 The single most obvious and pervasively important situating parameter is what is (pragmatically) presupposed, the set of propositions whose truth is mutually assumed for current conversational purposes. Yet it is easy to make a case for regarding who is speaking, who is being addressed, the time of speaking, relations of relative salience, etc, as additional situating parameters. In fact, the parameters to which the contents of various special “context-sensitive” words and phrases are most obviously sensitive appear to be among the situating parameters mutual knowledge of which is essential to unconstrained conversational coordination more generally. So perhaps we should think of sentence types as expressing propositions, and of word and phrase types as expressing propositional constituents or contents, relative to one or another assignment of values to the various situating parameters that govern ongoing conversational exchange, which will then proceed more or less as follows: