Defective Verbs in English

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In English grammar, defective verb is a traditional term for a verb that doesn't exhibit all the typical forms of a conventional verb. 

English modal verbs (can, could, may, might, must, ought, shall, should, will, and would) are defective in that they lack distinctive third-person singular and nonfinite forms.  

As illustrated below, discussions of defective verbs commonly appeared in 19th-century school grammars; however, modern linguists and grammarians rarely use the term.

David Crystal's Take

"In grammar, [defective is] a traditional description of words which do not display all the rules of the class to which they belong. The English modal verbs, for example, are defective in that they do not permit the usual range of verb forms, such as an infinitive or participle forms (*to may, *shalling, etc.). Because of its pejorative connotations in general usage, the term needs to be used cautiously. It tends to be avoided in modern linguistic analysis (which talks more in terms of irregular forms and exceptions to rules), but will be encountered in studies of linguistic historiography. The distinction between 'defective' and 'irregular' needs to be appreciated: a defective form is a missing form; an irregular form is present, but does not conform to the rule governing the class to which it belongs."
(David Crystal, A Dictionary of Linguistics and Phonetics, 6th ed. Blackwell, 2008)

Beware and Begone

"Some verbs are termed defectivethey are such as want some of the parts ordinarily ascribed to verbs. Beware is a defective verb being used only in the imperative or to give a caution. . . . Begone may be accounted another defective verb like beware. Begone is a compound, made up of be and gone, that is get away; and beware is composed of be and ware found in aware, and wary."
(John R. Beard, "Lessons in English, LXII." The Popular Educator, Vol. 3, 1860)

The Defective Copula Is

"A defective verb is one which has not all the usual verbal forms. Is, the copula, is irregular. It is also defective as it has no imperative or autonomous forms, no verbal noun or verbal adjective."
(Irish-English/English-Irish Easy Reference Dictionary. Roberts Rinehart, 1998)

George Campbell on the Defective Verb 'Ought'

"[I]n order to express the past with the defective verb ought, we must use the perfect of the infinitive, and say for example, 'he ought to have done it'; this in that verb being the only possible way of distinguishing the past from the present."
(George Campbell, The Philosophy of Rhetoric, Volume 1, 1776)

Discussions of Defective Verbs in 19th-Century School Grammars

"What do you mean by a Defective Verb?
"A Defective Verb is a Verb that is imperfect; that is, that cannot be conjugated through all the Moods and Tenses; such as the Verb Ought, which has just been repeated.
"Which are the Defective Verbs?
"The Auxiliary Verbs are in general defective, because they have not any Participles; neither do they admit another helping Verb to be placed before them.
"Repeat the Defective Verbs.
"The Defective Verbs are, Do, Shall, Will, Can, May, Let, Must, Ought.
"How are the Defective Verbs used?
"They are always joined to the Infinitive Mood of some other Verb; as for example, 'I dare say, I ought to learn my lesson.'
"Must implies necessity, as I must do well, i.e. it is necessary that I should, or I am obliged to do so: why? because I ought, i.e. it is my duty to do well.
"Are the Auxiliary Verbs Have, and Am, or Be, Defective Verbs?
"No; they are perfect, and formed like other Verbs."
(Ellin Devis, The Accidence, or, First Rudiments of English Grammar, 17th ed., 1825)

A List of Defective Verbs

Defective verbs are those that can be used only in some particular modes and tenses. They are few in number and are as follows:

  • am
  • been
  • can
  • could
  • may
  • might
  • shall
  • should
  • was
  • will
  • would

Various Discussions on Defective Verbs

"Love is not a defective verb; you can use it in any mood and tense. You can say, I love, I loved, I have loved, I had loved, I shall or will love, I shall have loved, I may, can or must love: but can is a defective verb. You can say I can, but you cannot say I have can, I had can, I shall can or will can, I may can, or must can."
(J.H. Hull, Lectures on the English Language: Comprehending the Principles and Rules of Syntactical Parsing on a New and Highly Improved System, 8th ed., 1834)

"A defective verb is that which wants some of the modes and tenses; while an irregular verb has all the modes and tenses, though irregularly formed."
(Rufus William Bailey, English Grammar: A Simple, Concise, and Comprehensive Manual of the English Language, 10th ed., 1855)

 "Verbs which are not used in all the moods and tenses are called 'Defective.' But the student must not suppose from this that 'Defective' constitutes a separate or fourth class of verb. This is not at all the case. Quoth, for example, is a Defective verb, but also Intransitive. Again 'wit' is a Defective verb, but also Transitive. Again, 'may' is a Defective verb, but also Auxiliary."
(John Collinson Nesfield, English Grammar Past and Present: With Appendices on Prosody, Synonyms, and Other Outlying Subjects, 1898)

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Nordquist, Richard. "Defective Verbs in English." ThoughtCo, Apr. 5, 2023, Nordquist, Richard. (2023, April 5). Defective Verbs in English. Retrieved from Nordquist, Richard. "Defective Verbs in English." ThoughtCo. (accessed June 4, 2023).