“The central virtue of science is not that it puts forth hypotheses that are confirmed by evidence of some high degree, but that its hypotheses are capable of being refuted by evidence. It is therefore no fault in a scientist to put forward an interesting conjecture that is subsequently refuted, but it would be a fault to put forward one which then permits no refutation, or to hold one in the face of refuting evidence.
Unfalsifiable statements may be disreputable (such as pseudo-science) or of good intellectual standing (such as much of philosophy).” –from the Oxford Dictionary of Philosophy’s entry on Popper’s idea of falisfiability
“A rationalist, even if he believes himself to be intellectually superior to others, will reject all claims to authority since he is aware that, if his intelligence is superior to that of others (which is hard for him to judge), it is only in so far as he is capable of learning from criticism as well as from his own and other people’s mistakes, and that one can learn in this sense only if one takes others and their arguments seriously.
The traditional question of political theory, ‘Who should rule?’, begs for an authoritarian answer such as ‘the best’ or ‘the wisest’ or ‘the people’ or ‘the majority’. (It suggests, incidentally, such silly alternatives as ‘Who should be our rulers: the capitalists or the workers?’ analogous to ‘What is the ultimate source of our knowledge: the intellect or the senses?’) This political question is wrongly put and the answers which it elicits are paradoxical. It should be replaced by a completely different question such as ‘How can we organize our political institutions so that bad or incompetent rulers (whom we should try not to get, but whom we so easily might get all the same) cannot do too much damage?’
The question about the sources of our knowledge can be replaced in a similar way. It has always been asked in the spirit of: ‘What are the best sources of our knowledge—the most reliable ones, those which will not lead us into error, and those to which we can and must turn, in case of doubt, as the last court of appeal?’ I propose to assume, instead, that no such ideal sources exist—no more than ideal rulers—and that all ‘sources’ are liable to lead us into error at times. And I propose to replace, therefore, the question of the sources of our knowledge by the entirely different question: ‘How can we hope to detect and eliminate error?’
The proper answer to my question ‘How can we hope to detect and eliminate error? ‘is, I believe, ‘by criticizing the theories or guesses of others and—if we can train ourselves to do so—by criticizing our own theories or guesses.’
And my answer to the question ‘How do you know? What is the source or the basis of your assertion? What observations have led you to it? would be: I do not know: my assertion was merely a guess. Never mind the source, or the sources, and I may not be aware of half of them; and the origins and pedigrees have in any case little bearing upon the truth. But if you are interested in the problem which I tried to solve by my tentative assertion, you may help me by criticizing it as severely as you can; and if you can design some experimental test which you think might refute my assertion, I shall gladly, and to the best of my powers, help you refute it.
Neither observation nor reason is an authority. Intellectual intuition and imagination are most important, but they are not reliable: they may show us things very clearly, and yet they may mislead us. They are indispensable as the main sources of our theories; but most of our theories are false anyway. The most important function of observation and reasoning, and even of intuition and imagination, is to help us in the critical examination of those bold conjectures which are the means by which we probe into the unknown.
This, I believe, is the true theory of knowledge (which I wish to submit for your criticism): the theory that knowledge proceeds by way of conjectures and refutations.” -Karl Popper, from Conjectures and Refutations