The essays and lectures of which this book is composed are variations upon one very simple theme—the thesis that we can learn from our mistakes. They develop a theory of knowledge and of its growth. It is a theory of reason that assigns to rational arguments the modest and yet important role of criticizing our often mistaken attempts to solve our problems. And it is a theory of experience that assigns to our observations the equally modest and almost equally important role of tests which may help us in the discovery of our mistakes. Though it stresses our fallibility it does not resign itself to scepticism, for it also stresses the fact that knowledge can grow, and that science can progress—just because we can learn from our mistakes.
The way in which knowledge progresses, and especially our scientific knowledge, is by unjustified (and unjustifiable) anticipations, by guesses, by tentative solutions to our problems, by conjectures. These conjectures are controlled by criticism; that is, by attempted refutations, which include severely critical tests. They may survive these tests; but they can never be positively justified: they can be established neither as certainly true nor even as ‘probable’ (in the sense of the probability calculus). Criticism of our conjectures is of decisive importance: by bringing out our mistakes it makes us understand the difficulties of the problem which we are trying to solve. This is how we become better acquainted with our problem, and able to propose more mature solutions: the very refutation of a theory—that is, of any serious tentative solution to our problem—is always a step forward that takes us nearer to the truth. And this is how we can learn from our mistakes.
As we learn from our mistakes our knowledge grows, even though we may never know—that is, know for certain. Since our knowledge can grow, there can be no reason here for despair of reason. And since we can never know for certain, there can be no authority here for any claim to authority, for conceit over our knowledge, or for smugness.
Those among our theories which turn out to be highly resistant to criticism, and which appear to us at a certain moment of time to be better approximations to truth than other known theories, may be described, together with the reports of their tests, as ‘the science’ of that time. Since none of them can be positively justified, it is essentially their critical and progressive character—the fact that we can argue about their claim to solve our problems better than their competitors— which constitutes the rationality of science.
This, in a nutshell, is the fundamental thesis developed in this book and applied to many topics, ranging from problems of the philosophy and history of the physical sciences and of the social sciences to historical and political problems.
I have relied upon my central thesis to give unity to the book, and upon the diversity of my topics to make acceptable the marginal overlapping of some of the chapters. I have revised, augmented, and re-written most of them, but I have refrained from changing the distinctive character of the lectures and broadcast addresses. It would have been easy to get rid of the tell-tale style of the lecturer, but I thought that my readers would rather make allowances for that style than feel that they had not been taken into the author’s confidence. I have let a few repetitions stand so that every chapter of the book remains self-contained.
As a hint to prospective reviewers I have also included a review—a severely critical one; it forms the last chapter of the book, and contains an essential part of my argument which is not stated elsewhere in it. I have excluded all those papers which presuppose acquaintance on the part of the reader with technicalities in the field of logic, probability theory, etc. But in the Addenda I have put together a few technical notes which may be useful to those who happen to be interested in these things. The Addenda and four of the chapters are published here for the first time.
To avoid misunderstandings I wish to make it quite clear that I use the terms ‘liberal’, ‘liberalism’, etc., always in a sense in which they are still generally used in England (though perhaps not in America): by a liberal I do not mean a sympathizer with any one political party but simply a man who values individual freedom and who is alive to the dangers inherent in all forms of power and authority.
Berkeley, California, Spring 1962
K. R. P.