Valency
Impersonal verbs appear only as infinitives or with third-person inflection(s). In the third person, the subject is either implied or a dummy referring to people in general. The term "impersonal" simply means that the verb does not change according to grammatical person. In terms of valency, impersonal verbs are avalent, meaning that they altogether lack semantic arguments. In the sentence It rains, the pronoun it is a dummy subject; it is merely a syntactic placeholder - it has no concrete referent. In many other languages, there would be no subject at all. In Spanish, for example, It is raining could be expressed as simply llueve.
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