Wittgenstein's answer is that it is a certain kind of rule-governed employment; and therefore he pays such an attention to the concepts of rule and rule following: For Frege, the choice was as follows: either we are dealing with ink marks on paper or else these marks are signs of something, and what they represent is their meaning.
However, let us return to Wittgenstein's answer to the question about the peculiarity of our language games: these games, we noted, are characteristically governed by rules.
The answer is quite simple – it may be done with the help of a tool developed (it would seem) precisely to do this, namely a rule or a norm.
As far as my experience goes, the majority of people practising DRT would answer to the effect that it depicts something like the (structure of the) mental content which is expressed by the expression analyzed, or that it somehow records what is going on with speakers' and/or hearers' mental representations.
However, this is nothing but a cheap readymade universal answer - (3) is not the result of an introspection or of an extrospective 12 For details see Peregrin (1995b; 1997).
To answer this question, it is not enough to consider (3) in isolation: if it is isolated from the body of DRT, it obviously provides us with no semantic analysis at all, for any formula or diagram can successfully play the role of semantic analysatum only as a node within a large structure expounding relevant relations.
True, it is not the business of philosophers to study details of our grammar; and it is not the business of linguists to answer the philosophical questions about the nature of our language.
However, the sagest abstract philosophical conception of language is empty if it does not reflect the facts of how language really works; and the most detailed atlas of the landscape of language is impotent if it is not clear which questions it purports to answer.
The answer, crucial for the structural approach, is that it is the sameness of position within the system of language, or the sameness of 'usability' within the language game to be played.
Will this require an answer outside the game of reasoning?