The inflectional categories of mood and modality have to do with a range of distinctions that include signaling the kind of speech act in which a verb is deployed. Speech acts are classically defined as things we can do with words, for example, making a statement, asking a question, or giving a command. Languages often have three moods: declarative for making ordinary statements, interrogative for asking questions, imperative for giving commands. But some languages can have other moods as well, for example, expressing a speaker’s attitude about a statement, including whether it is necessary, possible, certain, or sometimes whether it is hearsay and not necessarily true.

The now-extinct language Tonkawa (Coahuiltecan) had eight suffixes signaling different moods/modalities. Mood suffixes are shown in bold:

Another interesting distinction in mood/modality is the realis/irrealis distinction that is marked in some Native American languages. If the realis form is used, the speaker means to signal that the event is actual, that it has happened or is happening, or is directly verifiable by perception. The irrealis form, in contrast, signals something that can be imagined or thought.

In English, we have no special inflection that signals mood; questions are formed using syntactic means and intonation, imperatives deploy the uninflected verb stem without any special endings. We have a remnant of a subjunctive mood, which appears in counter-factual sentences (that is, sentences expressing something contrary to fact) like If I were an aardvark, I’d eat insects . in such sentences the subjunctive verb form is the same as the plural form of the verb (so in the sentence just given, we have were rather than was).