 It would seem, however, that the essential characteristic of a function is ambiguity… We may express this by saying that “\(\phi x\)” ambiguously denotes \(\phi a, \phi b, \phi c,\) etc., where \(\phi a, \phi b, \phi c,\) etc. are the various values of “\(\phi x\).” … It will be seen that, according to the above account, the values of a function are presupposed by that function, not vice versa. It is sufficiently obvious, in any particular case, that a value of a function does not presuppose the function. Thus for example the proposition “Socrates is human” can be perfectly apprehended without regarding it as a value of the function “\(x\) is human.” It is true that, conversely, a function can be apprehended without its being necessary to apprehend its values severally and individually. If this were not the case, no function could be apprehended at all, since the number of values (true and false) of a function is necessarily indefinite and there are necessarily possible arguments with which we are not acquainted. (Russell 1910–13, 39–40)