Overview
In Modern English, it is a singular, neuter, third-person pronoun.
Morphology
In Modern English, it has only three shapes representing five word forms:
it: the nominative (subjective) and accusative (objective) forms. (The accusative case is also called the "oblique".)
its: the dependent and independent genitive (possessive) forms
itself: the reflexive form
Historically, though, the morphology is more complex.
History
Old English
Old English had a single third-person pronoun – from the Proto-Germanic demonstrative base *khi-, from PIE *ko- "this" – which had a plural and three genders in the singular. The modern pronoun it developed out of the neuter, singular. The older pronoun had the following forms:
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