6: Modals of Probability

We use ‘could / may / might’ to talk about logical probability. That is, how likely or probable we think something is, depending on our knowledge. Usually, this isn’t something that we can control – we are just giving our opinion about whether we think it’s likely or not. In this case, ‘could’, ‘may’ and ‘might’ are all used to mean a medium level of probability.

Present probability

In all of these cases, I don’t know for certain if she is at home or not. But I think it’s possible that she’s at home.

·       She may be at home.

·       She might be at home.

·       She could be at home.

(Some people think that ‘could’ and ‘might’ are less likely than may, because they are considered past and so more tentative, but not everyone thinks this.)

We can also use ‘may not’ and ‘might not’. These are also both talking about a medium level of probability. We don’t use ‘could not’ like this.

·       She may not be at home. (= maybe she isn’t at home)

·       She might not be at home. (= maybe she isn’t at home)

‘May well’ suggests a strong probability.

·       She may well be at home now.

We can use the continuous infinitive to talk about things that we think are happening now.

·       She may (not) be working now

·       She might (not) be working now.

·       She could be working now.

‘May’ is not normally used for questions about probability, but can be used in negative or indirect questions. ‘Could’ and ‘might’ can be used normally in all kinds of questions.

·       NOT: may she be at home?

·       Do you think she may be at home?

·       May she not be at home?

Future probability

We can also use ‘may / may not / could / might / might not’, ‘may well’ and for the future. We often use a time expression to make it clear when we mean. We also use ‘could’ and ‘might’ for questions, rather than ‘may’ in the same way as we do when we’re talking about the present.

·       She may be at home later.

·       She might not be at home later.

·       She could be at home later.

We often prefer the continuous infinitive when we’re talking about the future. This is because there might be ambiguity (it could have two meanings). In the case of ‘may’, for example, the ambiguity is with giving permission.

·       You may go to the meeting tomorrow. (I give you permission to go.)

·       You may be going to the meeting tomorrow. (It’s likely that you are going.)

Past possibility

We use ‘may (not) / might (not) / could + have + past participle’ to talk about probability in the past. In this case, we don’t know if the things happened or not.

·       Where was Julie last night?

·       She might / may / could have been at home. (I’m not certain if she was at home or not.)

We use ‘may (not) / might (not) / could + have + past participle’ in the same way that we use the present perfect – something that maybe happened in the past that has a result in the present.

·       I tried emailing Julie but there was no answer. She might have already left.

We use ‘may (not) / might (not) / could + have + been + verb-ing’ to talk about something that maybe was in progress at another time in the past.

·       She might have been leaving when we called.

We can also use ‘may (not) / might (not) / could + have + past participle’ in the same way that we use the future perfect tense.

·       By the end of the week, she might have finished the report.

Less commonly, we can use ‘may (not) / might (not) / could + have + been + verb-ing’ in the same was that we use the future perfect continuous tense.

·       Julie could have been working all day – we should buy some dinner on the way home later.

Hypothetical probability in the past

We also talk about things that were probable or possible in the past but that didn’t happen using ‘might (not) / could + have + past participle’. This time we know it didn’t happen.

·       We might have missed the train (but we didn’t miss it).

·       We could have hurt ourselves! (But we didn’t hurt ourselves.)

Sometimes we use an expression like this to be critical.

·       Why did you do that? You might have been killed!

This is different from ‘he might have gone home’, which is normal probability in the past and where I don’t know if he went home or not. The structure of the sentence is exactly the same, so we need to understand from the context (and it’s not always clear) if the thing didn’t happen or if we don’t know.