Modal Verbs in English Grammar

Possibility

• Modal verbs used to express possibility: can, could, may, might
• Expressing ability or capacity: can (e.g., "I can speak French")
• Expressing uncertainty or doubt: could, may, might (e.g., "It could be raining", "She may be late", "It might be true")
• Degrees of possibility:
  • can (high probability)
  • could (possible but not certain)
  • may (possible but not very likely)
  • might (low probability)

Necessity

• Modal verbs used to express necessity: must, have to, need to
• Expressing obligation or requirement: must, have to (e.g., "You must try this", "I have to finish this project")
• Expressing lack or requirement: need to (e.g., "I need to study for the exam")

Obligation

• Modal verbs used to express obligation: must, have to, should
• Expressing strong obligation: must (e.g., "You must attend the meeting")
• Expressing mild obligation: should (e.g., "You should try to arrive on time")
• Expressing obligation or duty: have to (e.g., "I have to help my friend")

Permission

• Modal verbs used to express permission: can, may, could
• Expressing permission or allowance: can, may (e.g., "You can go to the party", "You may enter the room")
• Expressing permission or possibility: could (e.g., "You could go to the movies if you want")

Probability

• Modal verbs used to express probability: will, would, may, might, could
• Expressing high probability: will (e.g., "It will probably rain tomorrow")
• Expressing uncertainty or doubt: would, may, might, could (e.g., "It would be nice if it didn't rain", "It may rain tomorrow", "It might rain tomorrow", "It could rain tomorrow")

Advice

• Modal verbs used to express advice: should, ought to, had better
• Expressing strong advice: should (e.g., "You should take a break")
• Expressing mild advice: ought to (e.g., "You ought to try this new restaurant")
• Expressing strong warning or recommendation: had better (e.g., "You had better hurry up or you'll be late")