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logical type

Subject Philosophy

DOI: 10.1111/b.9781405106795.2004.x


L ogic Words or expressions can be classified into a hierarchy of classes , such as individuals, classes, class of classes, and so on. The logical type of a word or an expression is the class it is in. When two words a and b are of the same logical type, for any sentential function F x , F a and F b are either both meaningful or both meaningless. In “Socrates is a philosopher” and “Aristotle is a philosopher,” “Socrates” and “Aristotle” are of the same logical type, for both of them are individuals. Yet this does not extend to “A man is a philosopher.” For “man” is a class, and hence is of a different type. “The definition of a logical type is as follows: A and B are of the same logical type if, and only if, given any fact of which A is a constituent, there is a corresponding fact which has B as a constituent, which either results by substituting B for A, or is the negation of what so results.” Russell, Collected Papers of Bertrand Russell , vol. IX ... log in or subscribe to read full text

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