When we examined the structure of verb phrases, we looked at phrases that contained only one verb. This simplification let us understand the basic structure of complements like direct objects, subject complements, and so forth, without unnecessary complications, but many verb phrases are more complex, containing multiple verbs. For example, in a sentence like (1), there are two verbs, has and eaten, in the same phrase (1) Jonathan has eaten my sandwich The verb has in this sentence is a member of a subset of verbs called auxiliary verbs. The purpose of this chapter is to explore the system behind these auxiliary verbs, and particularly how these auxiliary verbs relate to the concept of tense. ------ Notes  Grammar books designed for younger students often call auxiliary verbs "helping verbs."