In the Tractatus 4.126 Wittgenstein introduces the notion of a formal concept which, he says, needs to be distinguished from the notion of a proper concept, i.e. a concept such as that of “man” which has an ordinary empirical application. The sense in which formal concepts are formal is not that they have anything in particular to do with formal logic or logical form, but that they are concerned with what Wittgenstein called the “form of representation”. That is to say that they are concerned with the ways in which expressions can represent the world. To put it in another way, they are concerned with the use or application to which expressions might be put. (It is sufficiently clear, I think, that a large part of the Tractatus might be rewritten in these terms, in such a way as to leave it consistent with the later Wittgenstein.) Now, it is well known that for the Wittgenstein of the Tractatus it was impossible to say anything about the form of representation of any expression: this could only be shown. Hence Wittgenstein calls these formal concepts “pseudo–concepts”, meaning by this not that there are not such concepts, but that they are incompatible with his theory.