An impersonal construction is a verbal construction which lacks a specifiable subject. There is either no subject or its syntactic position can only be occupied by an expletive element. illustrates the alternative.

An impersonal verb form is a verb form heading an impersonal construction. If it conjugates for person, it is of third person. An impersonal verb is a verb which in its basic valency and voice only heads an impersonal construction. German grauen is an impersonal verb; neither ich ‘I’ nor du ‘you’ could be the subject of a sentence like . In several European languages, weather verbs like rain and snow are impersonal verbs.

That the subject is not specifiable means that it designates nothing. This entails that it is non-referential. However, a subject may be non-referential, but still designate something, as in . Therefore the non-referential nature of the subject is not a defining feature of the impersonal construction.

The term ‘impersonal’ misleads to the interpretation that the subject is not a person. While this is true of an impersonal construction and implies that an impersonal verb of a language whose verbs conjugate for person only occurs in the third person, there are constructions and verbs whose subject cannot be a person, but which still take a specifiable subject, as in and .

Thus, although amount and happen do not take a personal subject, they are not therefore impersonal verbs.

Since the passive demotes the basic subject, many impersonal constructions are passive constructions, as in .