I think so badly of philosophy that I don't like to talk about it. ... I do not want to say anything bad about my dear colleagues, but the profession… - Karl Popper

First, it must be admitted that certain forms of behaviour may be described as more ‘natural’ than other forms; for instance, going naked or eating only raw food; and some people think that this in itself justifies the choice of these forms. But in this sense it certainly is not natural to interest oneself in art, or science, or even in arguments in favour of naturalism. The choice of conformity with ‘nature’ as a supreme standard leads ultimately to consequences which few will be prepared to face; it does not lead to a more natural form of civilization, but to beastliness14. The second criticism is more important. The biological naturalist assumes that he can derive his norms from the natural laws which determine the conditions of health, etc., if he does not naïvely believe that we need adopt no norms whatever but simply live according to the ‘laws of nature’. He overlooks the fact that he makes a choice, a decision; that it is possible that some other people cherish certain things more than their health (for instance, the many who have consciously risked their lives for medical research). And he is therefore mistaken if he believes that he has not made a decision, or that he has derived his norms from biological laws.

A theory which is not refutable by any conceivable event is nonscientific. Irrefutability is not a virtue of a theory (as people often think) but a vice.

...The answer to this problem is: as implied by Hume, we certainly are not justified in reasoning from an instance to the truth of the corresponding law. But to this negative result a second result, equally negative, may be added: we are justified in reasoning from a counterinstance to the falsity of the corresponding universal law (that is, of any law of which it is a counterinstance). Or in other words, from a purely logical point of view, the acceptance of one counterinstance to 'All swans are white' implies the falsity of the law 'All swans are white' - that law, that is, whose counterinstance we accepted. Induction is logically invalid; but refutation or falsification is a logically valid way of arguing from a single counterinstance to - or, rather, against - the corresponding law.This shows that I continue to agree with Hume's negative logical result; but I extend it.This logical situation is completely independent of any question of whether we would, in practice, accept a single counterinstance - for example, a solitary black swan - in refutation of a so far highly successful law. I do not suggest that we would necessarily be so easily satisfied; we might well suspect that the black specimen before us was not a swan."