THE REAL WORLD 359 



data of experience, and selected by purely objective criteria. We saw 

 in Chapter IX that this is a hopeless position. When not enforced 

 simply by cosmologic preferences, our selection is determined by the 

 purely practical eflFectiveness of theories as heuristic tools in the 

 hands of human investigators. But now consider that, presented with 

 an appearance of qualitative change, our first impulse is always to 

 conceive it in terms of the local displacements of the otherwise un- 

 changing. The heuristic eflFectiveness of corpuscular theories may 

 then be held to derive at least as much from the structure of the 

 human sense of rationality as from the structure of the "objective" 

 world those theories purportedly depict. 



The regulative and substantive principles the naive realist con- 

 siders discoveries about the world can instead be regarded as hu- 

 manly chosen conventions— as Frank regarded the principle of de- 

 terminism. Accepting that principle, we take it for granted that if a 

 given set of circumstances ( state A ) is once followed by another set 

 of circumstances ( state B ) , then state A will always be followed by 

 state B. Would we, asks Frank, ever bring ourselves to recognize a 

 failure of the ultimate principle itself, as distinct from our own fail- 

 ures in applying it? Consider, he says, some particular mechanical 

 system in which we determine all the masses, distances, etc., we con- 

 ceive relevant to determination of state A, and find it succeeded by 

 state B. Consider that in many trials we find state A reproducibly 

 succeeded by state B. Suppose then we encounter some case in which 

 state A is not succeeded by the expected state B! Failing to restore 

 determinism by enlarging the system, to allow for "external influ- 

 ences," do we then reject the principle of determinism? Certainly not! 

 We rush in with postulates of hidden factors, or "state variables," not 

 previously comprised in our description of state A. We hypothesize, 

 for example, electric or magnetic parameters that had one value in 

 earlier trials but some diflFerent value when state B was not obtained. 

 And we go on hypothesizing such complications until we have so de- 

 fined a state A' that, in all our experiments, state A' is followed by 

 state B. Here we rest content until, as may happen, we meet an ex- 

 periment in which the new state A' is not followed by state B. And 

 then once again we set to work to redefine state A', in the form of 

 state A", and so on. The principle can never fail, Frank concludes, be- 

 cause we will never let it fail. No discovered truth about the real 

 world, the principle is nothing but a humanly enforced convention. 



