The verb phrase consists exclusively of verbs. In most verb phrases, one verb, called the main verb, carries information about what kind of event, activity, state, etc. the verb phrase refers to. Other verbs in the verb phrase, called auxiliary verbs, contribute additional perspectives on the meaning of the verb phrase, relating, for example, to time and modality (possibility, necessity, volition, prediction). The following example illustrates the structure of a typical verb phrase.
The main verb is the head of the verb phrase, just as a noun or pronoun is the head of a noun phrase.
In a verb phrase with more than one verb, the main verb always comes last.
In verb phrases that are marked for tense (present or past) the tense inflection is always attached to the first verb in the verb phrase. In the example above, the first auxiliary could is a past tense form (can would be the present tense form).
Not all verb phrases are marked for tense, however. Those that contain no present or past tense verb forms are referred to as non-finite verb phrases. Examples include infinitival verb phrases, and verb phrases introduced by present or past participles (-ing and -ed forms). The following clauses all start with a non-finite verb phrase.
(1) To guarantee maximum security all user keys must be safely stored.
(2) Having established peace throughout the region, the army returned to Rome.
(3) Blinded by his misunderstanding of the data, Professor Jones refused to change his attitude towards more recent theories.