These auxiliaries affect the mood of the verb; that is, they determine whether a verb is a fact, desire, possiblity, or command. They are most commonly used to represent degrees of freedom or severity.
Most common modal auxiliaries:
will, shall, can, may, need (to), dare, would, should, could, might, must, ought (to)
Ability: I can run.Necessity: I must run.Obligation: I ought to run.Permission: I may run.
Defective Modal Auxiliaries
- usually only exist in the Present and Past (or only in ONE Tense)
- have no infinitives (no: to can!)
- have no direct objects (I can do it not: I can it)
- do not have an -s in the third person singular: he can (Present Tense)
- simply use NOT as a negation: he may not, he cannot (spelling!)
- there is no TO between the auxiliary and the full verb: he can come
Simple Present Simple Past Substitute I can I could to be able to I may I might to be allowed / permitted to I shall I should to be to I will I would to want / wish / desire / intend to I must ------------ to have to / to be obliged to / to be forced to / to be compelled to ---------- I ought to ------------- I used to I would / to be in the habit of (doing s.th.) I dare* ----------- to dare to I need ---------- to need to
*(The Guardian, Friday February 28, 2003: The glory that is Brum
How dare Birmingham, a city chiefly known for spawning Ozzy Osbourne and a laughably adenoidal accent, presume to join a list of truly great cities such as Paris, Florence and Amsterdam as a European City of Culture? )