You've probably already been in doubt about the conjugation of some verbs, right? When this happens, a simple grammar query can solve several questions. However, there are some verbs that cause even more doubts about the conjugation, they are called defective verbs.
Defective verbs are those that have a deficiency in their conjugation, that is, because they do not have all the verbs, they cannot be conjugated in certain people, tenses or modes. There are several reasons why certain verbs are classified as defective, among them are the euphony and the meaning. For example, the verb to color, which does not present the conjugation in the first person singular of the present indicative (I) and the forms derived from it: Nobody speaks "I color the design", even because this conjugation sounds strange, as it produces a dissonant sound that does not respect the aspect of euphony.
Even if you don't know what defective verbs are, you'll certainly make linguistic substitutions that sound nicer, like
“I paint the design”. Another example of a defective verb is the verb retrieve, which is not conjugated in the first person singular indicative, as well as in the present subjunctive and in the negative imperative. In these situations, the ideal is that adequate substitutions are made, respecting the euphony and the context, because if the replacement is not adequate, the construction of meanings will certainly be impaired.There is still another detail regarding defective verbs: Some people confuse defective verbs with so-called impersonal verbs, those that do not refer to a subject. This is the case of verbs that indicate meteorological phenomena, such as rain, flash, thunder, snow, etc., and the verb be, which will only be used on third parties. As for impersonal verbs, it is necessary to make an important caveat: if they are used figuratively, they can be conjugated in different ways, such as: "rained audience applause” or “The wind blew strong in the bands of Minas Gerais”. Therefore, be aware of the differences between defective and impersonal verbs, thus avoiding hasty classifications.
By Luana Castro
Graduated in Letters
Source: Brazil School - https://brasilescola.uol.com.br/gramatica/verbos-defectivos.htm