chapter  15
21 Pages

Grue

At the level of description, there is no doubt that one common inductive practice we take to be rational is to project common properties from samples to populations, to argue from certain Fs being G to certain other Fs being G. There are many ways we can try to spell out this practice in semi-formal terms: by saying 'Fa & Ga ' confirms ' (x)(Fx =:J Gx)' , or 'All examined As are B' supports 'All unexamined As are B' , or 'Fa1 & . . . & Fan' gives a good reason for 'Fan+/ , and so on. The precise way chosen will not particularly concern us, and I will simply refer to the kind of inductive argument pattern reflected in the various for­ malisations as the straight rule (SR). The discussion will be restricted to the simplest case where everything in a sample, not merely a percentage, has the property we are concerned with.