Systemic Functional Linguistics (SFL) is an approach to language study developed by Michael Halliday, who from the early days had language education centrally in mind, and who still regards language education as one of most important applications of his work. SFL discusses a very large number of linguistic choices. The most recent account of SFL, Halliday and Matthiessen, runs to 786 pages. SFL recognises three main aspects of context of situation: field, tenor and mode. Field has to do with what the language is about and what kind of social activity is being enacted in the language. Tenor has to do with the participants in the language event, the speakers, writers, hearers, readers, the roles they are adopting and the relations between them. Mode has to do with the channel of communication, for example, whether the language is spoken or written. Mode has to do with channel of communication, the most obvious distinction here being between speech and writing.