Here's why:
* Modal Verbs: "May" is a modal verb, which expresses possibility, permission, or request. Modal verbs always work in conjunction with another verb (the main verb).
* Auxiliary Verbs: Modal verbs like "may" are auxiliary verbs, meaning they "help" the main verb to form a verb phrase.
* Verb Phrase: A verb phrase is a group of words that includes a main verb and any auxiliary verbs.
Therefore, "may have" is a modal verb phrase, not a verb phrase in itself. It needs a main verb to complete the sentence.
Example:
* "She may have left early." (Here, "have left" is the verb phrase, with "have" as the auxiliary verb and "left" as the main verb.)