Every speech community needs to be able to anchor the situations and actions communicated in language according to the parameters of time and reality. In addition to adverbial Modification as described in Chapter 10, languages tend to have well-oiled grammatical systems for accomplishing these important functions. In English there are three grammatical paradigms that relate to the domains of time and reality. These paradigms are usually described as tense, aspect, and mode (TAM for short) – tense expresses the time of discourse world situations in relation to some reference point, usually the time of speaking; aspect describes the internal temporal “shape” of a situation; while mode relates the speaker's commitment to the probability that the situation is real, necessary, or likely. It is reasonable to treat these three paradigms together for a couple of reasons. First, they constitute the main categories of Inflection on verbs and auxiliaries. Second, these paradigms interact with each other significantly, as we will see in the following pages. It would be very difficult, and even misleading, to treat each of them separately without mentioning the others.

Figure 12.1 illustrates in a general way the relationship between the conceptual domains of relative time, temporal “shape,” and reality on the one hand, and the grammatical categories of tense, aspect, and mode on the other.