A verb phrase consists of a main verb and any auxiliaries that modify it, which act together within a sentence as a single unit. The main verb is typically the word that indicates the action or state of being that is expressed, such as "run," "jump," or "is." Auxiliary verbs within a sentence come before the main verb and are usually presented directly in front of it, though they may be broken up to form questions or to include negating words. A verb phrase is often identified as a single unit within the sentence, which needs to be replaced in its entirety by another word or phrase if someone wants to make a change.
The simplest type of verb phrase found in a sentence is typically a single word, which is the main verb in it. For example, in the sentence "I wrote a letter," the word "wrote" is a verb and acts as a single-word verb phrase within it. There are no auxiliary verbs that modify it and so it can be replaced by other words or phrases to change the meaning of the sentence. Examples of this are sentences like "I ate a letter" or "I burned a letter" in which new verbs are used.
Auxiliary verbs are typically used in a more complex verb phrase, often to express tense or modality within a sentence. Tense is usually provided by the auxiliaries "do," "be," and "have" such as "I have showered already today" or "He is going outside" where "have" and "is" are used as auxiliaries. There are also auxiliaries of modality such as "will" in "I will go outside" or "should" in "He should shower tonight." These auxiliary and main verbs are joined together to form the verb phrase such as "is going" or "should shower."
It is important to recognize verb phrases within a sentence since the entire thing needs to be treated as a single unit. For example, in the sentence "I should have been walking to the store," the sentence consists of a subject and a predicate that consists of both verb and prepositional phrases. The subject is "I" and the verb phrase is "should have been walking," while "to the store" is a prepositional phrase.
In order for a new verb to be used in this sentence, it has to replace the entire phrase, or another phrase can be used. Without considering the entire verb phrase, the sentence can become something like "I should have been walked to the store," which is grammatically awkward or incorrect. Inappropriate auxiliaries remained in the sentence while the main verb alone was replaced. Instead, the entire phrase needs to be changed to something like "I walked to the store," or "I should have walked to the store."