Besides being a great quote, this shows how philosophy is based on science.
“First, although in science we do our best to find the truth, we are conscious of the fact that we can never be sure whether we have got it. We have learned in the past, from many disappointments, that we must not expect finality. And we have learned not to be disappointed any longer if our scientific theories are overthrown; for we can, in most cases, determine with great confidence which of any two theories is the better one. We can therefore know that we are making progress; and it is this knowledge that to most of us atones for the loss of the illusion of finality and certainty. In other words, we know that our scientific theories must always remain hypotheses, but that, in many important cases, we can find out whether or not a new hypothesis is superior to an old one. For if they are different, then they will lead to different predictions, which can often be tested experimentally; and on the basis of such a crucial experiment, we can sometimes find out that the new theory leads to satisfactory results where the old one breaks down. Thus we can say that in our search for truth, we have replaced scientific certainty by scientific progress. And this view of scientific method is corroborated by the development of science. For science does not develop by a gradual encyclopaedic accumulation of essential information, as Aristotle thought, but by a much more revolutionary method; it progresses by bold ideas, by the advancement of new and very strange theories (such as the theory that the earth is not flat, or that ‘metrical space’ is not flat), and by the overthrow of the old ones.
But this view of scientific method means that in science there is no ‘knowledge’, in the sense in which Plato and Aristotle understood the word, in the sense which implies finality; in science, we never have sufficient reason for the belief that we have attained the truth. What we usually call ‘scientific knowledge’ is, as a rule, not knowledge in this sense, but rather information regarding the various competing hypotheses and the way in which they have stood up to various tests; it is, using the language of Plato and Aristotle, information concerning the latest, and the best tested, scientific ‘opinion’. This view means furthermore, that we have no proofs in science (excepting, of course, pure mathematics and logic). In the empirical sciences, which alone can furnish us with information about the world we live in, proofs do not occur, if we mean by 'proof an argument which establishes once and for ever the truth of a theory. (What may occur, however, are refutations of scientific theories.) On the other hand, pure mathematics and logic, which permit of proofs, give us no information about the world, but only develop the means of describing it. Thus we could say (as I have pointed out elsewhere ): ‘In so far as scientific statements refer to the world of experience, they must be refutable; and, in so far as they are irrefutable, they do not refer to the world of experience.’ But although proof does not play any part in the empirical sciences, argument still does; indeed, its part is at least as important as that played by observation and experiment.”
Karl Popper, ‘The Open Society and Its Enemies’, Chapter 11.