My is used before a noun to show that something belongs to or is connected with the speaker, as in “my book” or “my idea.” It marks personal possession or relationship.
From Old English *mīn*, the possessive form of *ic* “I,” related to German *mein* and Dutch *mijn*. Over time, English developed *my* for use before consonant sounds and kept *mine* mainly for use on its own.
“My” is a tiny word that does huge social work: it marks what you claim as yours—objects, opinions, even mistakes. Interestingly, kids often say “mine” before they say “my,” showing how strong the feeling of ownership is. The grammar of possession grows out of the psychology of possession.
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