You have likely noticed this before, or puzzled over it. It happens all the time. Your is used when you’re is the correct form, or vice versa.
The confusion comes, I think, from the presence of the apostrophe, as well as the fact that both words sound the same.
Sometimes apostrophes indicate possession, as in Beth’s pen or Owl’s talon, and other times apostrophes indicate two words contracted into one. Beth can’t find her pen, and Owl won’t let her see what’s clutched in his talons.
In the case of your and you’re, the apostrophe indicates a contraction. You’re means you are, and the apostrophe takes the place of the a. Your (with no apostrophe in sight) is the one that is a possessive.
You have to go by the sense of the word, and use your memory. If the meaning of the word as used in the sentence is you are, then you spell it you’re. Otherwise, it’s your.
Take another look at the title of this post and the ensuing conversation between the Owl and me.
“It’s your responsibility to make sure you’re using the correct word.”
“Whooooooose responsibility?” asked Owl.
“Yours,” I said, quickly adding, “Not that you’re doing it incorrectly.”
These examples show which word is correct, by the meaning of the word. The responsibility belongs to you to make sure you are using the correct word.
If the word answers the question “Who does it belong to?” then use your.
If the word answers the question “Who is?” use you are = you’re.
Note that usually when the apostrophe indicates possession, there is an s following it. However, in this case, yours does NOT have an apostrophe. If you feel yourself on the verge of writing your’s, ask yourself if the context of the sentence means you are or means something belongs to the you of the sentence.
The only time there would be an apostrophe is if it means you are, and you would never say you ares, would you? So leave the apostrophe out. Yours.
And we will sign this,
Beth and the Owl