By any standard, Sir Karl Popper is one of the greatest philosophers of our century. In the first place, he is, side by side with Bertrand Russell, one of the few representatives of the tradition of Greek philosophy which began with Thales and was amplified by what he called the "great generation" of thinkers in Athens in the 5th century, which included Protagoras, Democritus and Socrates, and also by Aristotle. Throughout his long career as a philosopher, he has tried his best to have his own world view and to determine the place of Man in the universe. He endeavoured to learn as much as possible from modern and contemporary sciences and to make it clear that Man, in spite of his infinitesimal physical size in the universe, is an incredible product of biological evolution that is able to determine his own place in the world.
In the second place, he was an important historian of Western philosophy. His monumental work, The Open Society and its Enemies, which happened to be published in the same year (1945) with Russell's A History of Western Philosophy, is popularly regarded as a critique of totalitarianism. This view is true, but, it is much more than that. It is a completely new interpretation of Western philosophy. His critical re-examinations of Heraclitus, Plato, Aristotle and Hegel and Marx, in particular, are extremely original and challenging. The fact that it is still widely read in France, Italy, The Netherlands, Japan and also in Russia and some former Marxian countries shows that The Open Society has been influential for almost a half century.
In the third place, Sir Karl was an important and highly influential philosopher of science. The fact that he and Russell were the only philosophers of this century who became fellows of the Royal Society is not accidental. He was also a foreign member of the famous Italian Accademia dei Lincei. When his first book, The Logic of Scientific Discovery, was published in German, his main interest was in physics. After the nineteen seventies, however, his interest and influence in biological sciences have steadily increased. Many important scientists, such as Sir John Eccles, Sir Peter Medawar, Konrad Lorenz, Jacques Monod, have acknowledged their indebtedness to Sir Karl.
In the fourth place, it has to be noted that the centre of Sir Karl's interest in philosophy has always been in what he called science of knowledge. In this respect, too, he was an orthodox representative of the great tradition of philosophy from the ancient Greeks up to Kant. He is regarded, side by side with his friend Lorenz, as a founder of what is now called evolutionary epistemology.
Last but not least, though he was born and brought up in Vienna, his prose was always a model of clarity, both in German and in English. He once told me that he tried to write English as Russell did. It is remarkable that The Open Society was already written with incredible lucidity and elegance. Russell's style is very clear, witty and sometimes staccato. Sir Karl's style was also clear, elegant and more legato.
Requiescat in pace.