1. Which are?
1.1. Can
1.2. Could
1.3. May
1.4. Migth
2. Uses
2.1. Ability
2.1.1. Present or Future
2.1.1.1. Can
2.1.1.1.1. ability in the present or future
2.1.2. Past
2.1.2.1. could
2.1.2.1.1. could/ might have + past participle
2.1.2.1.2. couldn’t have + past participle + comparative adjective
2.2. Possibility, deduction and speculation
2.2.1. Present
2.2.1.1. Can
2.2.1.1.1. things which are generally possible
2.2.1.2. may, might and could
2.2.1.2.1. specific possibilities
2.2.1.2.2. similar to ’perhaps’ or ’maybe’:
2.2.1.2.3. well after
2.2.1.3. We use the same forms when we are making a deduction based on evidence or on our experience:
2.2.2. Past
2.2.2.1. Could
2.2.2.1.1. general possibility in the past
2.2.2.2. could/might
2.2.2.2.1. a specific past possibility
2.2.2.3. might have
2.2.2.3.1. past opportunity which we know was not taken
2.2.2.4. can’t have / couldn’t have:
2.2.2.4.1. negative deduction
2.2.2.4.2. express surprise or disbelief
2.2.3. Future
2.2.3.1. will / won’t be able to
2.2.3.1.1. certain that something will be possible or impossible
2.2.3.2. may, might or could.
2.2.3.2.1. predictions which are less certain
2.2.3.2.2. Could usually describes a weaker possibility
2.2.3.3. may/might have + past participle
2.2.3.3.1. possible completed action
2.3. Arrangements
2.3.1. can could or be able to
2.4. Suggestions, offers, and requests
2.5. Asking for and giving/Refusing permission
2.5.1. Present/Future
2.5.1.1. can/can‘t
2.5.1.1.1. permission granted or refused by the person being asked and for permission subject to some external authority such as the law:
2.5.2. Past
2.5.2.1. could/couldn’t
2.5.2.1.1. general permission