Writing Skills
From Rsgc Library
Common Word Usage, Spelling and Punctuation Problems
- Its and it's
Its is the possessive form of it (The cat licked its paws) and it's is a shortened form of it is (It's raining again) or occasionally it has (I don't know if it's come). - Oxford Pocket Fowler's Modern English Usage, p. 374
- There, their and they're