20101108131129231

32 THE EPISTEMOLOGICAL WORKSthe problem from an evolutionist standpoint in the light of his newtheory of the three worlds (that is, in the essay forming Chapter 1 ofObjective Knowledge). On the one hand, then, Popper finds convincingHume’s critique of inductive inference, on the grounds that nothinglogically justifies the move from observed facts to laws; but on theother hand, he cannot accept Hume’s psychologi cal explanation ofinduction in terms of habit derived from repetition.As regards the logical aspect, Hume correctly pointed outinnumerable apparent regularities which everyone trusts in practice, andupon which scientists themselves base their theories. Such practice,however, conflicts with what Popper calls the principle of the invalidityof induction: namely, that ‘there can be no valid reasoning fromsingular observation statements to universal laws of nature, and thus toscientific theories’ (P1:32). If we refer to repetitive induction orinduction by enumeration, which is based upon the repetition ofobservations, then its invalidity is obvious enough: ‘no amount ofobservation of white swans establishes that all swans are white (or thatthe probability of finding a non-white swan is small)’ (MF: 104). Nordoes ‘eliminative induction’ fare any better—that which aims ateliminating every false theory so as to establish the true one, as Baconand Mill prescribed. For its proponents did not realize that the number oflogically possible rival theories is always infinite.The principle of the invalidity of induction also appears to clash withthe principle of empiricism: namely, that ‘we demand that our adoptionand our rejection of scientific theories should depend upon the results ofobservation and experiment, and thus upon singular observationstatements’ (P1:32).’ Hume tried to solve the conflict by abandoningrationalism: if induction is not rationally justified and yet works, all wehave to do is give up any appeal to reason and explain it in terms ofhabit. Popper, however, prefers to give up induction and to saverationalism by means of a further principle: ‘We demand that ouradoption and our rejection of scientific theories should depend upon ourcritical reasoning (combined with the results of observation andexperiment)’ [ibid.]. This principle of critical rationalism allows us tosolve the Humean problem without relying exclusively upon thepsychological explanations that Popper regards as unfounded.Humean psychology, being a reformulation of diffuse popularbeliefs, seems to Popper to be mistaken with regard to (a) the typicalresult of repetition, (b) the genesis of habits, and (c) the expectation ofregularity characterizing both experiences and behaviour (CR: 43).First, it has to be said that repetition often results not in a conscious