Modals to express degrees of necessity

Modals are used to express degrees of necessity and attitude toward actions. They include verbs like can, could, shall, should, will, would, may, might, must, and had better. Simple modals use the modal verb with the base form of another verb to talk about present and future necessity, while perfect modals use the modal with have and a past participle to discuss past necessity. Different modals express obligation, advice, expectation, and suggestion in both affirmative and negative forms in the present and past tense.