Auxiliaries

Auxiliaries, in linguistics, are a class of verbs that accompany a main verb to express grammatical information such as tense, aspect, mood, voice, or modality. They form periphrastic constructions rather than changing by inflection alone.

Two broad groups exist: primary auxiliaries (be, have, do) and modal auxiliaries (can, could, may, might, shall, should, will, would, must, need, ought). Primary auxiliaries help form different aspects and tenses; modal auxiliaries express possibility, necessity, obligation, or permission.

Syntax and usage: Auxiliaries typically precede the main verb and participate in inversion for questions. Negation is built with not following the auxiliary; in English, when there is no auxiliary of its own, do-support is used (Do you know?).

Common functions include be + -ing for progressive aspect (They are studying); have + past participle for perfect aspect (She has finished); be + past participle for passive voice (The ball was thrown). Modals express modality (may arrive, must leave).

Some languages employ semi-auxiliaries or rely on particles rather than full verbs; cross-linguistic systems vary in how many auxiliary layers exist and how they interact with main verbs. Historically, auxiliary verbs often originate from full verbs and can shed independent semantic load, becoming purely grammatical markers.