Its is a possessive pronoun. It's is a contraction of "it is" or occasionally "it has." The apostrophe in it's is a mark of omission, not possession.
Examples:
When it's hot, the dog sleeps in its hiding place under the porch.
Usage Notes:
- "Its without the apostrophe is a possessive pronoun/determiner, pure and simple, as in left the dog on its own. Like the other pronouns in those roles (his, hers etc.), its has no apostrophe. What confuses the issue is the fact that nouns do have apostrophes when they are possessive, as in the dog's breakfast or a baker's dozen, suggesting that it's is the possessive pronoun for it. . . . In fact it's was used interchangeably with its for the possessive pronoun until around 1800, according to the Oxford Dictionary (1989). . . .
"From its debut in early C19, contracted it's has become increasingly common in everyday writing . . .. It compacts the space occupied by the functional words of the sentence, and like French c'est ('it is') enhances the flow of expository prose."
(Pam Peters, The Cambridge Guide to English Usage, Cambridge University Press, 2004) - "The possessive pronouns were a complete muddle in the 18th century. The grammarians were divided between apostrophized and unapostrophized forms, and frequently their own usage contradicted whatever conclusions they had reached. Over time the confusion has sorted itself out, and we now have a modestly consistent set of unapostrophized pronouns. So even though the apostrophe is on the rise . . ., we see no particular reason to go back to 18th-century usage. We recommend that you stick with its for the pronoun and it's for the contraction."
(Merriam-Webster's Dictionary of English Usage, Merriam-Webster, 1994)
Practice:
(a) Although _____ not yet fall, this tree is already losing _____ leaves.
(b) Either _____ dying, or _____ a sign that cold days are coming soon.
