The action expressed may be physical, as in the case of such verbs as hit, play, blow and run, or it may be mental, as in think, know, imagine, believe.

Transitive and Intransitive Verbs

Action verbs may or may not take an object-a noun or pronoun that completes the action by showing who or what is affected by the action. Verbs in the following examples are transitive:

The catcher dropped the ball. [Ball is the object of dropped.]
The people believed the politician. [Politician is the object.]
The waiter ignored the customers. [Customers is the object.]

Verbs that can express action without objects are called intransitive.

The catcher shrugged.
The people chuckled.
The waiter quit.

Although some verbs are transitive only (ignore, complete) and some intransitive only (arrive, sleep), most verbs in English can be either.

EXAMPLES: The judges explained the contest rules. [transitive]
Patiently, the judges explained. [intransitive]
The contestants still misunderstood them. [transitive]
The contestants still misunderstood. [intransitive]

• NOTE Most dictionaries group the meanings of verbs according to whether they are transitive (v.t. in most dictionaries) or intransitive (v.i.). Remembering the difference will help you to find readily the meaning you want.

Linking Verbs

Some intransitive verbs help to make a statement not by expressing action, but by expressing a state or condition. These verbs link to the subject a noun, pronoun, or adjective that describes or identifies it. They are called linking verbs. The word that is linked to the subject is called a subject complement.

EXAMPLES:
The butler is the main suspect. [The subject complement suspect refers to the subject butler.]
This is he. [He refers to the subject this.]
He looks guilty. [Guilty refers to the subject he.]

The subject complement always refers to the subject of the linking verb. It may identify the subject, as in the first two examples, or describe the subject, as in the third one.
The most common linking verb is the verb be², which has the following forms: am, is, are, was, were, be, being, been (and all verb phrases ending in be, being, or been, such as can be, is being, and could have been).