If you want to talk about how possible something is you can use Modal Verbs of Possibility.

Let’s say, for example, that you are 100% certain that you are going to win:

I will win a million dollars if I put everything on red!

Chances are though you will lose. Being more cautious you could say:

I may win a million dollars if I put everything on red…

So you use the modal verb may to show that something is possible but by no means certain.

Modal Verbs

These are the different verbs we use to talk about possibility:

will, may, might, would, could, can

Degrees of Possibility

And here’s how we use them. Remember that there are a lot of overlapping areas and while one person could use might, another could use may. People don’t always agree on the degree of possibility so there’s often more than one choice to be made.

far removed possibility (imagining things)

That would be awesome!

I wouldn’t dream of it!

Often these are for flights of fancy; imagine yourself shivering outside in the rain while you’re waiting for a bus. You might turn to your friend and say:

Wouldn’t it be nice to be lying on a beach in Cuba now?

And then a car passes and splashes water over you.

real possibility

Here you’re talking about something which could happen. It’s a genuine possibility.

It can get very tense in some of these meetings.

The Cowboys may win but with their quarterback injured I’m not so sure…

Here may shows a lesser degree of possibility compared to can.

certainty (based on logical assumptions)

Ok, now we’re on firmer ground. Based on your knowledge of the real world and barring any unforeseen accidents, these things are going to happen.

He will be in Rome by now.

He must be in Rome by now.

Sometimes must is used to show a slight surprise. You were expecting him to call you when he reached Rome but he hasn’t so you’re wondering allowed why he has not.

degrees of possibility (in the present and future)

These are commonly the three degrees of possibility:

He may be upstairs.

It’s likely, in other words.

He might be upstairs.

It’s less likely; I’m not so sure.

He could be upstairs.

I really don’t know and I’m speculating now.

unlikely, impossible or illogical

These speak for themselves. We’re talking about events which have surprised us or which we don’t believe.

He couldn’t have got lost.

He can’t have got lost.

It can’t be raining!

He wouldn’t still be at work, would he?

prediction

Here we’re predicting. How certain we are is open to debate. Are you a betting person?

She will win.

Certainty there.

She may win.

She might win.

She could win.

And then slightly less certain as we move down the list.

suggestions in the future

Finally an easy one:

We could go to the cinema.

A possibility here.

Useful Links

Modal Verbs‏‎ in English – an overview of different kinds of modals

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