 Most people are familiar with the apostrophe's two primary uses, possessives and contractions. To make a noun possessive, we add apostrophe s. The llama's teeth means the llama possesses the teeth. To make a contraction, we show which letters have been removed by replacing them with an apostrophe. The llama's been fed means the llama has been fed. But those two situations overlap and resemble so many other situations that even conscientious and knowledgeable writers sometimes get mixed up. In fact, most apostrophe errors come from trying to implement the right convention in the wrong situation. Probably the most common example of this is the word it's. If we had a sentence like, It's showing its teeth. Which it's would need an apostrophe? Well, that first one seems like a contraction for it is. And it is. We've taken out a letter and we show that with the apostrophe. The second one looks like a possessive. And it is. The it possesses the teeth. So adding apostrophe s seems logical. That's the problem. The right logic in the wrong situation. We actually don't use an apostrophe. And here's why. The apostrophe s rule is for nouns only, like llama, not for pronouns, which are words that stand in for nouns. He, she, they, it. Instead, we have special pronouns that show possession. We would say his teeth, her teeth, their teeth. We don't use apostrophes for any of those words, not even the one that ends in s. High's teeth, he's teeth? No, his teeth. For the same reason, we don't use any apostrophe for the possessive pronoun we need in our example. It's. It's teeth. This confusion comes up often when we're dealing with plurals since they also require adding an s. For example, what happens if we want to make a word plural and possessive? What if something belongs to more than one llama? Well, rather than adding apostrophe s, we add s apostrophe. The llama's field, the llama's fence, the llama's protective instincts. The one s serves a kind of double function, showing both pluralization and, along with the apostrophe, possession. That fluidity can make it easy to get confused, especially with situations where the plurals seem unconventional. For example, what if your last name is Jones and you want to send a holiday card from your whole family? The name already looks plural, so how do you pluralize it? Add an apostrophe? Well, no, it's not possessive, and it's not a contraction, so the apostrophe doesn't figure in. Like usual, we just add an s. Or in this case, as with most words that already end in s, we add es. The Joneses. No apostrophe needed. But even this rule has exceptions. One example would be straight a's. As in, next year I'm going to get straight a's. It's a plural, so we just add s, right? Well, look what happens. It makes a word that holds an alternate meaning, as. That's confusing to readers. Straight a's? Straight a's? What? We alleviate that confusion by adding an apostrophe, a's. That is, as Oakland baseball fans know, the correct convention for this plural. That's a pretty rare situation, but a pretty common purpose for the apostrophe, to alleviate confusion by distinguishing word forms that sound the same. They're writing, they're writing. The words sound exactly the same, but the apostrophe lets us know which one we're dealing with, just as it does with its and its. Really want to be a stickler? Make sure your apostrophe is curved. The vertical version is a catch-all mark, invented to reduce the number of keys on a typewriter. And usually, we save it for measurements, such as feet and inches or minutes and seconds. And make sure your apostrophe faces left, not right. Even if it comes at the beginning of a contraction, like twas. The one that faces right is an opening single quotation mark. A topic we'll cover in another video. But if we're honest, those are conventions that even most sticklers overlook, and ones that possibly belong to the realm of typography more than grammar. It just goes to show the minute differences and deep similarities that make the apostrophe an especially tricky piece of punctuation.