fromEnglish Grammar Today
We usecould, mayandmightto express degrees of possibility. Many native speakers disagree on which one expresses more or less certainty.
Compare
| It is likely that the restaurant will close. |
| It is less likely that the restaurant will 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 andstress. If the speaker stresses the modal verb, they are expressing more uncertainty than if they stress the main verb.