There is one purely logical problem in regard to which these difficulties are peculiarly acute. I mean the problem of generality. In the theory of generality it is necessary to consider all propositions of the form f ⁡ x where f ⁡ x is a given propositional function. This belongs to the part of logic which can be expressed, according to Mr. Wittgenstein’s system. But the totality of possible values of x which might seem to be involved in the totality of propositions of the form f ⁡ x is not admitted by Mr.