Mood
Mood (or modality) is usually divided into two broad categories: epistemic and deontic. As we saw in Chapter 11, epistemic modality is a type of grammatical marking that encodes the speaker’s judgement relating to his or her knowledge about the possibility, likelihood or certainty of the proposition expressed by the sentence. This is what the English modal verbs will, can and might express in the sentences in (11).
Deontic modality expresses the speaker’s judgement relating to obligation (moral or social), permission or prohibition. This is what the English modal verbs must and should express in the examples in (12).
However, the English modal verbs cannot be divided neatly into two categories according to which type of modality they express because their interpretation can be rather fluid and depends on the context in which they occur. For example, must expresses epistemic modality in example (13a) and can expresses deontic modality in example (13b).
As we saw in Chapter 14, the modal auxiliaries do not inflect in the usual way for tense or aspect (*musted,* musting), nor do they have a third person singular -s form (*she musts). Modals also lack an infinitive form (*to must), and must occur as the first verb in a verb string (*I am musting . . .), followed by the bare infinitive form of the next verb in the string (*she must went). With the exception of must, the English modals occur in pairs (can – could; may – might; shall should; will – would). These are traditionally described as present and past tense forms on the basis of ‘sequence of tense’ patterns. For example, a past tense verb in a main clause tends to require a past tense verb in a complement clause; compare (14a) with (14b). As examples (14c) and (14d) show, the modals sometimes pattern in a similar way.
However, it is worth observing that what might be called ‘past’ modal forms are not restricted to past tense contexts, which means that the traditional classification of modals into ‘past’ and ‘present’ forms is not a matter of consensus. For example, consider uses like I’d like to help or I could do it if you’d let me. Despite these difficulties in pinning down the tense properties of the modal verbs, they are usually referred to finite verb forms because they pattern together with tensed verb forms in licensing a main clause verb string. As we will see, this ‘licensing’ is conceived in terms of grounding in Cognitive Grammar.
