When to use 'could''or 'may when expressing possibility

Question

Hi,One of my students asked me for simple 'rules' on how to use 'could and 'may' to express possibility in English.Can anyone help me with these?Thanks,Petra

Daisy_J · Accepted Answer

hello,

well you can use could for either past or future tense of can, ex: "I could have done that" "I could not do it"

may is used to ask something, like "May I help you?" or "May I come to your house?"

Andriy Lapin · Answer

Greetings, Petra,

both could and may have a possibility meaning, but it is better to contrast may with can, since could in this meaning is seen only as a past form of can:

We can hope for a good performance tonight.
Her performance was the best that could be hoped for.

So, talking about can vs may distinction, it should be remembered that sentences with can can be paraphrased by it is possible + to-infinitive clause:

Even expert drivers can make mistakes. - It is possible for even expert drivers to make mistakes.

On the other hand, sentences with may expressing possibility are slightly different from those with can in that they are paraphrasable by it is possible + that-clause:

We may never succeed.- It is possible that we may never succeed.

'May' in the above sentences has the meaning of an epistemic probability (it denotes the possibility of a given proposition being or becoming true).

Finally, there is indeed one case when may and can are truly interchangeable. This case may is termed root possibility:

During the autumn, many birds can/may be observed on the rocky northern coasts of the island.

The whole sentence, however, is rather formal, and may in it sounds even more formal than can. It could be paraphrased It is possible to observe...

Perhaps this information is not simple in a sense appropriate for some students, but I still hope you will find it helpful. Ask again should you have any further questions. Please note that I did not include the description of permission (May/can I take your pen?) or other meanings of these modals, supposing that you are interested only in 'probability' aspect.

Respectfully, Gleb Chebrikoff

TrysB · Answer

Hi Petra,
Gleb has given an excellent answer to your question, but i think maybe it would be simpler to tell your students to use may only when they are asking permission--Mother, may i go to the dance tomorrow?

The words could and might should cover most expressions of possibility:

The plan could fail if we don't act quickly. The plan might fail if we don't act quickly.

In those two sentences, I think could and might are interchangeable, but in Daisy_J's sentences, there's a different shade of meaning in the possibility:

I could have done that implies that you are capable of doing whatever the 'that' refers to. But if you said, I might have done that, you are saying that there's a possibility you did the something referred to but are not sure or would rather not say.

It is well nigh impossible to construct a rule that can be applied to every situation. For me, examples seem to work best in getting the idea across rather than explanations and rules. Maybe you should have your students each make up 5 sentences as examples of using could, may and might to express possibility then read them to the class and ask for their comments on whether they think the sentences express the desired meaning. If a student says that something doesn't sound right, then you can ask them, How would you correct it?

Best wishes,
TrysB

CalifJim · Answer

AnonymousOne of my students asked me for simple 'rules' on how to use 'could and 'may' to express possibility in English.
Can anyone help me with these?The usage of 'could' and 'may' (and other modals) cannot be reduced to "simple rules". There are too many situations where these words are used, each of them slightly different.

"Possibility" is a word that can be taken in several ways. may, might, can, and could can all express possibility in one way or another. Further, they can combine with have: may have, might have, etc. And then they can be used in questions, which also changes the usage in some ways. And negations also change the usage. So the topic gets much too complex to be explained in "simple rules".

Your best bet is to find patterns and imitate them. could is more subtle than may or might, so it is more difficult for native speakers to explain it and more difficult for non-natives to master it in the meaning of "possible". It comes closer to "have the potential" in some usages.

I may/might be late to work today.
You may/might want to read this book.
Lucy may/might find this exercise too difficult.

Don't go in. It may/might/could be a trap.
We aren't finished yet. This project may/might/could still fail.
The weather is not very good today, but they say that tomorrow it may/might/could get worse.

CJ

Anonymous · Answer

Madam I want an article ab

out Possibility, I want to understand... Could you? Many thanks Masoud From Kuditan -Iraq

[ email address removed by moderator. Pleas put your contact information in your profile, not in posts ]

When to use 'could''or 'may when expressing possibility

Top answer

Get the Weekly English Kit 📬

Madam I want an article ab

out Possibility, I want to understand... Could you? Many thanks Masoud From Kuditan -Iraq

Related Questions