Definition of Semi-Auxiliaries and Semi-Modals

Glossary of Grammatical and Rhetorical Terms

semi-auxiliaries (semi-modals)
Examples of semi-auxiliaries (or semi-modals) in English grammar. (Getty Images)

In English grammar, a semi-auxiliary is a multi-word construction based on an auxiliary verb and having some of the same grammatical characteristics. Also known as a semi-modal or a lexical auxiliary.

Semi-auxiliaries include be about to, be able to, be going to, be likely to, be supposed to, had better, have to, ought to, used to, and would rather. Some are followed by an infinitive; others by a zero infinitive.

Geoffrey Leech et al. note that the semi-modals "are probably the most cited cases of grammaticalization in the ongoing history of English. Among these, in turn, the protoypical, most indubitable cases of semi-modal status are BE going and HAVE to . . .. [T]he lexically independent verbs have and go have, over the centuries, gradually acquired an auxiliary-like function in construction with the infinitive to" (Change in Contemporary English: A Grammatical Study, 2012).

Also Known As: semi-modal, quasi-modal, periphrastic modal, phrasal auxiliary, modal-like, modal idiom, lexical auxiliary

Examples and Observations

  • "What you have become is the price you paid to get what you used to want."
    (Mignon McLaughlin, The Complete Neurotic's Notebook. Castle Books, 1981)
  • "Women have got to make the world safe for men since men have made it so darned unsafe for women."
    (Lady Nancy Astor)
  • "We had better dispense with the personification of evil, because it leads, all too easily, to the most dangerous kind of war: religious war."
    (Konrad Lorenz, On Aggression, 1963)
  • "Girl, you look so good, someone ought to put you on a plate and sop you up with a biscuit."
    (Arsenio Hall as Reverend Brown in Coming to America, 1988)
  • "Reckon somebody oughta help the poor guy."
    (Nigel in Finding Nemo, 2003)
  • "A great teacher is supposed to show them there are other points of view besides their own."
    (Matthew Morrison as Will Schuester, "The Substitute." Glee, 2010)
  • "I'm shaking the dust of this crummy little town off my feet and I'm going to see the world. Italy, Greece, the Parthenon, the Coliseum. Then I'm going to go to college and see what they know, and then I'm going to build things. I'm gonna build air fields. I'm gonna build skyscrapers a hundred stories high. I'm gonna build bridges a mile long."
    (George Bailey in It's a Wonderful Life [1946], adapted from the short story "The Greatest Gift" [1943] by Philip Van Doren Stern)

Strings of Semi-Auxiliaries

"Only the first word in a semi-auxiliary is a true auxiliary, since only that word functions as an operator, for example in forming questions:

Is Sandra going to apply for the job?
Had I better eat now?
Is Jennifer supposed to phone us today?

The semi-auxiliaries may come together to make a long string of verbs:

We seem to be going to have to keep on paying the full fee.
They are likely to be about to start working on our project.

(Sidney Greenbaum and Gerald Nelson, An Introduction to English Grammar, 3rd ed. Pearson, 2009)

The Habitual Past With Used to

"The  past form of habitual aspect is often expressed by the semi-auxiliary used to:

Your mother used to sleep like a log.
People used to whitewash their ceilings.
My father used to bath us six kids in front of the fire.

These utterances describe situations that occurred habitually in the past."
(Thomas Edward Payne, Understanding English Grammar: A Linguistic Introduction. Cambridge University Press, 2010)

The Future With Going to

"The salient semantic and pragmatic features of going to which are generally underlined by grammarians are:

- its relatively informal style with respect to will (Huddleston and Pullum, 2002: 211). The widespread use of gonna (as opposed to going to in conversation is often a marker of informality; and it certainly is in written texts when spelt that way. . . .;
- its dual meaning of 'future fulfillment of present intention' and 'future result of present cause' (Quirk et al. 1985), which have often been summed up as its intentional meaning and its predictive meaning;
- its tendency to be used to indicate the proximity of a future event unless there is a time adverbial or context indicating otherwise (Declerck 1991: 114). The fact that the structure is that of the present progressive form of the verb to go would seem to underline strongly its connection with the present (Williams 2002: 102)."

(Yiva Berglund and Christopher Williams, "The Semantic Properties of Going to: Distribution Patterns in Four Subcorpora of the British National Corpus." Corpus Linguistics 25 Years On, ed. by Roberta Facchinetti. Rodopi, 2007)

Markings for Tense and Person

"[S]ome of the semi-modals, like have to and be going to, can be marked for tense and person:

- past tense:
He had to call the police. (CONV)

- third-person agreement:
Maybe she has to grow up a bit more. (CONV)

These semi-modals can sometimes co-occur with a central modal verb or another semi-modal."
(Douglas Biber, Susan Conrad, and Geoffrey Leech, Longman Student Grammar of Spoken and Written English. Pearson, 2002)


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Nordquist, Richard. "Definition of Semi-Auxiliaries and Semi-Modals." ThoughtCo, Feb. 19, 2018, Nordquist, Richard. (2018, February 19). Definition of Semi-Auxiliaries and Semi-Modals. Retrieved from Nordquist, Richard. "Definition of Semi-Auxiliaries and Semi-Modals." ThoughtCo. (accessed March 20, 2018).