A couple hundred years ago when punctuation was becoming standardized in our language, someone should have been smart enough to come up with a different symbol for possessives versus contractions. Using an apostrophe for both leads to some of the most common errors in writing.
Every grammar or style book goes into great detail about apostrophe use for singular possessives, plural possessives, possessives of common versus proper nouns, apostrophes in contractions, apostrophes with numbers, and other forms. And the occasional and highly confusing exceptions to the rules.
Here are the three most frequent apostrophe errors:
It’s/Its: This is one of the exceptions to the rule for making a noun possessive. The possessive of it is its, without an apostrophe. That is in order to distinguish it from the contraction of it is (or sometimes it has), which is it’s.
It’s not the apostrophe’s fault that its usage is so confusing.
You’re/Your: You’re is the contraction of you are. Your is the possessive of you.
Your house is where you’re most comfortable.
Let’s/Lets: Let’s is the contraction for let us; it is not a possessive. Lets is a verb meaning permits or allows; it is not a plural nor possessive form.
Let’s go to the library, if your mother lets us.
AN apostrophe tip:
Never use an apostrophe to make a noun plural. The Smiths have a new house, not the Smith’s have a new house.
Oh, and one of my pet peeves: The contraction of until is ‘til, not till (and never ‘till).