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. Verbs indicating weather, such as to rain, are often impersonal. A verb is a part of speech that usually denotes action (bring, read), occurrence (decompose, glitter), or a state of being (exist, stand). Depending on the language, a verb may vary in form according to many factors, possibly including its tense, aspect, mood and voice. ... The subject of a sentence is one of the two main parts of a sentence, the other being the predicate. ... A weather verb is a special verb form found in English and certain other languages which, in its basic sense, is capable of taking only a dummy pronoun as its subject. ...

In some languages, such as English, French and German, an impersonal verb always takes an impersonal "dummy pronoun" (it in English, il in French, es in German) as its syntactical subject: The English language is a West Germanic language that originates in England. ... A dummy pronoun (or more formally expletive pronoun or pleonastic pronoun) is a type of pronoun used in non-pro-drop languages, such as English, when a particular argument of a verb (or preposition) is nonexistent, unknown, irrelevant, already understood, or otherwise not to be spoken of directly, but a...

It snowed yesterday.

Il a neigé hier. (French)

Es schneit gestern. (German)

In some other languages (necessarily null subject language and typically pro-drop languages), such as Portuguese, Spanish and Italian, an impersonal verb takes no subject at all, but it is conjugated in the third-person singular, which is much as though it had a third-person, singular subject: A null subject language, in linguistic typology, is a language whose grammar permits the omission of an explicit subject. ... A pro-drop language (from pronoun-dropping) is a language where pronouns can be deleted when pragmatically inferable. ... The subject of a sentence is one of the two main parts of a sentence, the other being the predicate. ... The word conjugation has several meanings: Grammatical conjugation is the modification of a verb from its basic form. ... Third person redirects here, but can also mean: Third Person, a New York City improvising trio A perspective (storytelling) Grammatical person, in linguistics, is deictic reference to the participant role of a referent, such as the speaker, the addressee, and others. ... The word singular may refer to one of several concepts. ...

Nevó ayer. (Spanish)

Nevou ontem. (Portuguese)

In some languages, some verbs meaning existence are also impersonal. ...

Há livros. / Há um livro. (Portuguese: There are books / There is a book)

Hay libros. / Hay un libro. (Spanish: There are books / There is a book)

In these languages, however, there may be personal verbs with more or less the same meaning: The introduction to this article provides insufficient context for those unfamiliar with the subject matter. ...

Existem livros. / Existe um livro. (Portuguese: There exist books / There exists a book)

An impersonal verb is different from a defective verb in that with an impersonal verb, only one possible syntactical subject is meaningful (either expressed or not), whereas with a defective verb, certain choices of subject might not grammatically possible, because the verb does not have a complete conjugation. A defective verb is a verb with an incomplete conjugation. ...