One of the things that really bugs me about the “grammar police” type is their inability to distinguish grammar from spelling. I am sick of reading “grammar” posts on your vs. you’re. It is not a grammar mistake – it’s just a spelling mistake. Native English speakers absolutely know the difference. I am 100% sure that the mental grammar of an English speaker, the only grammar that really matters, distinguishes the lexical items your and you’re, even if the speaker doesn’t always know how to spell them.
If people really couldn’t tell the difference between your and you’re, and if this really was a grammatical problem and not just a spelling mistake, there would be evidence beyond the occasional confusion in writing. Here’s an actual grammatical property to consider: you’re is a contraction of a verb and a pronoun, and in question formation, this verb get moved before the subject, e.g. You’re happy becomes Are you happy? (I wrote about this movement in more detail recently.)
Note that when there’s a contraction, you have to “undo” it and move only the verb are to the front. The pronoun can stay put. If English speakers were truly, utterly confused about the difference between you’re and your, then you would expect them to occasionally “undo” the wrong one:
(1a) You’re walking your dog.
(1b) Are you walking your dog?
(1c) *Are your walking you dog?
(2a) Your parents are home.
(2b) Are your parents home?
(2c) *Are you parents are home?
No one would ever utter the (c) forms. No one would try to extract an auxiliary that isn’t really there. Those are clearly ungrammatical sentences in English. For everyone. The confusion between your and you’re is a spelling mistake. Plain and simple. Those words have really similar phonetic forms, and so people get confused about how to write them. Or they just have a “slip-of-the-fingers” when typing (cf. a “slip of the tongue”). But no one is fundamentally confused about it.
Now, I’m not saying it is therefore totally cool to just write whatever you like. Of course not. This kind of sloppiness suggests that the writer otherwise doesn’t care about detail or about the quality of her own work. I can maybe excuse one such mistake on an assignment or in formal correspondence (everyone screws up now and again), but too many and I start wondering.
Edit: If you liked this post, you might like my more recent attempt at the same topic