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`One of the most important documents of the twentieth century.' - Sir Peter Medawar, New Scientist.

In one majestic and systematic attack, psychologism, naturalism, inductionism, and logical positivism are swept away and replaced by a set of methodological rules called Falsificationism. Falsificationism is the idea that science advances by unjustified, exaggerated guesses followed by unstinting criticism. Only hypotheses capable of clashing with observation reports are allowed to count as scientific. "Gold is soluble in hydrochloric acid" is scientific (though false); "Some homeopathic medicine does work" is, taken on its own, unscientific (though possibly true). The first is scientific because we can eliminate it if it is false; the second is unscientific because even if it were false we could not get rid of it by confronting it with an observation report that contradicted it. Unfalsifiable theories are like the computer programs with no uninstall option that just clog up the computers precious storage space. Falsifiable theories, on the other hand, enhance our control over error while expanding the richness of what we can say about the world.

Any "positive support"for theories is unobtainable and superfluous; all we can do is eliminate error - and even this is hypothetical, though often successful. This idea is elaborated with an orchestration suggestive of someone who loves great music. (Popper loved Mozart and Bach, and took great pleasure in composing his own music.) The common idea that Popper neglected to consider whether Falsificationism itself is falsifiable is already scotched here. You can falsify a description, but not a rule of method as such (though obviously a rule can be criticized in other ways). The notion that science offers proof is now only advanced by popular treatments of science on TV and in (many) newspapers - most journalists (with a few important exceptions) are sadly completely devoid of theoretical knowledge: a side-effect of overspecializing on the immediate moment. But then, anyone can improve.

To Order
From Amazon.com (US):The Logic of Scientific Discovery

From Amazon.co.uk: The Logic of Scientific Discovery

`Probably the only book published this year which will outlive this century.' - Arthur Koestler.

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From Amazon.com (US):The Poverty of Historicism

From Amazon.co.uk: The Poverty of Historicism

"a work of first-class importance which ought to be widely read for its masterly criticism of the enemies of democracy, ancient and modern. Popper's attack on Plato, while unorthodox, is in my opinion thoroughly justified. His analysis of Hegel is deadly. Marx is dissected with equal acumen, and given his due share of responsibility for modern misfortunes. The book is a vigorous and profound defence of democracy, timely, very interesting, and very well written". - Bertrand Russell

In the Open Society Popper illustrates the points he made in The Poverty of Historicism. But it is much more than illustration. The work has controversial criticisms of the works of Plato, Hegel, and Marx, especially their historicist and totalitarian doctrines. Historicism is a loosely connected set of ideas about change. Roughly, historicism asserts that the world consists of processes not things, and is always in flux, but even so, there are laws of historical development that describe the stages we must pass through. It was Heraclitus who said "you cannot step into the same river twice, for new waters are constantly flowing in". Popper traces historicism from Hesiod, through his influence on Heraclitus's theory of change, and how the theories of Plato, Aristotle and Parmenides can all be seen as attempts to solve the problem of change that Heraclitus discovered. Magee in his book,(Confessions of a Philosopher, Weidenfeld & Nicolson, 1997) reports that many classical scholars missed the profound insights with which this book overflows because they were preoccupied by the niceties of translation of ancient texts. Popper shows how deeply metaphysical ideas work themselves out in social and political ideologies - philosophical presuppositions that, whether recognized or not, form the framework of many modern conflicts and debates.

One of Popper's main contributions to Political theory is to switch the problem from Plato's question "Who should rule?" to "How do we arrange our institutions to prevent rulers (whether individuals or majorities) doing too much damage?".

Incidentally, even though Popper labeled Marx as one of the enemies, Popper is graciously eulogistic of Marx's method. For example, Popper is most approving of Marx's focus on the systematic unintended results of intended action, upholding the autonomy of sociology - it is individuals who act, but their interaction cannot be reduced to psychological laws. For example, the laws of supply and demand are not derivable from psychology (alone). We could also say that the evolution of money or the Internet provides two more nice examples. The footnotes are as interesting as the main text. Popper regarded this book as his "war effort", and it should be commended for its presumption that rational argument is essential in the battle against the theories that lie behind irrationalism and dangerous social and political movements.

"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...Though it stresses our fallibility it does not resign itself to skepticism, for it also stresses the fact that knowledge can grow, and that science can progress - just because we can learn from our mistakes." - Karl Popper, Preface to 1st Edition, penned in 1962.

Popper reinforced this in the Preface to the 2nd Edition, penned in 1965:

"It is part of my thesis that all our knowledge grows only through the correcting of our mistakes."

In the same preface Popper makes the point that not only knowledge, but our system of aims itself can grow through a similar process of trial and error. I think it follows that life is a series of experiments: we try on (consciously or unconsciously) different values, lifestyles and ways for size, rejecting those that fail to satisfy the aims that we are using provisionally as a criterion. These criteria themselves can be subject to processes of trial and error-elimination - a higher level selection. The book applies this principle across a wide range of problems, from politics to the mind-body problem.

The book defends an objective theory of knowledge against the tradition, traceable back to Aristotle, of seeing knowledge as a subjective state of a human being, and scientific knowledge as a specially secure sort of belief. Scientific knowledge, Popper argues, is an abstract product of our minds that is detachable from and criticizable independently of its creator. My favorite metaphor for objective knowledge is a new SAAB car engine. A theory embodying scientific knowledge is like a new engine placed on the table for other SAAB designers and technicians to criticise, tweak and adjust. Once created, it can be worked on, improved or rejected, even if the designer is unknown or is no longer with us. (N.B. a scientific theory, Popper would insist, is not only an instrument, but is also either true or false.)
Popper makes major use of his theory of three domains: World 1 (the world of physical objects and processes), World 2 (our psychological states), and World 3 (the world of abstract products of the mind that are not reducible to our psychology). Examples of World 3 objects are numbers, theories, designs, works of art, institutions, Web authoring programs, SAAB engines. Many reviewers have been distracted by the fact that some things belong to more than one of these domains. But the interesting question is not whether these are exclusive domains, but how they interact with one another and whether this thesis solves the problems it addresses. Popper conjectures that it is only through World 2 that World 3 objects can influence World 1.

An intellectual autobiography spanning Popper's life from his early youth up to about 1970. It provides a delightful and comprehensive introduction to Popper's work, without sacrificing any depth or detail. Besides being an absorbing exposition of his World 3 creations, Popper also talks about his personal attitude and feelings about music and about various particular and general social problems he has encountered in his life. Like The Open Society and its Enemies, the footnotes to Unended Quest are substantial and worth a serious read.

A joint effort of Popper and Eccles to produce what they describe as a modest theory of interactionism, consisting of two parts. In Part I Popper surveys the philosophical background and criticises rival theories. In Part II Eccles provides a synopsis of the then current knowledge of brain function and anatomy, and propounds a neurological theory underpinning the interaction of the mind and the brain. The theory has some counterintuitive predictions that suggest interesting experiments. The final section consists of a fascinating dialogue between Popper and Eccles. I especially enjoyed Popper's demolition of materialism, drawing on the history of science, including the field theories of Boscovich, Leibnitz, and Faraday and Maxwell.

In this connection, Popper also attacks the pervasive assumption that it is impossible or methodologically unsound to explain one sort of domain (or type of "substance") in terms of another. If the mind and body are radically different types of thing, it is said, then one cannot explain the other. This criticism was leveled at Descartes's dualism, and is still used today (see John Searle's otherwise excellent book, The Mystery of Consciousness, 1997, Granta Books: London. and my review in New Scientist).This is obviously wrong. The best explanations we have relate very different types of process or thing. For example, in physics, light is explained by relating it to the very different phenomena of magnetism and electricity. It was once thought that the moon and an apple are very different things: but Newton disabused us of this parochialism, showing that they both obeyed the same laws.
Popper further elaborates his theory of Worlds 1, 2 & 3. None of the outstanding theorists of the mind-body problem have in any way helped us to understand how abstract products like theories, numbers and the logical relationships within and between theories can make a difference to the physical world. The suggestion that you are able to read this now independently of the existence of scientific and mathematical theories and reasoning strikes me as outrageous. Yet philosophers such as Searle, Dennett, Gerald Edelman, etc., make this very suggestion through their complete neglect of this factor and of Popper's pioneering exploration of the role of abstract entities and relations.

The Postscript to The Logic of Scientific Discovery was written mainly during the years 1951-56, at the time when Logik Der Forschung was being translated into English as The Logic of Scientific Discovery. The different volumes were originally intended as a series of appendixes to The Logic of Scientific Discovery, where Popper would expand, correct and develop its ideas. But one group of appendices grew into a work far exceeding The Logic of Scientific Discovery, so it was decided to publish these as a separate work called Postscript: After 20 years. But no sooner had the text been set in typed galley proofs in 1956-57, when the project came to a halt because Popper had to have operations on both of his eyes. When he had recovered, Popper did do a great deal of work on the book, but other projects took over (completely after 1962) and the Postscript lay unpublished for decades. (Fortunately, at least some of Popper's associates and students had access to it.) The three volumes can be read separately, but bear in mind that they form a connected series of arguments. Each volume attacks one or another of the subjectivist or idealist approaches to knowledge.

• Realism and the Aim of Science, Volume I of the Postscript, Routledge, 1985. Hutchinson, 1983.

  In this volume Popper attacks Inductivism, the chief source of subjectivism and idealism (the world is my dream). His attack spans four stages: logical, methodological, epistemological, and metaphysical. Popper develops his theory of falsificationism, dealing with many misinterpretations. He makes it clear that he had always distinguished between the purely logical sense of falsifiability (which defines his demarcation criterion) and the methodological impossibility of obtaining a definitive or conclusive falsification. The former is based on a logical relationship between the theory and basic statements (statements contradicting the theory and describing observable things). Each generation of students "discovers" that Popper's criterion is not applicable because one cannot conclusively refute any theory. But Popper's point was that we must decide in advance which states of affairs (basic statements) we would accept as refutations of our theory. If I claim that all swans are white, I must be able to describe at least one circumstance which contradicts the theory and under which I would abandon my claim.

  Look out for this travesty of Popper's analysis: "You cannot prove a theory, but you can disprove it". (This is important because even Popper, when speaking roughly of his method, used the word "disprove". See page 192 of Conjectures and Refutations.) This travesty allows superficial critics to say "but to disprove a theory is simply to prove its contradictory; and if we can prove then we can be certain, but Popper told us that we cannot eliminate uncertainty, and thus Popper fails to escape the problem of uncertainty."

  This common mistake confuses demonstration and derivation. Proof is a matter of demonstration (as in mathematics), but refutation is a matter of accepting a basic statement and rejecting the truth of the theory it contradicts. If I accept "This swan here is black", then I am obliged to reject "All swans are white". Because from "This swan here is black" I can derive "Not all swans are white". But I have not proved that not all swans are white, that this must be true. In a proof, we discard the assumptions that helped us to get to the conclusion. This is quite clear in proof by reductio ad absurdum. In a reductio ad absurdum we start by assuming the opposite of what we wish to prove. That is, we assume it is false. We then try to infer an absurdity (contradiction) from this, and if we do, we then conclude that the assumption must be true. But in a refutation our rejection of a theory ("All swans are white") depends on our maintaining the truth of the basic statement ("This swan here is black"). In a refutation we hold on to the assumptions of our derivation. (Of course, the derivations involved in science are much more complex than in the swan example, but the point stands. But see Jack Cohen's paper in The Critical Rationalist.)

  Popper develops a theory of probability. In The Logic of Scientific Discovery Popper had criticized the subjectivist interpretation of probability using the frequency interpretation. In this volume, he elaborates a new interpretation called the propensity interpretation.

  True to his argumentative (though careful) style, Popper gives Thomas Kuhn a good drubbing in the Introduction. Kuhn misinterpreted Popper's criterion of demarcation as a description of the history of science. In fact, the criterion is based on a logical analysis of the relationships between theories and test statements. Kuhn thought that the actual behaviour of scientists could refute a logical criterion and undermine a methodological proposal for what scientists ought to do based on this logical criterion. Kuhn claims (page 70 of The Structure of Scientific Revolutions, 1972.) that history shows that no scientists used Popper's method and it is thus undermined. Even if Kuhn were right about the history of science, the fact that no one has used a method in no way shows it is not the best method. On the other hand Popper supplies plenty of examples that conform to his proposal.

  I would like to make a point which I guess is along Popper's lines. It would seem that in Kuhn's eyes the collective of scientists is an ultimate authority: what they do is what you should do, and vice versa. This is not what Kuhn explicitly says, but it does follow from what he does say. There is no room for the sceptic to say "well, I do respect your work, but perhaps you are wrong in your methods". But there should be room for anyone to criticise scientists, even if he is in a minority. After all, it is logically possible that the whole of science is wrong. If we forget the fallibility of scientists (even as a whole) we open the door to the emergence of an unimpeachable scientific elite and technocracy. The healthy communication and give and take between scientific specialists and nonspecialists that we often do enjoy would break down. This is the danger of the popular approach to science in philosophy called Naturalism, for which Kuhn is partly responsible, which asserts that we can only study science in terms of what scientists actually do. Along with its sociological companions, it is one of the most spineless, shallow perspectives on science.

  Popularizations of science ought to stop using the flippant phrase "scientific proof", for this only reinforces Kuhn's canonization of science. I do not think that this is an unwarranted concern. We must uphold the heroic conception of science, but we must also maintain that no one is above or outside criticism from any source. It is one of the aims of Karl Popper Forums to help scientists keep in touch with non-scientific-specialists and specialists in other fields through the medium of philosophical discussion. Philosophical discussion takes place on a level field and can help to correct any misunderstanding between scientists and others.

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  From Amazon.com (US):
  Realism and the Aim of Science
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  Realism and the Aim of Science




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• The Open Universe, Volume II of the Postscript to The Logic of Scientific Discovery, Routledge, 1988. Hutchinson, 1982.

  This work contains the most important and sustained treatment of determinism. Popper distinguishes between metaphysical and scientific determinism. Scientific determinism is the view that

  "...any event can be rationally predicted, with any desired degree of precision, if we are given a sufficiently precise description of past events, together with all the laws of nature."

  Metaphysical determinism is the view that the future is as unchangeable as the past. Metaphysical determinism is a weak implication of scientific determinism that is untestable. No matter how regular and unchangeable the world appeared, there could always be an island of changeability somewhere in, say, a distant galaxy. It is, therefore, against scientific determinism that Popper's argument is directed, because if scientific determinism falls, metaphysical determinism falls with it. He argues that not even classical physics obliges us to accept a deterministic world. The most fascinating argument for me is the argument for the impossibility of self-prediction, which is elaborated at a satisfyingly very abstract (but still very clear) level.

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  From Amazon.com (US):
  The Open Universe
  From Amazon.co.uk:
  The Open Universe

   

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• Quantum Theory and the Schism in Physics, Volume III of The Postscript, Routledge, 1989. Hutchinson, 1982.

  Popper reviews the history of quantum physics from a staunchly realist position. Popper's view is that quantum theory has been misinterpreted, and this has led us into paradoxes (such as that light consists of both particles and waves). These paradoxes arise because of a faulty understanding of the calculus of probability, which forms an important part of quantum theory. The prevalent understanding of probability is that it is a measure of our degree of belief or of our knowledge/ignorance. Popper opposes his own objective propensity interpretation of probability to this subjective view. He even proposes an experiment to test the idea that knowledge alone can effect the outcome of a quantum experiment. As in Objective Knowledge, Popper is trying valiantly and with powerful weaponry to oust the subject from physics.

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  From Amazon.com (US):
  Quantun Theory and the Schism in Physics
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  Quantun Theory and the Schism in Physics