• Predicator
• Notes on Verbs
• Primary Verbs
• Ten Quick Questions and Answers About Verbs and Verbals in English

Examples (definitions #1 and #2):

• Sheila sells seashells.
• Sheila has sold seashells by the seashore.
• Tomorrow Sheila will sell seashells by the seashore.
• "Today through the window-pane I see a lark high up against the grey cloud, and hear his song."
  (Richard Jefferies, "Hours of Spring," 1886)
• "He shaved every morning at the water shelf on the back porch with a straight razor and always smelled of soap and whiskey."
  (Harry Crews, A Childhood: The Biography of a Place. Harper & Row, 1978)
• "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."
  (Stephen Fry, Moab Is My Washpot. Soho Press, 1997)
• "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."
  (Maya Angelou, I Know Why the Caged Bird Sings. Random House, 1970)

• "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."
  (John Updike, "Hub Fans Bid Kid Adieu," 1960)

Observations:

• "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."
  (Ann Raimes, How English Works: A Grammar Handbook With Readings. Cambridge Univ. Press, 1998)
• Main Verbs in Verb Phrases
  "A verb phrase is the helping verb plus the main verb. The final word in a verb phrase, the main verb, carries the primary meaning of the verb phrase. Sometimes more than one helping verb accompanies the main verb. In the following sentences, the verb phrases are bold; HV appears [after] each helping verb, and MV appears [after] each main verb.

  He is[HV] biking[MV] to Vermont from Boston.
  
  They will[HV] arrive[MV] in time for the game.
  
  Cy Young has[HV] always been[HV] considered[MV] one of the best pitchers in baseball history.

  Notice that sometimes words not part of the verb phrase come between the helping verb and the main verb.
  
  "Typical helping verbs include: be, being, been, is, am, are, was, were, do, did, does, has, have, had, must, may, can, shall, will, might, could, would, should."
  (The New York Times Guide to Essential Knowledge, 2nd ed. St. Martin's Press, 2007)
• Be, Have, and Do as Main Verbs
  "Several verbs, such as be, have, and do, have a variety of syntactic and lexical functions: They can be main or auxiliary verbs.
  
  "John is a student, and he does his homework daily [be and do are main lexical verbs], Bob has been working on his term paper [work is the main lexical verb, and has and been are auxiliary].
  
  " . . . Every English sentence needs to have a verb to be grammatical. However, only the main verb is absolutely essential."
  (Eli Hinkel, Teaching Academic ESL Writing: Practical Techniques in Vocabulary and Grammar. Lawrence Erlbaum, 2004)
• Relative Time
  "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."
  (Edward D. Johnson, The Handbook of Good English. Washington Square Press, 1991)