1. Wittgenstein writes, ‘To understand a sentence means to understand a language.’ My question is: what is a language, and what is its importance to the idea of understanding what someone has said? I want to address this question while keeping firmly in mind Wittgenstein's insistence that ‘We are talking about the spatial and temporal phenomenon of language, not about some non-spatial, non-temporal phantasm’. I believe that it is astonishingly difficult to take that insistence seriously. Rush Rhees is addressing this difficulty when he writes, ‘If the language is not everything that is said by those who speak it, it may be natural to think of it as a set of rules.’ His suggestion that this is a temptation to resist is my topic in this essay.

2. There is substantial disagreement on how we are to read the ‘rule following considerations’ and, linked with that, substantial disagreement over what truth is to be found in them. Something that is, I believe, sufficiently widely shared to be labelled ‘the standard reading’ goes something like this:

Before turning to doubts about whether this is either true to Wittgenstein or a line of thought we should endorse two preliminary comments are in order.

There is an obvious and uncontroversial sense in which my understanding what another has said is dependent on a background of past use.