In this paper I shall venture into an area with which I am not very familiar and in which I feel far from confident; namely into phenomenology. My main motive is not to get away from standard, boring, methodological questions like those of induction and demarcation; but the conviction that a phenomenological account of the empirical basis forms a necessary complement to Popper’s falsificationism. According to the latter, a scientific theory is a synthetic and universal, hence unverifiable proposition. In fact, in order to be technologically useful, a scientific hypothesis must refer to future states-of-affairs; it ought therefore to remain unverified.

The first Darwin Lecture was given in 1977 by Karl Popper. He there said that he had known Darwin’s face and name ‘for as long as I can remember’ (‘NSEM’ p. 339); for his father’s library contained a portrait of Darwin and translations of most of Darwin’s works (‘IA’, p. 6). But it was not until Popper was in his late fifties that Darwin begin to figure importantly in his writings, and he was nearly seventy when he adopted from Donald Campbell the term ‘evolutionary epistemology’ as a name for his theory of the growth of knowledge (OK, p. 67). There were people who saw evolutionary epistemology as a major new turn in Popper’s philosophy.

There is a sort of scepticism, or, at least, epistemological pessimism, that is generated by appealing to Darwin’s theory of evolution. The argument is that nature, that is the selective pressures of evolution, has clearly fitted us for certain sorts of learning and mundane understanding, directly beneficial in point of individual survival and chances for reproduction. Very likely then, it is argued, nature has not fitted us for arcane intellectual accomplishments remote from, or quite disconnected from, those ends. So, it is suggested, perhaps we cannot understand, perhaps never will understand, because we are not made to understand, such matters as consciousness, its nature and causes, the origins of life, the beginning of the universe, or astro-physics in its more finalist pretensions. Sometimes, taken with the claim that manifestly we do understand some of these things, the argument becomes a reductio, and its exponents claim that consequently Darwinism must be false, or of only limited application. More commonly, however, in ‘naturalized epistemology’, it is made the vehicle of a claim about the limits of science, limits imposed by the evolutionarily derived frailty of human understanding.

Popper’s writings cover a remarkably wide range of subjects. The spectrum runs from Plato’s theory of politics to the foundations of quantum mechanics. Yet even amidst this variety the philosophy of probability occupies a prominent place. David Miller once pointed out to me that more than half of Popper’s The Logic of Scientific Discovery is taken up with discussions of probability. I checked this claim using the 1972 6th revised impression of The Logic of Scientific Discovery, and found that of the approximately 450 pages of text, approximately 250 are to do with probability. Thus Miller’s claim is amply justified. It seems indeed that the philosophy of probability was one of Popper’s favourite subjects, and, as we shall see, Popper certainly enriched the field with several striking innovations. In this area, as in others, Popper held very definite views, and criticized his opponents in no uncertain terms. Popper was an objectivist and anti-Bayesian, and his criticisms were directed against subjectivism and Bayesianism.

We all think that science is special. Its products—its technological spin-off—dominate our lives which are thereby sometimes enriched and sometimes impoverished but always affected. Even the most outlandish critics of science such as Feyerabend implicitly recognize its success. Feyerabend told us that science was a con-game. Scientists had so successfully hood-winked us into adopting its ideology that other equally legitimate forms of activity—alchemy, witchcraft and magic—lost out. He conjured up a vision of much enriched lives if only we could free ourselves from the domination of the ‘one true ideology’ of science just as our ancestors freed us from the domination of the Church. But he told us these things in Switzerland and in California happily commuting between them in that most ubiquitous product of science—the aeroplane.

In these prefatory remarks, which are designed to locate my topic within the complex and wide-stretching field of Popper’s thought and writings, I shall not say anything that those familiar with his work will not already know. Moreover, what I do say will take as understood many of the problems and theories, not to mention the terminology, that I shall later be doing my best to make understandable. My apologies are therefore due equally to those who know something about Popper’s discussions of indeterminism and of the propensity interpretation of probability, and to those who know nothing.

There is no doubt at all that the issue of determinism versus indeterminism was a central, dominating theme of Popper’s thought. By his own account he saw his criticism of the thesis of determinism as crucial to his defence not only of the reality of human freedom, moral responsibility and creativity but also as equally fundamental to his account of human rationality and to his theory of the content and growth of science as an objective, rational and most importantly demonstrably rational enterprise. Consequently a great deal of his writings discussing both the content and methodology of the natural and the social sciences alternately bear upon and presuppose his defence of indeterminism.

Karl Popper attempted to give an account of scientific research as the rational pursuit of the truth about nature without any appeal to what he took to be the fictitious notion of non-demonstrative or inductive support. Deductive inference can be seen to be inference enough for science, he claimed, once we appreciate the power of data to refute theory. Many of the standard objections to Popper’s account purport to show that his deductivism actually entails a radical scepticism about the possibility of scientific knowledge. Some of these objections appear unanswerable in the context of the traditional analysis of knowledge as justified true belief; but this is neither a conception of knowledge that Popper himself accepted nor one that is currently in fashion. Reliabilism, the view that knowledge is a true belief generated by a reliable method, is now a popular replacement for the traditional analysis and one that is closer to Popper’s own conception of knowledge. My aim in this essay is to consider in brief compass the prospects of a reliabilist reading of Popper’s account of science. Such a reading makes it possible to turn some of the standard objections and helps to show which of Popper’s views should be accepted and which rejected.

It is one of Karl Popper’s great distinctions that he has an intense—some would say too intense—awareness of the history of philosophy within which he works. He knows not only its patterns, but also its comedies, and sometimes he plays rhetorically against their grain. He knows, for example, that the drive to consistency tends to turn philosophy into compositions of related doctrines, each seeming to involve the others. Religious belief, for example, tends to go with idealism and free will, religious scepticism with materialism and determinism. Popper does not believe in a religion, was for long some kind of a socialist, and takes his bearings from the philosophy of science. Aha! it seems we have located him. Here is a positivist, a materialist, probably a determinist. But of course he denies he is any of these things. Again, like many modern thinkers, he wants to extend scientific method not only to the social sciences but also to history. So far so familiar, until we discover that he regards nature as no less ‘cloudy’ than human societies.

Science, and in particular the process of theory-change in science, formed the major inspiration for Karl Popper’s whole philosophy. Popper learned about the success of Einstein’s revolutionary new theory in 1919 (the same year in which his discontent with Marxism and Freudianism reached crisis-point), and Einstein ‘became a dominant influence on my thinking—in the long run perhaps the most important influence of all.’ Popper explained why.

Karl Popper’s work is of great diversity. It touches on virtually every intellectual activity. But he himself considered his philosophy of science one of his most important achievements. And indeed his achievement here is revolutionary. It destroyed the philosophy of inductivism which held sway over science for hundreds of years.

Popper wrote extensively on the quantum theory. In Logic der Forschung (LSD) he devoted a whole chapter to the topic, while the whole of Volume 3 of the Postscript to the Logic of Scientific Discovery is devoted to the quantum theory. This volume entitled Quantum Theory and the Schism in Physics (QTSP) incorporated a famous earlier essay, ‘Quantum Mechanics without “the Observer”’ (QM). In addition Popper’s development of the propensity interpretation of probability was much influenced by his views on the role of probability in quantum theory, and he also wrote an insightful critique of the 1936 paper of Birkhoff and von Neumann on nondistributive quantum logic1 (BNIQM).

This collection of essays on the work of Sir Karl Popper is based on the Royal Institute of Philosophy’s annual lecture series given in London from October 1994 to March 1995. Popper himself died in August 1994, shortly before the start of the lectures. His death was the cause of sadness to all of those involved in the series. Some, indeed, had been close friends of Popper over many years, and others colleagues and acquaintances, some close, some more distant. Even those unacquainted with Popper personally spoke in their lectures of the profound intellectual stimulation they had received from the study of his works.

In his seminal The Poverty of Historicism1 (hereafter PH) Sir Karl Popper deployed a number of arguments to prick the pretensions of those who thought that they were, or could come to be, in possession of knowledge of the (social) future. These ‘historicists’ assumed that they could lay bare the law of evolution of a society, and that their possession of knowledge of such a law justified (large-scale) political action which had the aim of removing obstacles to the progress of history. In arguing against historicism Popper was clearly motivated by his interest in removing the intellectual backing for such revolutionary political practice.