This book introduces Karl Popper's theory of how science advances. Published in the original German in 1934, with the English edition arriving in 1958. Popper's writing style is probably the most clear and interesting of any philosopher I have read. I understand his books almost completely -- except his mathematical proofs, which are beyond me no matter who writes them. The book is thick (544 pages), but I read it through. While the concepts are extremely simple, the argumentation is quite intense.

The detail was overwhelming at times. It's not a casual philosphy book.

Popper is a philosopher of grand theories. At the start of the preface, he claims that "all science is cosmology". I can relate, because I think it is all software, or as John Wheeler says, "it's a bit". While I do pretend to understand the first thing about the cosmology of the Universe, I do think there's a cosmology of Software (all software). Therefore, I think there are many lessons to be learned from Popper. What disappoints me is that my computer science curriculum did not include a discussion of Popper's Logic of Scientific Discovery. I guess I would have been to young and impatient to understand such a course, anyway.

[p10] It should be noticed that a positive decision can only temporarily support the theory, for subsequent negative decisions may always overthrow it. So long as theory withstands detailed and severe tests and is not superseded by another theory in the course of scientific progress, we may say that it has 'proved its mettle' orrhat it is 'corroborated' by past experience.

Nothing resembling inductive logic appears in the procedure here outlined. I never assume that we can argue from the truth of singular statements to the truth of theories. I never assume that by force of 'verified' conclusions, theories can be established as 'true', or even as merely 'probable'.

The problem with any epistemology is that it cannot prove itself. Some people think that Popper claims that his proposals are provable, and he argues with such forcefulness that he seems certain they are true, and may have even fooled himself into their being true. However, I think that's true of many of the philosopher's of science, and this doesn't mean his theory is not useful on its own. Popper was a lightning rod for criticism, and I think unfairly so. He was so certain, I think, that it was easy to mock him with relativistic arguments ("we never know anything for certain"), which might also be true, but did not devalue his theories themselves as well as their usefulness as an approach to scientific discovery.

[p15] Thus I freely admit that in arriving at my proposals I have been guided, in the last analysis, by value judgments and predilections. But I hope that my proposals may be acceptable to those who value not only logical rigour but also freedom from dogmatism; who seek practical applicability, but are even more attracted by the adventure of science, and by discoveries which again and again confront us with new and unexpected questions, challenging us to tryout new and hitherto undreamed-of answers.

[p37] The empirical sciences are systems of theories. The logic of scientific knowledge can therefore be described as a theory of theories.

Scientific theories are universal statements. Like all linguistic representations they are systems of signs or symbols. Thus I do not think it helpful to express the difference between universal theories and singular statements by saying that the latter are 'concrete' whereas theories are merely symbolic formulae or symbolic schemata; for exactly the same may be said of even the most 'concrete' statements.

Theories are nets cast to catch what we call 'the world': to [p38] rationalize, to explain, and to master it. We endeavour to make the mesh ever finer and finer.

Testable software is better, because we can define how it will behave. That doesn't mean we have written all the possible tests for the program. Rather, we can write tests, and the more we write, the more reliable the software will be. If we can't even think of how to test software, how would we know if it begins to satisify our customer's requirements.

[p128] Above all, our theory explains why simplicity is so highly desirable. To understand this there is no need for us to assume a 'principle of economy of thought' or anything of the kind. Simple statements, if knowledge is our object, are to be prized more highly than less simple ones because they tell us more; because their empirical content is greater; and because they are better testable.

[p280] The old scientific ideal of episteme--of absolutely certain, demonstrable knowledge-has proved to be an idol. The demand for scientific objectivity makes it inevitable that every scientific statement must remain tentative for ever. It may indeed be corroborated, but every corroboration is relative to other statements which, again, are tenative. Only in our subjective experiences of conviction, in our subjective faith, can we be 'absolutely certain'.

[p281] With the idol of certainty (including that of degrees of imperfect certainty or probability) there falls one of the defences of obscurantism which bar the way of scientific advance. For the worship of this idol hampers not only the boldness of our questions, but also the rigour and the integrity of our tests. The wrong view of science betrays itself in the craving to be right; for it is not his possession of knowledge, of irrefutable truth, that makes the man of science, but his persistent and recklessly critical quest for truth.

Has our attitude, then, to be one of resignation? Have we to say that science can fulfil only its biological task; that it can, at best, merely prove its mettle in practical applications which may corroborate it? Are its intellectual problems insoluble? I do not think so. Science never pursues the illusory aim of making its answers final, or even probable. Its advance is, rather, towards an infinite yet attainable aim: that of ever discovering new, deeper, and more general problems, and of subjecting our ever tentative answers to ever renewed and ever more rigorous tests.

[p282] (4) The pragmatic problem of induction solves itself: the practical preference for the theory which in the light of the rational discussion appears to be nearer to the truth is risky but rational.

(5) The psychological problem (why do we believe that the theory so chosen will continue to be worthy of our trust?) is, I suggest, trivial: a belief or trust is always irrational, but it may be important for action.