An article explaining the difference between the modal verbs may and might.

What is the difference between and proper use of the words may and might? I know that can refers to ability and may means permission, but I don't know where might fits into all this (although it seems to have some element of potentiality in it). I often hear people use may and might interchangeably, but it seems like may should not be used in a sentence like, it may be a good idea. Similarly, it appears maybe that might ought not to be used in a question like, might I do that? My grammatical-gut tells me there is something very different about these words and their respective uses. Help, please!


Hi Jonathan,

You are not alone in finding the modal verbs a minefield of imprecision and overlapping meanings: they represent one of the most confusing areas in grammar, both for teachers and for learners. This is because, by definition, modality deals with uncertainties and attitudes, rather than certainties and facts, and therefore it is an area of language that resists neat classification.

Also, modality – like all language in use – is evolving over time. Don’t forget that the modal verbs all started life as fully paid up lexical verbs, e.g. will meant the same as want (and still does, in some restricted senses, e.g. if you will). Not only that, modality has evolved differently in different places.

As an American (I assume) you will probably use shall even less than British English speakers, and may use must not where British speakers would say can’t, e.g. His absence must not have been noticed.

You probably don’t use would have for past probability (The person you spoke to would have been my brother). You may even use double modals (especially if you are from the South) as in I might could help you (= I might be able to help you). Modality is, in a word, a mess.

To address your specific query: You note (correctly) that can means ability and may means permission, but this is not all that they mean.

Fact number 1 about modal verbs: Each modal verb can express two kinds of meaning:

1) likelihood about situations in the world out there (sometimes called extrinsic meaning)

2) a range of meanings to do with the speaker’s internal attitudes, wishes, etc. (intrinsic meaning).

For example, the sentence Camilla may become Queen can mean both Camilla is likely to become Queen, and Camilla is allowed to become Queen. Only the context will make it clear which meaning is intended. And even the context may not be enough, as in the case (cited by some linguist, but I can’t remember who) of a person who said to a boy who was standing at the edge of an Olympic-sized swimming pool: Can you swim a length of that? (meaning: Are you able to…?) whereupon the boy jumped in (understanding: Would you mind…?). Extrinsic meaning was intended, intrinsic meaning was understood. 

Some more examples of the twin meanings of the modal verbs are:

could  possibility          It could be fun.

           ability                We could see the top.

will     predictability       It will be a nice day. 

          volition               I’ll give you a hand.

would predictability      He would say that.

           volition              Would you lend me the car?

Might is no exception to the rule that modals express two kinds of meaning. On the one hand, might in its extrinsic sense expresses what Michael Swan calls ‘weak probability’ (i.e. weaker than may). Might also expresses an intrinsic meaning, which, like may, has to do with permission. But this is much rarer than the ‘permission’ use of may, and only really survives in the rather formal question: Might I…? (as in Might I use the phone?); in some fixed phrases, such as if I might suggest... , if I might be so bold…, and in reported speech: We asked if we might take photographs. But, by far the most common use of might is in its extrinsic sense of weak probability. This contrasts with may, which is more evenly distributed (although can has largely usurped the permission function of may: Can we have a break?).

Is might interchangeable with may?

In most instances, yes (accepting that might is a little less certain than may):

It might rain                       It may rain.

You might be right             You may be right.

She might have got lost.    She may have got lost.

Might I use the phone?      May I use the phone?

However, in some cases it is not interchangeable:

1. Hypothetical statements:

If I had the time, I might learn Russian.

You might have been killed!

World War II might have lasted another two years.

(A British newspaper once headlined an article: Chernobyl: What could have happened and what might have happened. Work it out!)

2. Complaints (which are also hypothetical):

You might have phoned and said you were going to be late!

3. may not (= no permission) can’t be substituted with might not:

You may not smoke in here.

Likewise, may in the sense of 'I wish': May he rest in peace.

So, Jonathan, your hunch (that there is something different between may and might) is a reliable hunch, although the difference is more to do with the frequency and distribution of their different meanings, most of which they do in fact share. As a footnote, here is a passage from Jane Austen’s Pride and Prejudice which has a heavy concentration of modal verbs – in fact, seven of the nine ‘pure’ modals occur in the passage. What are the two that don’t?

You must give me leave to flatter myself, my dear cousin, that your refusal of my addresses is merely words of course. My reasons for believing it are briefly these: It does not appear to me that my hand is unworthy your acceptance, or that the establishment I can offer would be any other than highly desirable.

My situation in life, my connections with the family of de Bourgh, and my relationship to your own, are circumstances highly in my favour; and you should take it into further consideration, that in spite of your manifold attractions, it is by no means certain that another offer of marriage may ever be made you.

Your portion is unhappily so small that it will in all likelihood undo the effects of your loveliness and amiable qualifications. As I must therefore conclude that you are not serious in your rejection of me, I shall choose to attribute it to your wish of increasing my love by suspense, according to the usual practice of elegant females.