I asked my son, when he was about 15, so some years ago, why he used an apostrophe when he wrote " it's bone". He was writing about a dog. He said, well, the bone belongs to the dog. It's his."
I then mentioned his, hers and its / he, she it.
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I asked him what he would say "it's" meant if it stood alone, and he answered "it is, or it has."
I get the feeling quite a few people don't get beyond this stage unless it is pointed out to them. Spell checkers and auto correct on keyboards often confuse the issue too.
What Would You Do in this Position?
Estranged Son and Future Granddaughter