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he's or his

He's is the short form of 'he is' or 'he has'.

For example: " Don't be scared - he's very friendly."

His is a possessive pronoun, it is used to show something belonging to or connected with a man, boy or male animal that has just been mentioned.

For example: "Mark just phoned to say he'd left his coat behind. He's very worried. Do you know if this is his?"

See the grammar pages for more information on possessive pronouns.