We are able to participate in countless different sorts of social practice. This indefinite set
of capacities must be explainable in terms of a finite stock of capacities. This paper
compares and contrasts two different explanations. A standard decomposition of the
capacity to participate in social practices goes something like this: the interpreter arrives
on the scene with a stock of generic practice-types. He looks at the current scene to fill-in
the current tokens of these types. He looks at the current state of these practice tokens to
see what actions are available to him. He uses his current desires to choose between these
various possible actions. I argue that this standard explanation is defective, drawing on
arguments by Searle and Wittgenstein and Garfinkel. I propose an alternative
explanation, in which the participants must continually show each other the state of the
scene in order to maintain the scene’s intelligibility. I provide a simple formal language in
which to describe this alternative approach, in which we can state quite precisely what
someone is (and should be) doing when they participate in a practice. This language is
related to both deontic and epistemic logics, but it is much simpler – it does not include
the classic propositional connectives, and it is driven by a very different set of
assumptions. The inspirations for this formal language are Searle’s analysis of directions of
fit, Wittgenstein’s remarks on rule-following and Garfinkel’s ethnomethodology.
