<rant>I understand that on this forum, there are many member who reside in countries where english is not the first language. I also understand that many of us (myself included) type our messages as we speak, colloquially, and as such, we use improper sentence format. I am partial to comma splices [as well as nested parenthesis and brackets (I go off on tangents a lot)], since they convey the way I speak, with slight pauses between thoughts. All that aside, I twitch every time someone writes "you're watch is beautiful" or "I've seen there watches, and their beautiful" or "you're watch is in better shape then mine".
SO! To keep me from twitching, and to keep me from correcting individual members' posts, I'm just going to do a thread on the correct usage, and hope that people might remember it in the future.
Your is the second person possessive adjective, used to describe something as belonging to you. Your is nearly always followed by a noun.
What is your name?
Is this your pen?
You're is the contraction of "you are" and is often followed by the present participle (verb form ending in -ing).
You're going to be late.
Is that what you're wearing?
Unlike then, than is not related to time. Than is used in comparative statements.
He is taller than I am.
Other than the interest on a small inheritance, he had no income.
Then is used either as a time marker or with a sequence of events.
I took all of the exams in the morning, and then I spent the rest of the day catching up on sleep.
Back then we knew what was expected of us.
I bought apples from this orchard last summer, but I seem to remember paying more for them then.
They're Their There:
Their is a possessive pronoun. It always describes a noun.
Note the spelling of their. It comes from the word they, so the e comes before the i.
There is an adverb meaning "that location." It is sometimes used with the verb to be as an idiom. It is spelled like here which means "this location."
They're is a contraction of they are. Note the spelling: The a from are is replaced by an apostrophe.
Examples: Their dog has fleas. (possessive of they)
I put the collar right there. (that location)
There are five prime numbers less than ten.
(with to be)
They're 1, 2, 3, 5, and 7. (contraction of they are)
Sorry.... Drives me nuts!