Some syntacticians distinguish between auxiliary verbs and light verbs. The two are similar insofar as both verb types contribute mainly just functional information to the clauses in which they appear. Hence both do not qualify as separate predicates, but rather they form part of a predicate with another expression - usually with a full verb in the case of auxiliary verbs and usually with a noun in the case of light verbs. In English, light verbs differ from auxiliary verbs in that they cannot undergo inversion and they cannot take not as a postdependent. The verbs have and do can function as auxiliary verbs or as light verbs (or as full verbs). When they are light verbs, they fail the inversion and negation diagnostics for auxiliaries, e.g. a. They had a long meeting. b. *Had they a long meeting? - Light verb had fails the inversion test. c. *They had not a long meeting. - Light verb had fails the negation test. a. She did a report on pandering politicians. b. *Did she a report on pandering politicians? - Light verb did fails the inversion test. c. *She did not a report on pandering politicians. - Light verb did fails the negation test. (In some cases, though, have may undergo auxiliary-type inversion and negation even when it is not used as an auxiliary verb – see Subject–auxiliary inversion: Inversion with other types of verb.) Sometimes the distinction between auxiliary verbs and light verbs is overlooked or confused. Certain verbs (e.g. used to, have to, etc.) may be judged as light verbs by some authors, but as auxiliaries by others. Many verbs that serve as light verbs can also serve as auxiliary verbs and/or full verbs depending on the context in which they appear. Light verbs are similar to auxiliary verbs insofar as they contribute mainly functional content (as opposed to semantic content) to the clauses in which they appear. Light verbs, however, are not auxiliary verbs, nor are they full verbs. Light verbs differ from auxiliary verbs in English insofar as they do not pass the syntactic tests that identify auxiliary verbs. The following examples illustrate that light verbs fail the inversion and negation diagnostics that identify auxiliary verbs: a. He did call Susan yesterday. b. Did he call Susan yesterday? - The auxiliary did inverts with the subject. c. He did not call Susan yesterday? - The auxiliary did can take not as a postdependent. a. He did the review of my paper yesterday. b. *Did he the review of my paper yesterday? - The light verb did cannot invert with the subject. c. *He did not the review of my paper yesterday. - The light verb did cannot take not as a postdependent. a. He has opened the window. b. Has he opened the window? - The auxiliary has inverts with the subject. c. He has not opened the window. - The auxiliary has takes not as a postdependent. a. She had a smoke. b. *Had she a smoke? - The light verb had cannot invert with the subject. c. *She had not a smoke. - The light verb had cannot take not as a postdependent. Light verbs differ from full verbs in that light verbs lack the semantic content that full verbs have. Full verbs are the core of a predicate, whereas light verbs form a predicate with another expression (often a noun) with full semantic content. This distinction is more difficult to illustrate, but it can be seen in the following examples involving reflexive pronouns: a. Jim1 took a picture of himself1. - The light verb took requires the reflexive pronoun to appear. b. *Jim1 took a picture of him1. - The light verb took prohibits the simple pronoun from appearing. a. Jim1 took a picture of himself1 to school. - The full verb took allows the reflexive pronoun to appear. b. Jim1 took a picture of him1 to school. - The full verb took allows the simple pronoun to appear. a. Sally1 gave a description of herself1. - The light verb gave requires the reflexive pronoun to appear. b. *Sally1 gave a description of her1. - The light verb gave prohibits the simple pronoun from appearing. a. Sally1 gave me a description of herself1. - The full verb gave allows the reflexive pronoun to appear b. Sally1 gave me a description of her1. - The full verb gave allows the simple pronoun to appear. The indices indicate coreference, i.e. the two coindexed words denote the same person. The reflexive pronoun must appear with the light verb, whereas the full verb allows the simple pronoun to appear as well. This distinction has to do with the extent of the predicate. The main predicate reaches down into the noun phrase when the light verb appears, whereas it excludes the noun phrase when the full verb is present.
