A dummy pronoun (or, more formally, pleonastic pronoun) is a type of pronoun used in non-pro-drop languages, such as English, when a particular argument of a verb 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 the statement It's raining, for example, the word it is a dummy pronoun, referring to a nonexistent agent. Unlike a regular pronoun, it does not refer to, nor can it be replaced by, a definite noun.
When used as subjects, dummy pronouns are typically used only in simple transitive statements of the It's raining variety, and unlike actual pronouns, cannot translate consistently into the passive voice; for instance, one might easily transform the sentence It bit me into I am bitten by it, but It's raining on me cannot be transformed into *I'm being rained on by it. The grammatically correct form would be simply I'm being rained on.
As objects, dummy 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 into intransitive verbs, e.g. do → do it, "to engage in sexual intercourse"; make → make it, "to achieve success"; get → get it, "to comprehend". Of course, these terms have simply arisen as arbitrary truncations of longer phrases, and this is by no means a formal process; the common meaning of make, for instance, is not in any way related to the definition of make it, the latter deriving from a now-obsolete transitive expression.
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