In linguistics, 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. The term weather verb is also sometimes used, since such weather-indicating verbs as to rain are usually impersonal.
In some languages, such as English, French, German and Dutch, an impersonal verb always takes an impersonal pronoun (it in English, il in French, es in German, het in Dutch) as its syntactical subject:
In some other languages (necessarily null subject languages and typically pro-drop languages), such as Portuguese, Spanish, Occitan, Catalan, Italian, Romanian, in Hungarian and all the Slavic languages, 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.
In the auxiliary language Interlingua, verbs are not conjugated by person. Impersonal verbs take the pronoun il:
In the planned auxiliary language Esperanto, where verbs also are not conjugated for person, impersonal verbs are simply stated with no subject given or implied, even though Esperanto is otherwise not a null subject language:
The Celtic languages also possess impersonal verbal forms, though their use is usually translated into English by forms such as 'one sees' (Welsh: gwelir), 'one did' (Welsh: gwnaethpwyd), 'one is' (Irish: táthar) etc., where the 'one' is taken to be an empty subject. For weather, personal verbs are used in Celtic languages, e.g. Welsh Mae hi'n bwrw eira 'it is snowing'.
Verbs meaning existence may also be impersonal.
However, sometimes there are intransitive verbs with more or less the same meaning:
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 be grammatically possible, because the verb does not have a complete conjugation.
Some linguists consider the impersonal subject of a weather verb to be a "dummy pronoun", while others interpret it differently.