This work arose from the desire to teach foreign students in North America a particular variety of language used in their disciplines (speech situations), whereupon the inadequacy or non-existence of previous study became apparent. Given this raison d'être, the work first illustrates one approach to the analysis of language in order to test whether something of significance can be said about the typology of texts and discourse. The approach chosen is Systemic Functional Grammar, with its roots in the Prague School of Linguistics and the London School of J.R. Firth, a theory that is particularly able to show how situational factors affect codal choices. Secondly, the author proceeds to use this theory and one language variety (academic speech) to illustrate the influence of speech situational components on the codal selections in the language variety. Since the impetus for the work is pedagogical, the book concludes with a brief reappraisal of the analysis model and a discussion of some of the pedagogical implications stemming from the analysis. Since the work is also theoretical, the implications of the study for the model of grammar are thoroughly explored.