Mustaqil ishlar ro’yhati

can and could

may and might

shall and should

will and would

must (no preterite; see etymology below)

Note that the preterite forms are not necessarily used to refer to past time, and in some cases, they are near-synonyms to the present forms. Note that most of these so-called preterite forms are most often used in the subjunctive mood in the present tense. The auxiliary verbs may and let are also used often in the subjunctive mood. Famous examples of these are "May The Force be with you." and "Let God bless you with good." These are both sentences that express some uncertainty; hence they are subjunctive sentences.
The verbs listed below mostly share the above features but with certain differences. They are sometimes, but not always, categorized as modal verbs.^[3] They may also be called "semi-modals".

• 
  The verb ought differs from the principal modals only in that it governs a to-infinitive rather than a bare infinitive (compare he should go with he ought to go).
  
• 
  The verbs dare and need can be used as modals, often in the negative (Dare he fight?; You dare not do that.; You need not go.), although they are more commonly found in constructions where they appear as ordinary inflected verbs (He dares to fight; You don't need to go). There is also a dialect verb, nearly obsolete but sometimes heard in Appalachia and the Deep South of the United States: darest, which means "dare not", as in "You darest do that."
  
• 
  The verb had in the expression had better behaves like a modal verb, hence had better (considered as a compound verb) is sometimes classed as a modal or semi-modal.
  
• 
  The verb used in the expression used to (do something) can behave as a modal, but is more often used with do-support than with auxiliary-verb syntax: Did she used to do it? (or Did she use to do it?) and She didn't used to do it (or She didn't use to do it)^[a] are more common than Used she to do it? and She used not (usedn't) to do it.
  

Other English auxiliaries appear in a variety of different forms and are not regarded as modal verbs. These are:

• 
  be, used as an auxiliary in passive voice and continuous aspect constructions; it follows auxiliary-verb syntax even when used as a copula, and in auxiliary-like formations such as be going to, is to and be about to;
  
• 
  have, used as an auxiliary in perfect aspect constructions, including the idiom have got (to); it is also used in have to, which has modal meaning, but here (as when denoting possession) have only rarely follows auxiliary-verb syntax (see also § Must and have to below);
  
• 
  do; see do-support.
  

For more general information about English verb inflection and auxiliary usage, see English verbs and English clause syntax. For details of the uses of the particular modals, see § Usage of specific verbs below.
Etymology[edit]
The modals can and could are from Old English can(n) and cuþ, which were respectively present and preterite forms of the verb cunnan ("to be able"). The silent l in the spelling of could results from analogy with would and should.
Similarly, may and might are from Old English mæg and meahte, respectively present and preterite forms of magan ("may, to be able"); shall and should are from sceal and sceolde, respectively present and preterite forms of sculan ("to owe, be obliged"); and will and would are from wille and wolde, respectively present and preterite forms of willan ("to wish, want").
The aforementioned Old English verbs cunnan, magan, sculan, and willan followed the preterite-present paradigm (or, in the case of willan, a similar but irregular paradigm), which explains the absence of the ending -s in the third person on the present forms can, may, shall, and will. (The original Old English forms given above were first and third person singular forms; their descendant forms became generalized to all persons and numbers.)
The verb must comes from Old English moste, part of the verb motan ("to be able to, be obliged to"). This was another preterite-present verb, of which moste was in fact the preterite (the present form mot gave rise to mote, which was used as a modal verb in Early Modern English; but must has now lost its past connotations and has replaced mote). Similarly, ought was originally a past form—it derives from ahte, preterite of agan ("to own"), another Old English preterite-present verb, whose present tense form ah has also given the modern (regular) verb owe (and ought was formerly used as a past tense of owe).
The verb dare also originates from a preterite-present verb, durran ("to dare"), specifically its present tense dear(r), although in its non-modal uses in Modern English it is conjugated regularly. However, need comes from the regular Old English verb neodian (meaning "to be necessary")—the alternative third person form need (in place of needs), which has become the norm in modal uses, became common in the 16th century.^[8]
Syntax[edit]
A modal verb serves as an auxiliary to another verb, which appears in the infinitive form (the bare infinitive, or the to-infinitive in the cases of ought and used as discussed above). Examples: You must escape; This may be difficult.
The verb governed by the modal may be another auxiliary (necessarily one that can appear in infinitive form—this includes be and have, but not another modal, except in the non-standard cases described below under § Double modals). Hence a modal may introduce a chain (technically catena) of verb forms, in which the other auxiliaries express properties such as aspect and voice, as in He must have been given a new job.
Modals can appear in tag questions and other elliptical sentences without the governed verb being expressed: ...can he?; I mustn't.; Would they?
Like other auxiliaries, modal verbs are negated by the addition of the word not after them. (The modification of meaning may not always correspond to simple negation, as in the case of must not.) The modal word can combine with not forms the single word cannot. Most of the modals have contracted negated forms in n't which are commonly used in informal English: can't, mustn't, won't (from will), etc.
Again like other auxiliaries, modal verbs undergo inversion with their subject, in forming questions and in the other cases described in the article on subject–auxiliary inversion: Could you do this?; On no account may you enter. When there is negation, the contraction with n't may undergo inversion as an auxiliary in its own right: Why can't I come in? (or: Why can I not come in?).
More information on these topics can be found at English clause syntax.
Past forms[edit]
The preterite (past) forms given above (could, might, should, and would, corresponding to can, may, shall, and will, respectively) do not always simply modify the meaning of the modal to give it past time reference. The only one regularly used as an ordinary past tense is could, when referring to ability: I could swim may serve as a past form of I can swim.
All the preterites are used as past equivalents for the corresponding present modals in indirect speech and similar clauses requiring the rules of sequence of tenses to be applied. For example, in 1960, it might have been said that People think that we will all be driving hovercars by the year 2000, whereas at a later date it might be reported that In 1960, people thought we would all be driving hovercars by the year 2000.
This "future-in-the-past" (also known as the past prospective, see: prospective) usage of would can also occur in independent sentences: I moved to Green Gables in 1930; I would live there for the next ten years.
In many cases, in order to give modals past reference, they are used together with a "perfect infinitive", namely the auxiliary have and a past participle, as in I should have asked her; You may have seen me. Sometimes these expressions are limited in meaning; for example, must have can refer only to certainty, whereas past obligation is expressed by an alternative phrase such as had to (see § Replacements for defective forms below).