This paper discusses a recurring problem in the development and application of models of grammar: That of deciding which linguistically relevant contextual information forms part of (i.e. enters) the grammar, and which contextual information interacts with the grammar without being part of it. More specifically it considers the active-passive alternation in English within the framework of Functional Discourse Grammar. First, the possible factors recorded in the literature as determining the choice between an active and a passive construction are discussed. On the basis of an in-depth discussion of authentic examples it is concluded that the major determinant triggering the use of one of the two variants is not a single factor, but rather the composite notion of Speaker’s perspective, a systematically encoded cognitive notion covering a number of communicatively relevant (pragmatic and semantic) factors. Subsequently, it is argued that since the Speaker’s choice of perspective is the result of a cognitive process it is plausible to assume that this process takes place at a preverbal level, i.e. within the Conceptual Component. Since, however, in choosing the perspective the Speaker clearly draws on contextual information, stored in the Contextual Component, it can be concluded that information from the Contextual Component enters the Grammatical Component through the Conceptual Component), thereby indirectly influencing the choice of a particular grammatical construction.