The verb phrase in a clause can contain two types of verb: main verbs and auxiliary verbs. If it only contains a single verb, then that is a main verb. If it contains more than one, then one will be a main verb and the other (s) auxiliary. For example:
Strange men moved about the streets in pairs.
Everything now was always reminding me of something else.
By 1646 the Royalists were defeated.
In the second example above, the auxiliary verb is used to form the tense:
Was reminding: past continuous tense.
In the last example the auxiliary is used to form the passive voice.
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