Modal auxiliary verbs are a special type of auxiliary verb, used mainly to express ability, likelihood, permission, and obligation. These include 'will', 'would', 'can', 'could', 'shall', 'should', 'may', 'might', 'must', 'ought', 'need', and 'dare'. Please do not use this tag for the non-modal auxiliaries 'be', 'have', or 'do'.
An English modal verb is a defective verb with no infinitive form, participles or personal inflections employed with a bare infinitive to express various grammatical 'moods' such as possibility, obligation, and capability. can/could, may/might, must, shall/should and will/would are the present-day English modals. Semi-modals are similarly-used verbs and verb phrases with different grammatical characteristics.