 Dummett (1973 [1981]) also aims to develop and precisify a broadly Fregean approach to category distinctions. Frege leaves the distinction between so-called ‘proper names’ and other parts of speech merely intuitively understood, but Dummett argues that, e.g., one could make a start at criteria for distinguishing proper names by requiring substitutability of terms while preserving the well-formedness of a sentence (which, as we have seen in §1.3, also plays a role in Husserl’s distinction of meaning categories), and while preserving the validity of various patterns of inference (where the latter requirement is needed to distinguish proper names from other substantival terms such as ‘someone’ and ‘nobody’) (1973 [1981], 58 ff.). (For further refinements of these criteria, see Dummett (1973 [1981], 61–73) and Hale (1987, Chapter 2).)