Could, may and might

We use could, may and might to express degrees of possibility. Many native speakers disagree on which one expresses more or less certainty.

Compare

The restaurant may close.	It is likely that the restaurant will close.
The restaurant could close.	It is less likely that the restaurant will close.
The restaurant might close.	There is only a possibility that the restaurant will close but no one is very sure.

The speaker also shows degree of certainty or uncertainty through intonation and stress. If the speaker stresses the modal verb, they are expressing more uncertainty than if they stress the main verb.