On October 25, 1946, Karl Popper read a controversial paper at the small Moral Sciences Club of the University of Cambridge in England. It was a private discussion club. Its most distinguished personality was Ludwig von Wittgenstein (1889-1951), one of the pillars of 'linguistic philosophy', then an important school in England, soon to have many followers in the United States. This way of practicing philosophy was launched at the Vienna Circle by Moritz Schlick between the two World Wars. Popper took the invitation to speak at the Cambridge Club as an excellent opportunity to confront Wittgenstein, the champion of linguistic philosophising, a practice which Popper, since his youth in Vienna, considered nothing less than frivolous. Popper's admired Bertrand Russell was also a regular attendant; Popper considered him an ally in his fight against linguistic philosophy and positivism and wanted to strike a deeper acquaintance with him on the occasion of the seminar.
Let us imagine the scene. It was cold in the room where the Club met. Post-war restrictions made for a miserly coal-fire, barely kept alive with a poker. Thanks to the fascinating book by David Edmonds and John Eidinow, Wittgenstein's Poker (Harper Perennial, 2001) we know as much as can be known of the meeting that day. Popper wanted to give his talk the title: "Do philosophical problems exist?" Popper thought that philosophy dealt with, and should deal with, true problems. So he wanted to attack Wittgenstein, who, on the contrary, maintained that there were no problems in philosophy, only verbal puzzles.
For Wittgenstein, the philosopher's task was to clarify concepts, correct the use of words, solve verbal confusions, and thus "help the fly to get out of the bottle". That was the task Wittgenstein set himself in his first book, the Tractatus Logico-Philosophicus (1922). Later, in papers posthumously collected as Philosophical Investigations (1953), he moved from wanting philosophers to solve philosophical confusions by using a language without ambiguities to doing so by following popular usage. In any case, he held by the doctrine of the Vienna Circle that propositions with sense could only be of two kinds: analytic propositions, meaning logical and mathematical tautologies; and empirical propositions, verifiable by observation. Everything else was senseless metaphysics.
Popper, on the contrary, always believed that philosophers should face real problems, even if they could not solve them completely: problems such as the failings of induction, the nature of probability, the relationship between cause and effect, the possibility of free will, the sense of ethical propositions, or the dangers of expressivism in music. (I well remember how he always asked, when we proposed a piece of research, "What is your problem?" and how he admonished us that a problem is not fully understood until it is solved.) Indeed the whole of the logic of scientific discovery to which Popper dedicated a great part of his time, is 'metaphysical' but still full of sense and import.
Edmunds and Eidinow relate that as soon as Popper made the first move, Wittgenstein got up to monopolise the conversation, as was his habit. He started to shout, as also was his habit, stressing his exclamations of "Popper, you are wrong!" by jabbing the air with his poker. Nobody seems to know what really happened at that point. It seems a voice was heard (some witnesses say it was Russell's): "Wittgenstein, put that poker down!" Neither do we know whether what caused Wittgenstein's brusque exit banging the door, as again was his habit, was Popper's reply to a question from the floor: "Give us an example of an ethical rule." Popper answered, "Do not threaten visiting lecturers with pokers".
In his doctoral dissertation of 1928 and his Logic der Forschung (1934), Popper had posed and partly solved a number of fundamental problems of the theory of knowledge. The first was on the demarcation line set by the positivists of the Vienna Circle between meaningful and senseless propositions: their demarcation line between the two was whether they were empirically verifiable, if they were not they were senseless. For Popper, there were non-verifiable propositions that made sense, especially ethical and esthetic propositions. His demarcation line was not between meaningful and nonsensical propositions but between scientific propositions (refutable) and non-scientific (that one did not know how to refute).
The second problem fundamentally solved by Popper was the problem of induction. David Hume had pointed out that we could not be sure that the sun would rise tomorrow just because it had done so as far back as one could remember. Popper generalised this by saying that it was impossible to assert the truth of a theory by the repeated observation of its instances; it was only possible to refute it when its predictions turned out to be false. One could only assert for sure the proposition that all swans were white by induction after having observed all past, present and future swans, not a very fruitful methodology. From this Popper drew two fundamental conclusions: that it was a mistake to aim at certainty; and that knowledge did not advance through verification or confirmation of hypotheses, but by attempts to refute them.
I vividly remember my excitement when I heard Popper 'solve' the problem of induction in class. My teachers in Madrid had always explained to me that the method of science was a combination of induction and deduction. Not so! You should have seen me speaking aloud and waving my arms in the surrounding streets of the London School of Economics: science is not inductive! (There were no mobile phones then, so the passers-by must have thought I was deranged.)
As Popper himself pointed out, the solution of one problem poses new ones. The scientific method is more than mechanically applying the hypothetic-deductive method. Refutation is rarely final and sometimes one must hold to a 'refuted' theory to give it a run for its money. But this is for another day. I only want to leave this topic with the literary image on the frontispiece of the Logic of Scientific Discovery (1959): "Theories are nets: only who throws them will catch. Novalis".
I was in the third year of my Law studies in Madrid when a book caught my attention in a bookshop. It was called The Open Society and its Enemies (1945, 1957). On its cover, that Spanish edition carried the portraits of three of those enemies: Plato, Hegel, and Karl Marx. I flipped through its pages, looked at the introduction and the table of contents. I could not make heads or tails of the presence of those three illustrious philosophers on the cover of an essay criticising them. Fast forward. One day I was walking down the corridor towards the refectory when I saw this sign on a door: "K.R. Popper". I knocked and asked the diminutive professor behind the desk, "Are you the author of The Open Society?" So started a great and fruitful friendship.
The book was a sensation in the United States and the United Kingdom when published in 1945. Popper told me once that after the Anschluss he asked himself whether he should try to kill Hitler. He decided to try to destroy the philosophy embodied in the Führer instead. It caused a scandal in academic circles because of the impassioned work of demolition of those three revered figures. Popper dared present Plato as a reactionary enemy of Athens and friend of Sparta, and Hegel as an obscurantist servant of the Prussian State—pure blasphemy! He was accused of an anachronistic misunderstanding of Greek culture and an incapacity to understand German philosophy. In conservative circles, there was further shock at seeing Marx treated more kindly than Plato and Hegel.
I have to take my courage in both hands to dare to differ with those critics of Popper's great book. Still, I would tell the admirers of the Republic that they should ponder the dangers of a philosopher-king and compare that dialogue with the Funeral Oration of Pericles on the commemoration of the dead of the first year of the Peloponnesian War. If they are not yet convinced, they should read the purely Platonic dialogue of The Laws and imagine themselves in the clutches of the Nocturnal Council.
Of Hegel, what can one say that does not paint him in an even worse light than that thrown on him by Popper? Let us move in imagination to Jena in 1806, after the battle in which Napoleon crushed the Prussian army. Hegel wrote, "I saw the Emperor, the Spirit of the World, pass-by on horseback, to go and contemplate his kingdom". To the admirers of Hegel, one could say in extenuation that they must have had difficulty in understanding his peculiar German.
Popper's analysis of Marx's philosophy centres mainly on the errors of 'historicism' inherited from Hegel. Historicism lays down that history follows a necessary path. Another of my masters in Spain taught me that the object of social science was to predict the evolution of history. Popper's lectures on historicism opened my eyes to the idea that the future has not been written. He had developed this idea in his book The Poverty of Historicism (1947), in which he distinguished two kinds of theories of history: "anti-naturalist" and "pro-naturalist". The first considered that human societies could not be studied with the methods of the natural sciences; the second that the method of physics could and should be applied to sociology. Hegelian theories belonged to the first kind, since for Hegel, history was the development of the mind or reason. The second kind was proposed by Auguste Comte, for whom the observation of positive data showed that human societies necessarily progressed towards comprehensive and centralised organisations.
From the logical point of view, Popper was in the end content with saying that "we could not predict, by rational or scientific methods, the future of our scientific discoveries". If we could, they would not be future. This consideration is also applicable to technology, as the experience of the last fifty years abundantly shows.
One reason why Popper treated Marx so considerately is that Marx unwittingly produced a testable theory of the necessary trend of capitalism towards monopoly and the inevitable immiseration of the working class—and that this theory had been proven false by the path followed by Western society and by the horrors inflicted on millions by Marx's disciples. There was also Popper's soft spot for social-democracy, well documented by Malachy Hacohen (2002), which inclined Popper to lament the cruelty of early capitalism and to show preference for the welfare state.
My conversations with Popper later in life threw light on some of our differences on economic questions. To his proposal that social reform should never be wholesale and always open to trial and error he gave the unfortunate name of "piecemeal engineering", which gave the impression that he was ready to have politicians and bureaucrats shape society from above. As time passed, however, the shortcomings and difficulties of the welfare state made him more sceptical of the promises made in the aftermath of the war. We still differed on the shortcomings of free markets, which he thought were larger than I believed. We also differed on his reformulation of utilitarianism, whose measurement difficulties he thought he had solved by substituting minimising pain for maximising communal pleasure. Still, I now think that the logical impossibility of moving from facts to values can be solved by analogy with the refutation of hypotheses. But this again is for another day.
Under the influence of his lifelong friend Friedrich Hayek, he came to view social science as necessarily an evolutionary theory, which is clearly a move in the right direction. He was interested in Darwinism from its early days, as a 'metaphysical' theory that nevertheless provided a suggestive framework for biology and sociology. He always rejected teleological interpretations of evolutionism.
My past criticisms of his doctrines do not detract from my gratitude to Sir Karl Popper for all he taught me over the years and for the treasure of his friendship. I think of all this when I hear my wife and my daughter sing by the piano that the great philosopher bequeathed them.