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34 THE EPISTEMOLOGICAL WORKSBesides, the Popper of the 1930s used a language, style and referencesgeared to other scholars of the same problem, whereas the maturePopper was already accustomed to the more heterogeneous audiencethat attended his classes and lectures.The only way of solving the web of problems linked to induction is toprovide a different criterion of demarcation between the empiricalsciences and other forms of knowledge. Popper points out in thisconnection that ‘inductive method, like the criterion of verifiability,implies a faulty demarcation’ (CR: 53). To ‘avoid the pitfalls of theproblem of induction’, it is necessary to take into account ‘theasymmetry between verification and falsification […] which resultsfrom the logical relation between theories and basic statements’ (LSD:265). It must also be borne in mind that particular propositions arecompletely decidable from an empirical point of view: that is, they canin principle be assigned a secure truth-value, whereas universalpropositions are only partly decidable in that experience ‘can decideonly about one of the two values, about the truth or the falsity of thestatement itself’ (BG: 307). For the laws of nature are only falsifiable,but the negations of rigorously general statements about reality mayonly be verified, never definitively falsified. Thus the statement ‘It is nottrue that all swans are white’ can never be falsified, because experiencewill never be able to prove that all swans are white. The exclusion ofinduction from the characteristic procedures of science does not mean,however, that science can do without inductive direction— that is, thekind of reasoning which moves from theories with a low level ofuniversality to ones with a high level of universality. Popper calls thistendency ‘quasi-inductive’, because although it is rigorously deductive,it leads to a more general statement. These points risk appearing otiose,if not actually contradictory, in the account given in Die beidenGrundprobleme (BG: 327–328). But they may become clearer whencompared to similar pages in The Logic of Scientific Discovery, wherethe author says that:to obtain a picture or model of this quasi-inductive evolution ofscience, the various ideas and hypotheses might be visualized asparticles suspended in a fluid. Testable science is the precipitationof these particles at the bottom of the vessel: they settle down inlayers (of universality). The thickness of the deposit grows withthe number of these layers, every new layer corresponding to atheory more universal than those beneath it. As the result of thisprocess, ideas previously floating in higher metaphysical regions