Theory and Reality

by Peter Godfrey-Smith

  4.1 Popper's Unique Place in the Philosophy of Science

  Karl Popper is the only philosopher discussed in this book who is regarded as a hero by many scientists. Attitudes toward philosophy among scientists vary, but hardly ever does a philosopher succeed in inspiring scientists in the way Popper has. It is also rare for a philosopher's view of science to be used within a scientific debate to justify one position over another. This has happened with Popper too. Within biology, recent debates about the classification of organisms and about ecology have both seen Popper's ideas used in this way (Hull 1999). I once went to a lecture by a famous virologist who had won a Nobel Prize in medicine, to hear about his work. What I heard was mostly a lecture about Popper. In 1965, Karl Popper even became Sir Karl Popper, knighted by the queen of England.

  Popper's appeal is not surprising. His view of science is centered around a couple of simple, clear, and striking ideas. His vision of the scientific enterprise is a noble and heroic one. Popper's theory of science has been criticized a great deal by philosophers over the years. I agree with many of these criticisms and don't see any way for Popper to escape their force. Despite the criticism, Popper's views continue to have an important place in philosophy and continue to appeal to many working scientists.

  4.2 Popper's Theory of Science

  Popper began his intellectual career in Vienna, between the two world wars. He was not part of the Vienna Circle, but he did have contact with the logical positivists. This contact included a lot of disagreement, as Popper developed his own distinctive position. Popper does count as an "empiricist" in the broad sense used in this book, but he spent a lot of time distinguishing his views from more familiar versions of empiricism. Like the logical positivists, Popper left Europe upon the rise of Nazism, and after spending the war years in New Zealand, he moved to the London School of Economics, where he remained for the rest of his career. There he built up a loyal group of allies, whom he often accused of disloyalty. His seminar series at the London School of Economics became famous for its grueling questioning and for the fact that speakers had a difficult time actually presenting much of their lectures, because of Popper's interruptions.

  Popper once had a famous confrontation with Wittgenstein, on the Tat-ter's turf at Cambridge University. One version of the story, told by Popper himself, has Wittgenstein brandishing a fireplace poker during a discussion of ethical rules, leading Popper to give as an example of an ethical rule: "not to threaten visiting lecturers with pokers." Wittgenstein stormed out. Other versions of the story, including those told by Wittgenstein's allies, deny Popper's account (see Edmonds and Eidinow zoos for this controversy).

  The logical positivists developed their theory of science as part of a general theory of language, meaning, and knowledge. Popper was not much interested in these broader topics, at least initially; his primary aim was to understand science. As his first order of business, he wanted to understand the difference between scientific theories and nonscientific theories. In particular, he wanted to distinguish science from "pseudo-science." Unlike the logical positivists, he did not regard pseudo-scientific ideas as meaningless; they just weren't science. For Popper, an inspiring example of genuine science was the work of Einstein. Examples of pseudo-science were Freudian psychology and Marxist views about society and history.

  Popper called the problem of distinguishing science from nonscience the "problem of demarcation." All of Popper's philosophy starts from his proposed solution to this problem. "Falsificationism" was the name Popper gave to his solution. Falsificationism claims that a hypothesis is scientific if and only if it has the potential to be refuted by some possible observation. To be scientific, a hypothesis has to take a risk, has to "stick its neck out." If a theory takes no risks at all, because it is compatible with every possible observation, then it is not scientific. As I said above, Popper held that Marx's and Freud's theories were not scientific in this sense. No matter what happens, Popper thought, a Marxist or a Freudian can fit it somehow into his theory. So these theories are never exposed to any risks.

  So far I have described Popper's use of falsifiability to distinguish scientific from nonscientific theories. Popper also made use of the idea of falsification in a more far-reaching way. He claimed that all testing in science has the form of attempting to refute theories by means of observation. And crucially, for Popper it is never possible to confirm or establish a theory by showing its agreement with observations. Confirmation is a myth. The only thing an observational test can do is to show that a theory is false. So the truth of a scientific theory can never be supported by observational evidence, not even a little bit, and not even if the theory makes a huge number of predictions that all come out as expected.

  As you might think, Popper was a severe critic of the logical empiricists' attempts to develop a theory of confirmation or "inductive logic." The problems they encountered, some of which I discussed in chapter 3, were music to his ears. Popper, like Hume, was an inductive skeptic, and Popper was skeptical about all forms of confirmation and support other than deductive logic itself.

  Skepticism about induction and confirmation is a much more controversial position than Popper's use of falsification to solve the demarcation problem. Most philosophers of science have thought that if induction and confirmation are just myths, that is very bad news for science. Popper tried to argue that there is no reason to worry; induction is a myth, but science does not need it anyway. So inductive skepticism, for Popper, is no threat to the rationality of science. In the opinion of most philosophers, Popper's attempt to defend this radical claim was not successful, and some of his discussions of this topic are rather misleading to readers. As a result, some of the scientists who regard Popper as a hero do not realize that Popper believed it is never possible to confirm a theory, not even slightly, and no matter how many observations the theory predicts successfully.

  Popper placed great emphasis on the idea that we can never be completely sure that a theory is true. After all, Newton's physics was viewed as the best-supported theory ever, but early in the twentieth century it was shown to be false in several respects. However, almost all philosophers of science accept that we can never be zoo percent certain about factual matters, especially those discussed in science. This position, that we can never be completely certain about factual issues, is often known as fallibilism (a term due to C. S. Peirce). Most philosophers of science accept fallibilism. The harder question is whether or not we can be reasonable in increasing our confidence in the truth of a theory when it passes observational tests. Popper said no. The logical empiricists and most other philosophers of science say yes.

  So Popper had a fairly simple view of how testing in science proceeds. We take a theory that someone has proposed, and we deduce an observational prediction from it. We then check to see if the prediction comes out as the theory says it will. If the prediction fails, then we have refuted, or falsified, the theory. If the prediction does come out as predicted, then all we should say is that we have not yet falsified the theory. For Popper, we cannot conclude that the theory is true, or that it is probably true, or even that it is more likely to be true than it was before the test. The theory might be true, but we can't say more than that.

  We then try to falsify the theory in some other way, with a new prediction. We keep doing this until we have succeeded in falsifying it. What if years pass and we seem to never be able to falsify a theory, despite repeated tests? We can say that the theory has now survived repeated attempts to falsify it, but that's all. We never increase our confidence in the truth of the theory; and ideally, we should never stop trying to falsify it. That's not to say we should spend all our time testing theories that have passed tests over and over again. We do not have the time and resources to test everything that could be tested. But that is just a practical constraint. According to Popper, we should always retain a tentative attitude toward our theories, no matter how successful they have been in the past.

  In
defending this view, Popper placed great emphasis on the difference between confirming and disconfirming statements of scientific law. If someone proposes a law of the form "All F's are G," all it takes is one observation of an F that is not a G to falsify the hypothesis. This is a matter of deductive logic. But it is never possible to assemble enough observations to conclusively demonstrate the truth of such a hypothesis. You might wonder about situations where there is only a small number of F's and we could hope to check them all. Popper and the logical empiricists regarded these as unimportant situations that do not often arise in science. Their aim was to describe testing in situations where there is a huge or infinite number of cases covered by a hypothesized law or generalization. So Popper stressed that universal statements are hard or impossible to verify but easy, in principle, to falsify. The logical empiricist might reply that statements of the form "Some F's are G" have the opposite feature; they are easy to verify but hard or impossible to falsify. But Popper claimed (and the logical empiricists tended to agree) that real scientific theories rarely take this form, even though some statements in science do.

  Despite insisting that we can never support or confirm scientific theories, Popper believed that science is a search for true descriptions of the world. How can one search for truth if confirmation is impossible?

  This is an unusual kind of search. We might compare it to a certain kind of search for the Holy Grail, conducted by an imaginary medieval knight. Suppose there are lots of grails around, but only one of them is holy. In fact, the number of nonholy grails is infinite or enormous, and you will never encounter them all in a lifetime. All the grails glow, but only the Holy Grail glows forever. The others eventually stop glowing, but there is no telling when any particular nonholy grail will stop glowing. All you can do is pick up one grail and carry it around and see if it keeps on glowing. You are only able to carry one at a time. If the one you are carrying is the Holy Grail, it will never stop glowing. But you would never know if you currently had the Holy Grail, because the grail you are carrying might stop glowing at any moment. All you can do is reject grails that are clearly not holy (since they stop glowing at some point) and keep picking up a new one. You will eventually die (with no afterlife, in this scenario) without knowing whether you succeeded.

  This is similar to Popper's picture of science's search for truth. All we can do is try out one theory after another. A theory that we have failed to falsify up till now might, in fact, be true. But if so, we will never know this or even have reason to increase our confidence.

  4.3 Popper on Scientific Change

  So far I have described Popper's views about the demarcation of science from nonscience and the nature of scientific testing. Popper also used the idea of falsification to propose a theory of scientific change.

  Popper's theory has an appealing simplicity. Science changes via a twostep cycle that repeats endlessly. Stage i in the cycle is conjecture-a scientist will offer a hypothesis that might describe and explain some part of the world. A good conjecture is a bold one, one that takes a lot of risks by making novel predictions. Stage z in the cycle is attempted refutation-the hypothesis is subjected to critical testing, in an attempt to show that it is false. Once the hypothesis is refuted, we go back to stage i again-a new conjecture is offered. That is followed by stage z, and so on.

  As the process moves along, it is natural for a scientist to propose conjectures that have some relation to previous ones. A theoretical idea can be refined and modified via many rounds of conjecture and refutation. That is fine, for Popper, though it is not essential. One thing that a scientist should not do, however, is to react to the falsification of one conjecture by cooking up a new conjecture that is designed to just avoid the problems revealed by earlier testing, and which goes no further. We should not make ad hoc moves that merely patch the problems found in earlier conjectures. Instead, a scientist should constantly strive to increase the breadth of application of a theory and increase the precision of its predictions. That means constantly trying to increase the "boldness" of conjectures.

  What sort of theory is this? Popper intended it as a description of the general pattern that we actually see in science, and as a description of good scientific behavior as well. He accepted that not all scientists succeed in sticking to this pattern of behavior all the time. Sometimes people become too wedded to their hypotheses; they refuse to give them up when testing tells them to. But Popper thought that a lot of actual scientific behavior does follow this pattern and that we see it especially in great scientists such as Einstein. For Popper, a good or great scientist is someone who combines two features, one corresponding to each stage of the cycle. The first feature is an ability to come up with imaginative, creative, and risky ideas. The second is a hard-headed willingness to subject these imaginative ideas to rigorous critical testing. A good scientist has a creative, almost artistic, streak and a tough-minded, no-nonsense streak. Imagine a hard-headed cowboy out on the range, with a Stradivarius violin in his saddlebags. (Perhaps at this point you can see some of the reasons for Popper's popularity among scientists.)

  Popper's view here can apparently be applied in the same way to individuals and to groups of scientists. An isolated individual can behave scientifically by engaging in the process of conjecture and refutation. And a collection of scientists can each, at an individual level, follow Popper's twostep procedure. But another possibility is a division of labor; one individual (or team) comes up with a conjecture, and another does the attempted refutation. Popper's basic description of the twostep conjecture-andrefutation pattern of science seems compatible with all these possibilities. But the case where individual A does the conjecture and individual B does the refutation will be suspicious to Popper. If individual A is a true scientist, he should take a critical attitude toward his own ideas. If individual A is completely fixated on his conjecture, and individual B is fixated on showing that A is wrong in order to advance his own conjecture, this is not good scientific behavior according to Popper.

  This raises an interesting question. Empiricist philosophies stress the virtues of open-mindedness, and Popper's view is no exception. But perhaps an open-minded community can be built out of a collection of rather closedminded individuals. If actual scientists are wedded to their own conjectures, but each is wedded to a different conjecture and would like to prove the others wrong, shouldn't the overall process of conjecture and refutation work? What is wrong with the situation where B's role is to critically test A's ideas? So long as the testing occurs, what does it matter whether A or B does it? One problem is that if everyone is so closedminded, the results of the test might have no impact on what people believe. Perhaps the young and tender minds of incoming graduate students could be the community's source of flexibility; unsuccessful theories will attract no new recruits and will die with their originators. This would be a rather slow way for science to change (but many would argue that we do see cases like this).

  In later chapters of this book, we will look at theories that focus on social structure in science, and at various kinds of division of labor between individual scientists. Although Popper did stress community standards in science, he did seem to have a picture in which the good scientist should, as an individual, have the willingness to perform both the imaginative and the critical roles. A good scientist should retain a tentative attitude toward all theories, including his own.

  I will make one more point before moving on to criticisms of Popper. The twostep process of conjecture and refutation that Popper describes has a striking resemblance to another twostep process: Darwin's explanation of biological evolution in terms of variation and natural selection. In science according to Popper, scientists toss out conjectures that are subjected to critical testing. In evolution, according to both Darwin himself and more recent versions of evolutionary theory, populations evolve via a process in which variations appear in organisms in a random or "undirected" way, and these novel characteristics are "tested" through thei
r effects on the organism in its interactions with the environment. Variations that help organisms to survive and reproduce, and which are of the kind that gets passed on in reproduction, tend to be preserved and become more common in the population over time.

  Ironically, at one time Popper thought that Darwinism is not a scientific theory, but he later retracted that claim. In any case, both Popper and others have explored the analogy between Popperian science and Darwinian evolution in detail. The analogy should not be taken too seriously; evolution is not a process in which populations really "search" for anything, in the way that scientists search for good theories, and there are other crucial differences too. But the similarity is certainly interesting. Analogies between science and evolution will come again in later chapters (6 and i i).

  4.4 Objections to Popper on Falsification

  Let us now turn to a critical assessment of Popper's ideas. We should start with his solution to the demarcation problem. Is falsifiability a good way to distinguish scientific ideas from nonscientific ones?

  Let me first say that I think this question probably has no answer in the form in which Popper expressed it. We should not expect to be able to go through a list of statements or theories and label them "scientific" or "not scientific." However, I suggest that something fairly similar to Popper's question about demarcation does make sense: can we describe a distinctive scientific strategy of investigating the world, a scientific way of handling ideas?

  Some of Popper's ideas are useful in trying to answer this question. In particular, Popper's claim that scientific theories should take risks is a good one; this will be followed up in the last section of this chapter. But Popper had an overly simple picture of how this risk-taking works.