ken to. 'Can' or 'could' can be used instead, although formal American English prefers 'may'. In both cases the preterite form is viewed as more hesitant or polite.and couldnegation of can is the single word "cannot", occasionally written as two words "can not" or the contraction "can't". The negation of could is "could not", or "couldn't". Is used to express ability. "I can speak English" means "I am able to speak English", or "I know how to speak English". Is also used to express that some state of affairs is possible, without referring to the ability of a person to do something: "There can be a very strong rivalry between siblings" can have the same meaning as "There is sometimes a very strong rivalry between siblings". and can't can be used to express beliefs about situations: " He cannot have left already; why would he want to get there so early? "expresses with less certainty the same proposition as" He has not left already "does.can and could can be used to make requests:" Can you pass me the cheese? means "Please pass me the cheese". Could can be used in the same way, and might be considered more polite.modalstandard English usage, it is rare to use more than one modal verb consecutively, with a few exceptions such as might have to or may have used to. A greater variety of double modals appears colloquially in some regional or archaic dialects. In Southern American English, for example, phrases such as might could or ought to should are sometimes used in conversation. The double modal may sometimes be redundant, as in "I ought to should do something about it", where ought to and should are synonymous and either one could be removed from the sentence. In other double modals, the two modal verbs convey different meanings, such as "I might could do something about it tomorrow", where might indicates the possibility of doing something and could indicates the ability to do it.modals also occur in the closely related Germanic language Scots.example of the double modal used to could can be heard in country singer Bill Carlisle's 1951 song "Too Old to Cut the Mustard": used to could jump just like a deer, now I need a new landing gear. used to could jump a picket fence, now I'm lucky if I jump an inch.kinds of double modal phrases are generally not regarded as correct grammar, although other double modals may be used instead. "I might could do something about it" is more often expressed as "I might be able to do something about it", which is considered more grammatical. Similarly used to could is usually expressed as used to be able to. Double modals can also be avoided by replacing one of the modal verbs with an appropriate adverb, such as using probably could or might possibly in place of might could.
1.3 Main Types of Modal Verbs in the English Language
modal verbs are grouped according to...
