Additional forms can thus be supplied: the infinitive (to) be able to, the subjunctive and (rarely) imperative be able to, and the participles being able to and been able to. The modals may and might, in their meanings expressing permission, can be replaced by am/is/are allowed to and was/were allowed to. The modal must in most meanings can be replaced by have/has to. This supplies the past and past participle form had to, and other forms (to) have to, having to. Will can be replaced by am/is/are going to. This can supply the past and other forms: was/were going to, (to) be going to, being/been going to. The modals should and ought to might be replaced by am/is/are supposed to, thus supplying the forms was/were supposed to, (to) be supposed to, being/been supposed to. Contractions and reduced pronunciation As already mentioned, most of the modals in combination with not form commonly used contractions: can't, won't, etc. Some of the modals also have contracted forms themselves: The verb will is often contracted to 'll; the same contraction may also represent shall. The verb would (or should, when used as a first-person equivalent of would) is often contracted to d. The had of had better is also often contracted to d. (The same contraction is also used for other cases of had as an auxiliary.) Certain of the modals generally have a weak pronunciation when they are not stressed or otherwise prominent; for example, can is usually pronounced . The same applies to certain words following modals, particularly auxiliary have: a combination like should have is normally reduced to or just "shoulda". Also ought to can become "oughta". See weak and strong forms in English. Usage of specific verbs Can and could The modal verb can expresses possibility in a dynamic, deontic, or epistemic sense, that is, in terms of innate ability, permissibility, or possible circumstance. For example: I can speak English means "I am able to speak English" or "I know how to speak English." You can smoke here means "you may (are permitted to) smoke here" (in formal English may or might is sometimes considered more correct than can or could in these senses). There can be strong rivalry between siblings means that such rivalry is possible. The preterite form could is used as the past tense or conditional form of can in the above meanings (see above). It is