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 reference to the argument (a pronoun) is nevertheless syntactically required. In linguistics and grammar, a pronoun is a pro-form that substitutes a noun or noun phrase with or without a determiner, such as you and they in English. ... Pro-drop language (from pronoun-dropping) is a language where pronouns can be elided (deleted) when considered unnecessary or redundant by the speaker. ... The English language is a West Germanic language that originates in England. ... A syntactic verb argument, in linguistics, is a phrase that appears in a relationship with the verb in a proposition. ... A verb is a part of speech that usually denotes action (bring, read), occurrence (to decompose (itself), to glitter), or a state of being (exist, live, soak, stand). Depending on the language, a verb may vary in form according to many factors, possibly including its tense, aspect, mood and voice. ... In grammar, a preposition is a type of adposition, a grammatical particle that establishes a relationship between an object (usually a noun phrase) and some other part of the sentence, often expressing a location in place or time. ... The first meaning of the term syntax, originating from the Greek words συν (sun, meaning ‘together’) and ταξις (taxis, meaning sequence/order), can be described as the study of the rules, or patterned relations that govern the way the words in a sentence come together. ...

In It is obvious that the violence will continue, for instance, it is a dummy pronoun, not referring to any agent. Unlike a regular pronoun of English, it cannot be replaced by any noun phrase. In linguistics, a grammatical agent is an entity that carries out an action. ... In linguistics, a noun phrase is a phrase whose Head is a noun. ...

The "weather it"

In It is raining, the verb to rain is usually considered semantically impersonal, even though it appears as syntactically intransitive; in this view, the required it is to be considered a dummy word. In the main, semantics (from the Greek semantikos, or significant meaning, derived from sema, sign) is the study of meaning, in some sense of that term. ... 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. ... In grammar, an intransitive verb is an action verb that takes no object. ...

However, there have been a few objections to this interpretation. Chomsky has argued that the it employed as the subject of English weather verbs ("weather it") can control an adjunct clause, just like a "normal" subject. Compare: Avram Noam Chomsky (born December 7, 1928) is Institute Professor Emeritus of linguistics at the Massachusetts Institute of Technology. ... 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. ...

She brushes her teeth before having a bath.

→ She brushes her teeth before she has a bath.

It sometimes rains after snowing.

→It sometimes rains after it snows.

If this analysis is accepted, then the "weather it" is to be considered a "quasi-argument" and not a dummy word.

Some linguists like D.L. Bolinger go even further and claim that the "weather it" simply refers to a general state of affairs in the context of utterance. In this case, it would not be a dummy word at all.

Dummy objects

In English, dummy object pronouns tend to serve an ad hoc function, applying with less regularity than they do as subjects. Dummy objects are sometimes used to transform transitive light verbs into intransitive verbs, e.g. do → do it, "to engage in sexual intercourse"; make → make it, "to achieve success"; get → get it, "to comprehend". Prepositional objects are similar, e.g. with it (now old fashioned), "up to date"; out of it, "unconscious". In linguistics, the object of a transitive verb is one of its core arguments, which generally represents the target of the verbs action. ... In grammar, a transitive verb is a verb that requires both a subject and an object. ... In grammar, an intransitive verb is an action verb that takes no object. ...

References

• Chomsky, Noam (1981) Lectures on Government and Binding. Dordrecht: Foris., cited in http://www.ling.helsinki.fi/sky/julkaisut/SKY2004/Alba-Salas.pdf.
• Bolinger, D. L. (1977). Meaning and form. English Language Series, 11. London: Longman.