  Realism is not without its problems, as was noted in §5 above. Also favoring nominalism is Occam's principle which would have us prefer theories with fewer sorts of entities, other things being equal.  The main problem for nominalists is to account for our apparent theoretical commitment to types, which, whatever types are, are not spatio-temporal particulars (according to nearly everyone). Traditional nominalists argued (as their name implies) that there are no general things, there are only general words, and such words simply apply to more than one thing. But this is not a solution to the current problem, presupposing as it does that there are word types—types are the problem. (Attempts to avoid this are given by Goodman and by Sellars; see below.) So-called class nominalists hold that a word type is just the class, or set, of its tokens. But this is unsatisfactory because, first, as we saw in §5, classes are ill-suited for the job, since classes have their membership and their cardinality necessarily, but how many tokens a type has is usually a contingent matter. (For the same reason, mereological sums of tokens are unsuited for the job of types, as they have their parts essentially.) And second, classes are abstract objects too, so it is hard to see how this is really a form of nominalism about abstract objects at all.