• Dummy Operator
• Modal
• NICE Properties
• Notes on "Do"
• Notes on Verbs
• Using Correct Forms of the Verb "Be"

Examples and Observations:

• "In one of their uses, the primary verbs precede a main, lexical verb. When used in this way, they may be said to be functioning as auxiliary verbs within the clause. This is illustrated in (17):

  (17a) He is speaking to her now.
  (17b) I have visited my grandmother every Christmas since I was a child.
  (17c) You didn't eat your lunch.

  In simple terms, auxiliary verbs are 'additional' verbs (or 'helping' verbs, as EFL teachers often say). In Modern English, primary be is used as an auxiliary in either the progressive construction, illustrated in (17a), or in the passive construction, illustrated in (18):

  (18) She was spoken to yesterday.

  When used as an auxiliary, have appears in perfect constructions, as shown in (19):

  (19a) He has spoken to her.
  (19b) He had spoken to her yesterday.

  When used as an auxiliary, do appears in negative and interrogative constructions:

  (20a) I didn't speak to her yesterday.
  (20b) Did you speak to her yesterday?

  Notice that it is the job of the primary verb to carry the tenseinflection for the entire verb phrase (VP), while the main verb conveys the semantic content."
  (Martin J. Endley, Linguistic Perspectives on English Grammar: A Guide for EFL Teachers. Information Age Publishing, 2010)

• "Primary and modal verbs do not follow the same grammatical rules. In particular:

  - Primaries have -s forms; modals do not:
  is, has, does . . .
  - Primaries have nonfinite forms; modals do not:
  to be, being, been"

  (David Crystal, Rediscover Grammar, 3rd ed. Pearson Longman, 2003)
• Be as Auxiliary of the Progressive and of the Passive
  "[I]n a sense we can answer the question of how many primary auxiliaries there are with either four or three; the verb be does double duty as the auxiliary of the progressive and the auxiliary of the passive. Since these are quite different functions, and since it is quite easy to distinguish them, it is best to view them as two different primary auxiliaries which have the same form. It is easy to distinguish the two uses. First of all, the progressive be and the passive be are followed by different forms of the verb, ing form (be eating) and ppart (be eaten), respectively. Second, passive sentences have some particular characteristics: for instance, in a passive sentence you can usually have a by phrase (be eaten by a shark)."
  (Kersti Börjars and Kate Burridge, Introducing English Grammar, 2nd ed. Hodder, 2010)

• Functions of Do
  "We often use the verb do as a stand-in auxiliary, much in the same way as we use primary and modal auxiliaries. Like primary verbs, it can function as an auxiliary or as a principal verb because it has a full verb inflectional paradigm.
  
  "Do as an auxiliary verb:

  a. 'This! Why, father, what do you mean? This is home! [Porter]
  b. 'Does everybody at the academy dress like that?' [Gogol]

  Do as a lexical verb:

  a. 'But that the most acceptable service of God is doing good to man.' [Franklin]
  b. 'Sane people did what their neighbors did, so that if any lunatics were at large, one might know and avoid them.' [Eliot]
  c. 'The thick-iron ferrule is worn down, so it is evident that he has done a great amount of walking with it.' [Doyle]

  Because of the flexibility of this verb (it is also used to form questions, negatives, and for emphasis), it is important to pay close attention to how it is used. When it is used as an auxiliary, like the primary and modal verbs, it will occupy the initial position in the verb phrase, and there will always be a non-finite lexical verb to follow. When it is used as a lexical verb, it may be preceded by an auxiliary verb or simply stand alone."
  (Bernard O'Dwyer, Modern English Structures: Form, Function, and Position. Broadview Press, 2000)