In linguistics, many grammars have the concept of grammatical mood, which describes the relationship of a verb with reality and intent. Many languages express distinctions of mood through morphology, by changing (inflecting) the form of the verb.
Because modern English does not have all of the moods described below, and has a very simplified system of verb inflection as well, it is not straightforward to explain the moods in English. Note, too, that the exact sense of each mood differs from language to language.
Grammatical mood per se is not the same thing as grammatical tense or grammatical aspect, although these concepts are conflated to some degree in many languages, including English and most other modern Indo-European languages, insofar as the same word patterns are used to express more than one of these concepts at the same time.
Currently identified moods include conditional, imperative, indicative, injunctive, negative, optative, potential, subjunctive, and more. The original Indo-European inventory of moods was indicative, subjunctive, optative, and imperative. Not every Indo-European language has each of these moods, but the most conservative ones such as Ancient Greek, and Sanskrit retain them all. Some Uralic Samoyedic languages have over ten moods.
The indicative mood is used in factual statements. All intentions in speaking that a particular language does not put into another mood use the indicative. It is the most commonly used mood and is found in all languages. Example: "Paul is reading books" or "Paul reads books".
The imperative mood expresses commands, direct requests, prohibitions. In many circumstances, directly using the imperative mood seems blunt or even rude, so it is often used with care. Example: "Paul, read that book".
Many languages, including English, use the bare verb stem to form the imperative. In English, second-person is implied by the imperative except when first-person plural is specified, as in "Let's go."
The subjunctive mood has several uses in independent clauses. Examples include discussing hypothetical or unlikely events, expressing opinions or emotions, or making polite requests (the exact scope is language-specific). A subjunctive mood exists in English, but appears to be falling out of common use; many native English speakers do not use it. Example: "I suggested that Paul read books". Paul is not in fact reading the book. Contrast this with the sentence "Paul reads books", where the verb read has the third person singular ending. Another way, especially in British English, of expressing this might be "I suggested that Paul should read books.", derived from "Paul should read books." Other uses of the subjunctive in English, as in "And if he be not able to bring a lamb, then he shall bring for his trespass..." (KJV Leviticus 5:7) have definitely become archaic.
The subjunctive mood figures prominently in the grammar of the Romance languages, which require this mood for certain types of dependent clauses. This point commonly causes difficulty for English speakers learning these languages.
The conditional mood is used to express uncertainty, particularly (but not exclusively) in conditional clauses. It occurs only in main clauses and normally introduces subordinate clauses which are headed by a phrase roughly meaning 'on the condition that', such as 'if', 'as long as', etc., and these phrases can have their meaning intensified by items like 'even', as in 'even if'. The verb in the subordinate clause is marked for subjunctive modality. In English, the conditional is manifested by means of the modal auxiliary 'would' added to the bare infinitive; in other languages, such as Spanish, it is expressed by means of morphological marking on the verb. So, the conditional of 'John eats' is, in English, 'John would eat' ('would' + bare infinitive of main verb) and, in Spanish, 'Juan comerķa' (infinitive comer ((to) eat)) + third-singular ķa). Examples: I would buy a huge house if I had a lot of money (I do not have a lot money but, on the condition that I did have a lot of money, I would buy a huge house). The conditional mood is sometimes erroneously called a tense rather than a mood. This practice should be avoided, as tense refers exclusively to temporal location, and is divided three ways, into past, present and future, and therefore in no way does it involve conditions, desires, etc., which are all modal, therefore semantic, distinctions, and have no correllation with temporality. However, despite this, linguistics tends to be the only area in which such discrimination takes place, and in foreign language courses it is frequent that non-temporally-related linguistic phenomena such as the conditional mood and all aspectual (grammatical aspect) distinctions are referred to superordinately as 'tenses'.
The generic mood is used to make generalizations about a particular class of things, e.g. in "Rabbits are fast", one is speaking about rabbits in general, rather than about particular fast rabbits. English has no means of morphologically distinguishing generic mood from indicative mood, so the distinction must be made by contextual clues and linguistic experience.
The negative mood expresses a negated action. In most languages, this is not distinct mood; negativity is expressed by adding a particle before (as in Russian or Esperanto: "Li ne iras."), after (as in archaic or dialectic English: "Thou remembrest not?"), or both (as in Afrikaans or French: "Je ne sais pas.".) Standard English brings in a helper verb, do usually, and then adds not after it: "I did not go there".
In Indo-European languages, it is not customary to speak of a negative mood, since in these languages negation is originally a grammatical particle that can be applied to a verb in any of these moods. In some non-Indo-European languages, the negative mood counts as a separate mood. It could be argued that Modern English has joined the ranks of these languages, since negation in the indicative mood requires the use of an auxiliary verb and a distinct syntax in most cases. Contrast, for instance, "He sings" -> "He doesn't sing" (where the auxiliary to do has to be supplied, inflected to does, and the clitic form of not suffixed to derive the negative from "He sings") with "Il chante" -> "Il ne chante pas"; French adds the (discontinuous) negative particle ne...pas, without changing the form of the verb.
The interrogative mood is used for asking questions. Most languages do not have a special mood for asking questions, but Nenets does.
The optative mood expresses hopes or wishes and has other uses that may overlap with the subjunctive mood. Few languages have an optative as a distinct mood; Ancient Greek, Sanskrit and Finnish are three that do. Example: an ancient Greek might say "Would that Paul would read more!" with the words would that expressed by the placing the verb read in the optative mood. A contrast to this example is contemporary spoken Finnish, where the optatives -koon and -koot express annoyed dismissal: "He can fix it himself!" (Korjatkoon sen itse!) has the he can fix in optative third-person singular (korjatkoon).
The cohortative mood is used to express plea, insistence, imploring, self-encouragement, wish, desire, intent, command, purpose or consequence. It does not exist in English, but phrases such as "let us" are often used to denote it.
The potential mood is a mood of probability, indicating that the action most likely, but not certainly, occurs. It is used in Finnish and Japanese. (In Japanese it is often called something like tentative, since potential is used to refer to a voice indicating capability to perform the action.)
In Finnish, it is mostly a literary device, as it is virtually disappeared from daily spoken language. Its suffix is -ne-, but such that any possible consonant clusters simplify, e.g. korjata -> *korjatnee -> korjannee ("probably will fix"), or tulla -> *tulnee -> tullee ("probably will come"). The auxiliary verb lie is used in other forms than the present tense as lienee, e.g. lienee korjasi "probably fixed".
The eventive mood is used in the Finnish epic poem, Kalevala. It is a combination of the potential and the conditional. It is also used in dialects of Estonian. In Finnish, there are theoretically forms like this:
- 'kävelleisin' = 'I probably would walk'
The dubitative mood is used in Ojibwa, Turkish, and other languages. It expresses the speaker's doubt or uncertainty about the event denoted by the verb.
The hypothetical mood, found in Russian, Lakota, and other languages, expresses a counterfactual but possible event or situation.