[1963]
KARL POPPER (1902-1994) was one of the twentieth century's most well-known and important philosophers of science. He was born in Vienna in 1902 to a German- Jewish family that had converted to the Lutheran Church before he was born. In 1918, at the age of sixteen, he entered the University of Vienna and studied mathematics, physics, and psychology with the intention of becoming an elementary or secondary school teacher. In 1928, he received a Ph.D. in psychology and began teaching mathematics and physics to secondary students in Austria. While teaching, he wrote his first book, The Logic of Scientific Discovery (1934).
In 1936, Popper left Austria for England, fearing the rise of Nazism and increased persecution of Jews. A year later, he accepted an academic position in New Zealand, where he stayed for ten years. In 1946, he returned to England and accepted a position teaching philosophy at the prestigious London School of Economics. He continued to publish books in both political philosophy and the philosophy of science, earning a reputation as one of the most important philosophers of the twentieth century. In 1965, he was knighted by Queen Elizabeth II, and in 1976, he was elected a fellow of the Royal Society of England.
Popper's most important contribution to science was his redefinition of the scientific method. Since the beginning of the Scientific Revolution in the sixteenth century, science had been understood as a method for testing and proving various theories and hypotheses. Popper felt that this concept of the scientific method made it very easy for nonscientific and pseudoscientific theories like palm reading and astrology to claim scientific status. Since it is always possible to read events and results as confirmations of a theory, he reasoned, the prevailing scientific model gave no way of distinguishing between science and folklore.
Popper ultimately concluded that a genuine scientific theory must make predictions that can be tested by other scientists, who must try to prove the theory false. Theories that cannot be disproved can be considered conditionally true until such time as they are falsified. In the essay presented below, which is based on a lecture that he first delivered as part of a course on contemporary British philosophy at Cambridge in 1953, Popper offers his clearest explanation of the nature of science as a process of falsification.
Science: Conjectures and Refutations
Mr. Turnbull had predicted evil consequences, . . . and was now doing the best in his power to bring about the verification of his own prophecies.
Anthony Trollope
I
When I received the list of participants in this course and realized that I had been asked to speak to philosophical colleagues I thought, after some hesitation and consultation, that you would probably prefer me to speak about those problems which interest me most, and about those developments with which I am most intimately acquainted. I therefore decided to do what I have never done before: to give you a report on my own work in the philosophy of science, since the autumn of 1919 when I first began to grapple with the problem, 'When should a theory be ranked as scientific?' or 'Is there a criterion for the scientific character or status of a theory V
The problem which troubled me at the time was neither, 'When is a theory true?' nor, 'When is a theory acceptable?' My problem was different. I wished to distinguish between science and pseudo-science; knowing very well that science often errs, and that pseudo-science may happen to stumble on the truth.
I knew, of course, the most widely accepted answer to my problem: that science is distinguished from pseudo-science—or from 'metaphysics'—by its empirical method, which is essentially inductive, proceeding from observation or experiment. But this did not satisfy me. On the contrary, I often formulated my problem as one of distinguishing between a genuinely empirical method and a non-empirical or even a pseudo-empirical method—that is to say, a method which, although it appeals to observation and experiment, nevertheless does not come up to scientific standards. The latter method may be exemplified by astrology, with its stupendous mass of empirical evidence based on observation—on horoscopes and on biographies.
But as it was not the example of astrology which led me to my problem I should perhaps briefly describe the atmosphere in which my problem arose and the examples by which it was stimulated. After the collapse of the Austrian Empire[159] there had been a revolution in Austria: the air was full of revolutionary slogans and ideas, and new and often wild theories. Among the theories which interested me Einstein's theory of relativity was no doubt by far the most important. Three others were Marx's theory of history, Freud's psycho-analysis, and Alfred Adler's2 so-called 'individual psychology'.
2. Alfred Adler: Austrian psychologist (18701937) with whom Popper studied at the University of Vienna.
There was a lot of popular nonsense talked about these theories, and especially 5 about relativity (as still happens even today), but I was fortunate in those who introduced me to the study of this theory. We all—the small circle of students to which I belonged—were thrilled with the result of Eddington's[160] eclipse observations which in 1919 brought the first important confirmation of Einstein's theory of gravitation. It was a great experience for us, and one which had a lasting influence on my intellectual development.
The three other theories I have mentioned were also widely discussed among students at that time. I myself happened to come into personal contact with Alfred Adler, and even to co-operate with him in his social work among the children and young people in the working-class districts of Vienna where he had established social guidance clinics.
It was during the summer of 1919 that I began to feel more and more dissatisfied with these three theories—the Marxist theory of history, psychoanalysis, and individual psychology; and I began to feel dubious about their claims to scientific status. My problem perhaps first took the simple form, 'What is wrong with Marxism, psycho-analysis, and individual psychology? Why are they so different from physical theories, from Newton's theory, and especially from the theory of relativity?'
To make this contrast clear I should explain that few of us at the time would have said that we believed in the truth of Einstein's theory of gravitation. This shows that it was not my doubting the truth of those other three theories which bothered me, but something else. Yet neither was it that I merely felt mathematical physics to be more exact than the sociological or psychological type of theory. Thus what worried me was neither the problem of truth, at that stage at least, nor the problem of exactness or measurability. It was rather that I felt that these other three theories, though posing as sciences, had in fact more in common with primitive myths than with science; that they resembled astrology rather than astronomy.
I found that those of my friends who were admirers of Marx, Freud, and Adler, were impressed by a number of points common to these theories, and especially by their apparent explanatory power. These theories appeared to be able to explain practically everything that happened within the fields to which they referred. The study of any of them seemed to have the effect of an intellectual conversion or revelation, opening your eyes to a new truth hidden from those not yet initiated. Once your eyes were thus opened you saw confirming instances everywhere: the world was full of verifications of the theory. Whatever happened always confirmed it. Thus its truth appeared manifest; and unbelievers were clearly people who did not want to see the manifest truth; who refused to see it, either because it was against their class interest, or because of their repressions which were still 'un-analysed' and crying out for treatment.