there can be no such catalogue; but one would settle for a list of categories, that is, of the kinds of entities to which we refer or might have occasion to refer. But then, every serious philosopher claims that he can in his fashion talk about everything. So one could not hope to reconstruct the various ontological theses by means of a list of all descriptive signs. The equivalent of the classical problem is, rather, the search for the undefined descriptive signs of the ideal language. 1 I used this idea implicitly when I explicated nominalism and phenomenalism. To show that it is reasonable, also historically, consider two more examples. Take first materialism or, as it now styles itself, physicalism or philosophical behaviorism. Interpreted fairly, even this silliest of all philosophies asserts no more than that all mental terms can be defined in a schema whose undefined descriptive predicates refer to characters exemplified by physical objects. Quite so. I, too, am a scientific behaviorist. Only, the maferialist's schema is, rather obviously, incomplete and therefore not, as he would have to assert, the ideal language. Russell, on the other hand, when he denied the existence of classes, meant, not at all either obviously or sillily, no more than that class names are defined signs of the ideal language.
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