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Looking for a Black Swan


Karl Popper, who died in 1994, was one of the most influential philosophers of the twentieth century—as much outside the profession of philosophy as within it (Chancellor Helmut Schmidt, Sir Peter Medawar, and Sir Ernst Gombrich were ardent Popperians). An emigrant from Vienna in 1937, who had fled the Nazis, Popper spent his early academic years in New Zealand before obtaining a post at the London School of Economics in 1945, where he taught until he re-tired. (Popper’s early years are comprehensively covered in Malachi Haim Hacohen’s The Formative Years.) Polymathic, prolific, strong-willed, he made his mark in both the philosophy of science and political philosophy, later developing distinctive views in the philosophy of mind and even Greek philosophy.

His initial philosophical impetus came from the Vienna Circle, a group of scientifically inclined philosophers and scientists who flourished in the interwar years and who espoused the philosophy that came to be known as “logical positivism”—a view best defined as against religion and traditional metaphysics and for empir-ical science (A.J. Ayer’s Language, Truth and Logic introduced this philosophy to the English-speaking world in 1946). However, Popper said that he diverged profoundly from the Vienna Circle, particularly over the nature of scientific method: while they took empirical verifiability as the touchstone of science (and hence intellectual respectability), Popper took the notion of falsification as the essential mark of scientific discourse. This key idea was to have a large impact on the philosophy of science, as well as on the whole issue of what constituted reputable discourse. The recent books devoted to Popper attest to the vitality of the ideas he introduced.1 While not being a guru within the narrow confines of analytical philosophy, when compared, say, to Wittgenstein, he continues to be a major intellectual figure in the world beyond.

There is an impressive and attractive unity to Popper’s thought. In his philosophy of science, his general theory of knowledge, his philosophy of biology, and his political philosophy the same basic ideas recur. For Popper, everything revolves around the solving of problems by means of the critical elimination of attempted solutions. In “The Logic and Evolution of Scientific Theory,” the first essay in the aptly named All Life Is Problem Solving, a collection of his later lectures and essays, Popper offers us a three-stage model of learning, which he takes to apply to animal learning as well as to the upper reaches of scientific research: first there is the problem (Popper is very fond of the emphatic use of italics); then there are the attempted solutions; finally there is the elimination of those solutions. Epistemic progress works by trial and error.

In the case of scientific knowledge this three-stage model assumes the familiar Popperian form: the scientist is confronted by a problem in accepted theory, occasioned by a faulty prediction or explanatory weakness, which leads to the need for a new theory; she generates, by means of imaginative creativity, a range of conjectures or guesses as to what might be a preferable theory; she then sets about trying to falsify these conjectures, until only one is left standing. In this way objective scientific knowledge grows.

According to Popper it is not that scientists work by observing the world, performing inductive inferences, and confirming hypotheses, which then get added to the stock of permanent truths. Science does not begin with observation at all, but with problems. Theories are not derived from data by some inference such as induction (if you observe a number of white swans you are entitled to infer that all swans are white), but rather are the free products of human creativity; and scientists do not confirm or verify hypotheses, but refute them. Scientific knowledge is essentially negative: what we know is that certain conjectures are not true—those that have been falsified; we never have any positive reason to believe a hypothesis, since confirmation is not what science is about.

Induction, for Popper, is simply logically invalid, since you cannot infer that all swans are white merely from having observed that all the ones you have come across are; and anyway induction is not actually used by scientists. The best we can say of a theory is that it has not (yet) been refuted. Thus there is no room for dogmatism in science; modesty is the only sensible attitude. Science consists of conjectures that have not been rejected, not of accepted facts derived from observation of the world.

Popper suggests that this three-stage process has its counterpart in the behavior of organisms:

At bottom, this procedure [the falsifying of attempted solutions to problems] seems to be the only logical one. It is also the procedure that a lower organism, even a single-cell amoeba, uses when trying to solve a problem. In this case we speak of testing movements through which the organism tries to rid itself of a troublesome problem. Higher organisms are able to learn through trial and error how a certain problem should be solved. We may say that they too make testing movements—mental testings—and that to learn is essentially to try out one testing movement after another until one is found that solves the problem. We might compare the animal’s successful solution to an expectation and hence to a hypothesis or a theory.

The difference between the amoeba and Einstein, Popper says, is that the latter organism uses the critical method: arguments are expressed in language and subjected to self-consciously critical scrutiny. Thus science is a rational enterprise, engaging an objective world of reasons, argument, and truth (what Popper calls “World 3”). But in basic structure the scientist is as much a trial-and-error learner as the amoeba; the three-stage model is a biological universal. Moreover, Popper argues, this model applies also to Darwin’s theory of evolution. The species encounters a problem of adaptation as a result of a change in the environment; it needs to evolve genetically or become extinct. Mutations spontaneously occur, which in Popper’s view function as possible solutions; most are fatal to the organism in question, which is then eliminated. But a mutation may prove resistant to elimination, and hence come to characterize the species—until a new problem of adaptation comes along. A mutation is like a new conjecture that invites refutation; natural selection consists in the elimination of bad conjectures. Biological evolution is just more conjecture and refutation, bold stabs in the dark followed by summary ejection. But this seemingly negative process produces magnificent results—just as it does in science.

Even in politics Popper applies the same template. The “open society” is one that invites and encourages critical discussion: there are no inviolable ideologies, like Marxism, only a plurality of perspectives, each subject to critical evaluation. The essence of democracy is not “rule of the people” whereby government decisions reflect the collective will, but rather the possibility of (peacefully) removing a government that does not stand up to critical appraisal—as it were, falsifying the policies pursued by the government. Hitler and Stalin were, among other things, dogmatic ideologues in the grip of theories they made no effort to falsify, and they produced governments in which criticism and peaceful replacement of a government were not tolerated.2

The open society is like a scientific conference in which everyone is critical of his own current conjectures, and helpfully critical of others, and in which authority can be transferred according to general consent. Peace and happiness result from a willingness to admit error, from an accepted fallibility. The Cartesian ideal of secure foundations, unquestionable certainty, is not only a philosopher’s mistake; it is, for Popper, the root of the dogmatism that produced the worst excesses of the twentieth century. We should not be trying to arrive at beliefs that can be guaranteed to be true, but rather freely creating conjectures that we are keen to see refuted. Detecting error is the primary virtue, not proving truth.

There is in the sweep of these ideas a large vision, both romantic and hardheaded, that can be captivating: the scientist as a bold adventurer, living out his biological destiny, bringing his open-mindedness and free creativity to a confused and oppressed world—who can fail to be touched by such an image? These ideas produce an exhilaration akin to that produced by the Vienna Circle, with whom Popper had a troubled relationship. The members of the Vienna Circle, too, were politically liberal and impressed with science as a model of all that is good and noble. They were also much concerned with the nature of scientific method. Once scientific method was properly understood, and this method applied across the board, we should, they thought, be able to liberate ourselves from pseudo-science, dogmatic religion, and political ideology, thus opening the way to a free and open society.

This ideal—science as the model of civilization and genuine knowledge—Popper fully shared, but he also took himself to have demolished logical positivism. There are two main reasons for this. First, he thought he had shown that science does not proceed by verifying hypotheses, as by observing a number of white swans and concluding that the hypothesis that all swans are white is true; indeed, he thought he had shown that there is no such valid form of reasoning—since induction is logically indefensible (you can’t derive an “all” from a “some”). Rather, science proceeds by falsification, which is logically impeccable, since the observation of a single black swan decisively refutes the hypothesis that all swans are white.

Secondly, the positivists took empirical verifiability, the apparent confirmation of a hypothesis by experiment and observation, to mark the boundary between sense and nonsense, so that traditional metaphysical questions such as whether God exists or time is real are strictly meaningless—a result they enthusiastically welcomed. Popper, by contrast, took his falsifiability criterion as marking the line between what was science and what was not—with no imputation that the empirically unfalsifiable lacked all sense. Therefore metaphysical issues—such as the question of whether the mind is separate from the body or whether numbers are independent of the mind—are meaningful and pursuing them was a potentially worthwhile enterprise. Psychoanalysis for Popper was also meaningful, but he declared it a pseudoscience because he did not believe its propositions could be subjected to falsification.

Popper’s divergences from the Vienna Circle should not be exaggerated, however, despite his frequent protestations that he was not at all a positivist. He is still proposing as a mark of science a criterion that stresses empirical testability—but for him the tests aim at the empirical rejection of theories instead of showing their empirical acceptability. And the difference in their views of the status of what lies outside science is not in practice as great as it might appear: for Popper, too, took his criterion as having a normative dimension—to wit, that what failed it was less respectable than real science. Hence his assault on Marxian and Freudian theory as pseudosciences—bodies of thought that should not be taken seriously. Popper’s entire outlook falls squarely within the general frame laid down by the Vienna Circle.

  1. 1

    Routledge has also recently reissued, in attractive paperback form, most of Popper’s main works: The Logic of Scientific Discovery, Conjectures and Refutations, and The Poverty of Historicism.

  2. 2

    Karl Popper: Lesson of This Century contains a series of essays about twentieth-century politics that blends historical judgment with general principles, thus applying the ideas of The Open Society and Its Enemies.

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