¤ Finite & Non-finite Verbs ←[pdf]

¤ Auxiliary Verbs ⇐ «Auxiliaries are required with non-finite verbs. This is their role to mark non-finite verb forms for tense, aspect and voice, which non-finite verbs cannot express. Finite verbs mark these features on their own.»

(Bernard T. O’Dwyer, Modern English Structures: Form, Function)

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