Main Verb (Grammar)

1. In English grammar, a main verb is any verb in a sentence that is not an auxiliary verb. Also known as a principal verb. A main verb (also known as a lexical verb or full verb) carries the meaning in a verb phrase. 
2. The verb in a main clause is sometimes identified as the main verb.

Examples

Richard Jefferies: Today through the window-pane I see a lark high up against the grey cloud, and hear his song.

Harry Crews: He shaved every morning at the water shelf on the back porch with a straight razor and always smelled of soap and whiskey.

Stephen Fry: I frankly regard corporal punishment as of no greater significance in the life of most human beings than bustles, hula-hoops, flared trousers, side-whiskers or any other fad.

Maya Angelou: The mourners on the front benches sat in a blue-serge, black-crepe-dress gloom. A funeral hymn made its way around the church tediously but successfully. It eased into the heart of every gay thought, into the care of each happy memory.

John Updike: The ball climbed on a diagonal line into the vast volume of air over center field. From my angle, behind third base, the ball seemed less an object in flight than the tip of a towering, motionless construct, like the Eiffel Tower or the Tappan Zee Bridge.

Observations

Ann Raimes: Each main verb has five forms. Three of them can be used as a complete main verb:

the -s form (present tense): she writes
the past tense form: he wrote
the simple form (present tense): they write

The other two forms do not, by themselves, indicate tense:

the -ing form: writing
the participle form ( -ed/-en form): written

They cannot be used alone as the main verb of a clause.

Edward D. Johnson: We say He assumes she is single and He assumed she was single; the secondary verb follows the main verb into the past tense, a phenomenon sometimes called the normal sequence of tenses. However, we might also say He assumed she is single. The main verb does not necessarily force its tense on the secondary verb. Often a subordinate verb that expresses something that is always true, not just true at the time of the main verb's action, is in the present tense, as in Galileo believed that the earth moves around the sun--but moved would not be wrong, and some would consider it preferable, since a subordinate clause in the present tense is slightly jarring when the main clause is in a past tense.