In linguistics, a defective verb is a verb with an incomplete conjugation. Defective verbs cannot be conjugated in certain tenses, aspects, or moods. Linguistics is the scientific study of language, which can be theoretical or applied. ... It has been suggested that Verbal agreement be merged into this article or section. ... In linguistics, conjugation is the creation of derived forms of a verb from its principal parts by inflection (regular alteration according to rules of grammar). ... Grammatical tense is a way languages express the time at which an event described by a sentence occurs. ... In linguistics, the grammatical aspect of a verb defines the temporal flow (or lack thereof) in the described event or state. ... It has been suggested that prohibitive mood be merged into this article or section. ...

Defective verbs in English

The most commonly recognized defective verbs in English are the class of preterite-present verbs, can, may, shall, and mote/must, plus will (which was not historically a preterite-present but has joined the class in modern English). Though these verbs were not originally defective, in most varieties of English today, they occur only in a modal auxiliary sense. However, unlike normal auxiliary verbs, they do not regularly conjugate in the infinitive mood. Therefore, these defective auxiliaries do not accept each other as objects. Additionally, they do not regularly appear as participles. The preterite-present verbs are a small group of anomalous verbs in the Germanic languages. ... In linguistics, many grammars have the concept of grammatical mood, which describes the relationship of a verb with reality and intent. ...

Beyond the modal auxiliaries, beware is a full-fledged defective verb of English: it is used as an imperative ("Beware of the dog") and an infinitive ("I must beware of the dog"), but very rarely or never as a finite verb, especially with inflectional endings (*bewared, *bewares). Certain other verbs are defective only in specific constructions. For instance, in the "try and" construction (meaning 'try to'), try may only be used in forms with no inflectional endings. Thus I try and do it every week is possible, but not *She tries and does it or *She tries and do it.

Impersonal verbs in English

Impersonal verbs such as "rain" and "snow" share some characteristics with the defective verbs in that conjugations such as "I rain" or "they snow" are not often found; however, the crucial distinction is that impersonal verbs are "missing" certain forms for semantic reasons — in other words, the forms themselves exist and the verb is capable of being fully conjugated with all its forms (and is therefore not defective) but some forms are unlikely to be found because they appear meaningless. An impersonal verb is a verb that cannot take a true subject, because it does not represent an action, occurrence, or state-of-being of any specific person, place, or thing. ...

Nevertheless, native speakers can typically use and understand metaphorical or even literal sentences where the "meaningless" forms exist, such as:

• I rained on his parade.
• I tried to help by clearing their drive but instead I snowed them in.

Contrast the impersonal verb "rain" (all the forms exist even if they sometimes look semantically odd) with the defective verb "shall" (only "I shall" and "I should" are possible):

Defective verbs in Latin

Latin has defective verbs that possess forms only in the perfect tense system; such verbs have no present tense forms whatsoever. However, these verbs are present in meaning. For example, the first-person form odi and infinitive odisse appear to be the perfect tense of a verb such as *odo, but in fact have the present-tense meaning "I hate". Similarly, the verb memini, meminisse is conjugated in the perfect: For other uses, see Latin (disambiguation). ...

meminī

meministī

meminit

meminimus

meministis

meminērunt

Instead of "I remembered", "you remembered", etc., these forms signify "I remember", "you remember", etc. Latin defective verbs also possess regularly formed pluperfect forms (with a simple past tense meaning) and future perfect forms (with a simple future tense meaning). Compare deponent verbs, which are passive in form and active in meaning. A deponent verb is a verb that is active in meaning but takes its form from a different voice, most commonly the middle or passive. ...

Examples from other languages

• French: frire (lacks a passé simple), éclore (lacks an imperfect)
• Spanish: abolir (this is disputed, but some contend that there is no *él abole, for example)
• Polish: widać, słychać (the only form of these verbs that exists is the infinitive)
• Portuguese: a large number of Portuguese verbs are defective in person, i.e., they lack the proper form for one of the pronouns in some tense. The verb colorir ("to color") has no first person singular in the present (thus requiring a paraphrase, like estou colorindo ("I am coloring") of the use of another verb of similar meaning, like pintar ("to paint").
• Dutch: in Dutch there are four defective verbs (apart from deponent verbs and impersonal verbs): plegen (to be used to), zullen (shall), zijn (to be) and wezen (to be). The verbs zullen and plegen do not have any perfect tenses. Furthermore, zullen does not have any future and past future tenses, and its conditional mood does not exist. The verbs zijn and wezen are used to complete each other's conjugation. A part from the infinitive (zijn versus wezen (to be)) and gerund (het zijn versus het wezen ((the) being)), only the simple present subjunctives of both verbs exists (ik zij versus ik weze (I be)). For all other forms there only exists one form:e.g. zijnde (being) (present participle of zijn), ik was (I was) (indicative past simple of wezen). (See Dutch conjugation)