Modal verbs

Can: Expresses ability, permission, or possibility.

Example: I can swim. (ability)

Example: You can go now. (permission)

Could: Expresses past ability, polite requests, or possibility.

Example: When I was younger, I could run fast. (past ability)

Example: Could you pass the salt? (polite request)

May: Expresses permission or possibility.

Example: You may leave the room. (permission)

Example: It may rain today. (possibility)

Might: Expresses possibility, usually weaker than "may".

Example: She might come to the party. (possibility)

Must: Expresses necessity, strong obligation, or deduction.

Example: You must wear a seatbelt. (necessity)

Example: He must be tired after such a long trip. (deduction)

Shall: Expresses future actions or offers, often formal.

Example: I shall return by evening. (future action)

Example: Shall we dance? (offer)

Could: Expresses advice, recommendation, or expectation.

Example: You should study for the exam. (advice)

Example: She should be here by now. (expectation)

Will: Expresses future actions or willingness.

Example: I will call you tomorrow. (future action)

Example: Will you help me with this? (willingness)

Would: Expresses polite requests, offers, or hypothetical situations.

Example: Would you like some tea? (offer)

Example: If I were you, I would apologize. (hypothetical situation)

Ought to: Expresses advice or moral obligation, similar to "should".

Example: You ought to apologize to her. (advice).