5. Synonyms and Substitutes

Some modal verbs are synonyms and can be used instead of each other. For example, SHOULD, OUGHT TO are close synonyms; WILL, WOULD are synonyms in some polite requests. It is sometimes difficult for language learners to choose the right synonym. Always choose a more general synonym out of a group of synonyms or a synonym with a more straightforward meaning. For example, MAY, MIGHT, COULD are synonyms in the meaning "possibility". MAY has two other meanings, COULD has four other meanings, and two of them are pretty difficult to distinguish from "possibility" without a clear context. Only MIGHT has just one meaning: possibility. The choice should be obvious – use MIGHT or MAY for "possibility". Recommendations which of the synonyms to use are given in the materials on specific modal verbs.

Modal verbs are very common and widely used in speech and writing. Still, there are quite a few substitutes for modal verbs. They are the phrases "be able to, have to, have got to, be to, be supposed to, be going to, used to", the adverbs "probably, maybe", and some others. Some substitutes are also very common and widely used, for example, HAVE TO instead of MUST in the meaning "strong necessity"; PROBABLY instead of MUST in the meaning "strong probability"; MAYBE instead of MAY, MIGHT, COULD in the meaning "possibility".

The most important use of substitute phrases is in those cases where modal verbs can't be used. For example, the modal verb MUST in the meaning "strong necessity" doesn't have the past form, so the substitute phrase HAVE TO (necessity) is typically used instead of the modal verb MUST in the past tense, with a little change in meaning.

Maria must go to the bank today. (strong necessity)

She has to go to the bank today. (necessity)

She had to go to the bank yesterday. (necessity; realized action)

Substitute phrases are described together with the modal verbs they substitute for in the materials on specific modal verbs.