Modern standard English has various verb forms, including: They can be used to express tense (time reference), aspect, mood, modality and voice, in various configurations.
As in many other languages, the means English uses for expressing the three categories of tense (time reference), aspect and mood are somewhat conflated (see tense–aspect–mood).
The tenses, aspects and moods that may be identified in English are described below (although the terminology used differs significantly between authors).
In common usage, particularly in English language teaching, particular tense–aspect–mood combinations such as "present progressive" and "conditional perfect" are often referred to simply as "tenses".
Verb tenses are inflectional forms which can be used to express that something occurs in the past, present, or future.
[1] In English, the only tenses are past and non-past, though the term "future" is sometimes applied to periphrastic constructions involving modals such as will and go.
For certain grammatical contexts where the present tense is the standard way to refer to the future, see conditional sentences and dependent clauses below.
The morphological present tense can be used to refer to future times, particularly in conditional sentences and dependent clauses.
"Simple" forms of verbs are those appearing in constructions not marked for either progressive or perfect aspect (I go, I don't go, I went, I will go, etc., but not I'm going or I have gone).
They may also denote a temporary state (imperfective aspect), in the case of stative verbs that do not use progressive forms (see below).
By using non-finite forms of the auxiliary have, perfect aspect can also be marked on infinitives (as in should have left and expect to have finished working), and on participles and gerunds (as in having seen the doctor).
Indicative mood, in English, refers to finite verb forms that are not marked as subjunctive and are neither imperatives nor conditionals.
When they are used to make requests, the word please (or other linguistic device) is often added for politeness: First person imperatives (cohortatives) can be formed with let us (usually contracted to let's), as in "Let's go".
To form the passive voice (where the subject denotes the undergoer, or patient, of the action), a periphrastic construction is used.
Passive voice can be expressed in combination together with tenses, aspects and moods, by means of appropriate marking of the auxiliary (which for this purpose is not a stative verb, i.e. it has progressive forms available).
In most questions (and other situations requiring inversion), when negated, and in certain emphatic statements, a periphrastic construction consisting of did and the bare infinitive of the main verb is generally used instead—see do-support.
Typical examples include telling jokes (as in Three men walk into a bar), emotional storytelling (as in So I come home and I see this giant box in front of my door) and referring to historical events (as in King Henry wins his last victory in 1422.).
If the verb in question does not use the progressive aspect, then the plain past perfect is used instead (see examples in the previous section).
It thus refers to an action or event conceived of as having limited duration, taking place at the present time.
This often contrasts with the simple present, which expresses repeated or habitual action (We cook dinner every day).
The choice of present perfect or past tense depends on the frame of reference (period or point in time) in which the event is conceived as occurring.
For example: I wrote a letter this morning (it is now afternoon); He produced ten plays (he is now dead or his career is considered over, or a particular past time period is being referred to); They never traveled abroad (similarly).
For example, This implies that I still live in Paris, that he still holds the record and that we still eat together every morning (although the first sentence may also refer to some unspecified past period of five years).
(A sentence without perfect aspect, such as I am sitting here for three hours, implies an intention to perform the action for that length of time.)
There is also a going-to future, common in colloquial English, which is often used to express intentions or predictions (I am going to write a book some day; I think that it is going to rain).
The auxiliary verbs could and might can also be used to indicate the conditional mood, as in the following: Forms with would may also have "future-in-the-past" meaning: See also § Indirect speech and § Dependent clauses.
This commonly occurs in content clauses (typically that-clauses and indirect questions), when governed by a predicate of saying (thinking, knowing, etc.)
Other modifiers may be placed between to and the verb (as in to boldly go; to slowly drift away), but this is sometimes regarded by some as a grammatical or stylistic error – see split infinitive for details.
In a passive use, an object or preposition complement becomes zero, the gap being understood to be filled by the noun phrase the participle modifies (compare similar uses of the to-infinitive above).
[24] Besides its nonfinite verbal uses as a gerund or present participle, the -ing form of a verb is also used as a deverbal noun, denoting an activity or occurrence in general, or a specific action or event (or sometimes a more distant meaning, such as building or piping denoting an object or system of objects).