not yet exposed).

 

Conjecture and Refutation

 

The pattern of scientific work on this account is very simple and repetitive:

 

A scientific conjecture is made.

Scientists try to refute it.

The second step is repeated until it succeeds.

 

While Popper acknowledges that we can respond to a failed test by modifying our theory, or even by modifying some assumptions that were made about the test, he is uncomfortable with this sort of defensive strategy– to Popper this looks ad hoc.

 

Theory construction by means of empirical guidance doesn’t take the sort of risk that Popper thinks a good theory should. 

 

Popper, Falsification and Scientific Demarcation

Conjecture and Refutation

 

The pattern of scientific work on this account is very simple and repetitive:

 

A scientific conjecture is made.

Scientists try to refute it.

The second step is repeated until it succeeds.

 

While Popper acknowledges that we can respond to a failed test by modifying our theory, or even by modifying some assumptions that were made about the test, he is uncomfortable with this sort of defensive strategy– to Popper this looks ad hoc.

 

While Popper acknowledges that we can respond to a failed test by modifying our theory, or even by modifying some assumptions that were made about the test, he is uncomfortable with this sort of defensive strategy– to Popper this looks ad hoc.

 

Theory construction by means of empirical guidance doesn’t take the sort of risk that Popper thinks a good theory should. 

 

Norms and games

 

For Popper these are rules that somehow constitute the game of science.

 

We can do other things (make ad hoc adjustments to our theories or auxiliary hypotheses as new evidence accumulates) but that is playing another game.

 

The surviving theories, at any given time, are no more likely to be right than any other theory not yet refuted by the evidence we have.

 

We have no reason even to suppose that the most basic, reliable phenomena should continue to respect the regularities we have observed in them (this is Hume’s skepticism about induction, which Popper endorses).

 

But scientists are very confident about their ability to reliably produce certain phenomena and the success of their current theories at explaining them–even if they are fallibilists about those theories when applied to new phenomena and observations.

 

Our division of phenomena into kinds is largely a practical matter- the use of certain kinds of apparatus, making certain kinds of measurements, etc. 

 

Competition and selection

 

It’s tempting to draw an analogy between what Popper describes and evolution.

 

Falsification of a theory would be something like extinction.

 

The scientific community continuing to work on an unfalsified theory would be like the continuation of a species over time.

 

But note this is perhaps a telling metaphor.  Evolution does not proceed to ultimate perfection, just suitability to problem sets.

 

Further, survival s secured so long as the entity can adapt.  Evolution is (as Darwin defined it) descent with modification. 

 

On a similar view of scientific “progress,” nothing rules out repeatedly modifying a theory to make it fit the phenomena.

 

Extinction can still occur, if no suitable modifications arise, but it might be forestalled indefinitely by a creative mind.

 

In science, modifications that are purely ad hoc rarely succeed over the longer term. 

 

Further, in evolution many species that are not optimally adapted to their environment can still persist for some time. 

 

In particular, in the absence of superior competition work may well continue on a theory even after scientists are convinced that it is wrong– after all, the work may well focus further investigation on issues that will help with the development of a new theory.

 

From logic to psychology

 

For Popper, as for the positivists, the aim of philosophy of science was to lay out how science should be done, and the criteria for this notion would be fundamentally logical– they would turn on the logical relations between a scientific theory and observations.

 

But the Duhem/Quine problem led him to turn this logical line into a psychological one:  the scientist is someone who should not avoid falsification by blaming ‘auxiliaries’– she would should place her theory in the harshest environment possible, and blame her theory if the results don’t fit.  Here the psychology of decision making replaces the logic of theory and evidence…

 

This means that scientist actually risks rejecting a true theory (if she retains a false auxiliary or even a false observations and consequently regards the theory as falsified). 

 

The last shred of logical progress (a steady accumulation of falsified theories) in Popper’s game of science is lost here.

 

Further, the demarcation Popper had sought becomes problematic too.

 

Popper can still draw a logical line, if he can specify which theories would be falsified by some possible observations– but the users of these theories could still defend them, in principle, by shifting the blame elsewhere.

 

Godfrey-Smith also emphasizes a problem for probabalistic theories (such as classical thermodynamics)– if all they tell us is that certain observations are very  improbable, then strictly speaking they aren’t really falsifiable!  Again, the psychology rather than the logic of science becomes central here.

 

The problem of induction comes home to roost

Godfrey Smith suggests a question Popper cannot credibly answer:

 

Suppose we are building a bridge, and we have two theories we might employ to guide our work.

 

One theory has been tested in many cases, and passed all the tests.

Another has yet to be tested, but (trivially) has passed every test we’ve ever put it to. (i.e. zero)

 

Which should we use?  Both are, to date, unfalsified.

 

But…in Popper’s defense,

 

There is something odd about this example, though: such a new theory, to be relevant, has to cover a lot of the same ground as the old successful theory in terms of explanatory power, etc. – and in order not to be falsified, it must succeed on those tests.

 

 (But there may be a worse example in the wings for Popper.)

 

Upshot of Godfrey Smith’s question:

 

If we discount inductive success thus far entirely, we have no reason to suppose the (“confirmed”) theory will succeed in a further application.

 

But also, without induction, failure in some cases in the past gives us no reason to suppose the theory will fail in a further application.

(Such a theory could not be true, but it could still be a reliable guide to future results!)

 

If we discount inductive success thus far entirely, we have no reason to suppose the (“confirmed”) theory will succeed in a further application.

 

Of course if we can specify a finite range of theories within which we can show the truth must lie, then we can proceed by elimination in a quasi-Popperian way.

Taking risks

 

Even with all these reservations, Godfrey-Smith thinks Popper was onto something worthwhile:

 

The idea that scientific theories must take risks– they must have enough ‘empirical content’ (even as qualified by Duhem and Quine) that they really could be shown (or at least justifiably accepted to have been shown) false. 

 

But this focuses more attention on how a theory is deployed (pragmatic consequences), and how its users respond to difficulties, than on the ‘logic’ of the theory itself. 

 

We can proceed scientifically, if we treat the theory as subject to empirical correction and even refutation.

 

Or we can proceed non-scientifically, by isolating and sheltering the theory from any and all empirical threats.

 

These choices are even open to Freudians and Marxists.

 

What could falsify the Theory of Evolution?: Precambrian Rabbits

 

A standard one-line answer to the question, what would refute evolution.

 

"Precambrian rabbits" or "fossil rabbits in the Precambrian" are reported to have been among responses given by the biologist J.B.S. Haldane when asked what evidence could destroy his confidence in the theory of evolution and the field of study. The answers became popular imagery in debates about evolution and the scientific field of evolutionary biology in the 1990s. 

 

Some accounts use this response to rebut claims that the theory of evolution is not falsifiable by any empirical evidence.

 

This was offered as a justification for regarding evolution as a scientific theory in light of Popper’s insistence that falsifiability is an essential feature of a scientific theory.

 

Popper himself had expressed doubts about the scientific status of evolutionary theory, although he later concluded that the field of study was genuinely scientific.

 

Rabbits are mammals. From the perspective of the philosophy of science, it is doubtful whether the genuine discovery of mammalian fossils in Precambrian rocks would overthrow the theory of evolution instantly, although, if authentic, such a discovery would indicate serious errors in modern understanding about the evolutionary process.

 

Mammals are a class of animals, whose emergence in the geologic timescale is dated to much later than any found in Precambrian strata. Geological records indicate that although the first true mammals appeared in the Triassic period, modern mammalian orders appeared in the Palaeocene and Eocene epochs of the Palaeogene period. Hundreds of millions of years separate this period from the Precambrian

 

 

Of course it would take very careful work to establish such an astounding result. 

 

But there are many other tests evolution has passed and continues to pass (the in-principle independent tree-structures of taxonomy, biochemistry, development and the fossil record continue to match up, for example).

 

Applying new tests to these trees has led to many new results and much refinement of our views on the course of evolution—but they have always fit within the narrow range of results acceptable for evolution.  

 

Objection: Falsificationism is ‘No criterion of truth’:

 

There is no Theory/Observation distinction:

 

If this is true, then accepting an observation statement will require accepting the theory in which the observation statement occurs.

 

But if this is true, then is it unclear if or how we could really falsify a theory via observation, at least in a truly revolutionary way.

Popper, Falsification and Scientific Demarcation

 

All observations are selective and theory laden

 

‘Here is a glass of water’ is theory laden

 

In accepting the statement we must accept a significant amount of theory.

 

We have only as much justification for accepting the observation statement as we do for the theory of which is it a part and which makes it possible.

 

Upshot: we cannot use observation to establish the truth of a theory

 

So how can we establish the truth of scientific theories? 

We Kan’t! 

 



[1] http://www.esa.int/Our_Activities/Space_Science/Relativity_and_the_1919_eclipse

 

[2] Which of course raises the question, what precisely is a “basic” statement.  Recall that Quine et al. says there aint no such thing.