auxiliary

auxiliary (hjelpeverb): a function word. There are two classes of auxiliary verbs: (1) grammatical auxiliaries (be, do ,have) are part of grammatical constructions, but carry little meaning. (be followed by an -ing participle marks the progressive aspect, be followed by a past participle marks the passive voice, and have followed by a past participle marks the perfective aspect.) (2) modal auxiliaries (may/might, can/could, shall/should, will/would, must, ought to) are not part of grammatical constructions, but express modal meanings. See further modality.