To hear most people tell it, writing something like I like you’re coat is pretty similar to writing Say what you will about the Fascists, but at least Mussolini got the trains running on time. Namely, it marks you as an idiot with only a rudimentary understanding of the English language (or Italian history in the second sentence). “There are very simple, clear-cut rules about which your/you’re is used where!” cry the grammarians, and I admit that in the past I have cried with them. But if writing the Preposterous Apostrophes series has taught me anything, it’s that nothing is clear-cut when apostrophes are involved. So why do people get so confused between possessive pronouns and contractions (or in the case of they’re/their/there, pronouns, contractions, and locatives)?
I think the problem is best seen in the its/it’s distinction. The former is a possessive pronoun, the latter a contraction. People get awfully riled up about this confusion, but just try to tell me it’s not a reasonable mistake to make. It is singular, it ends in a consonant that sounds nothing like an s, and it’s sure noun-like. Well, nouns that don’t end in s-like sounds always get ‘s to make their possessives, so why shouldn’t it be it’s? The answer is that, due to the vagaries of English, pronouns are not treated like nouns when possessives are formed, silly! Of course, there are situations where it’s would be a proper possessive, because this is English and nothing should be easy about it:
(1) Get Over It‘s lack of commercial success despite Sisqo’s starring role remains a mystery.
(2) The IT’S-IT‘s popularity is limited off the West Coast, but it shouldn’t be.
(3) Cousin Itt‘s hair is the inspiration for my new hairstyle.
Now, in both of these cases, it is a noun, while in its situations, it is a pronoun. One could argue that in these sentences the ‘s is not attaching directly to it (or Itt), but rather to a phrase that ends in it. But I think that in cases where one can refer directly to it as a noun, it’s is far better than its:
(4) Upon seeing the ghost, Mr. Czolgosz shouted, “It… it… it… it’s a ghost!” It‘s repetition in his stammered statement underscored his fear.
(Of course, any reasonable speaker of English not trying to make a middling point about the occasional acceptability of it’s would have said “the repetition of it” in (4).) Anyway, my point is that it is only because it is a pronoun that it’s is not the standard form for the possessive of it. So why does being a pronoun matter? I don’t actually know exactly, but here’s my speculation:
English does not have a particularly extensive case system; a given word is usually written & pronounced the same whether it is the subject or object of a verb (Paolo ate the book vs. the book ate Paolo). In a lot of other languages, such as Estonian, Russian, and German, just to focus on Central and Eastern Europe, noun phrases are written differently depending on what role they perform in the sentence:
(5) Der Tisch gab den Tisch des Tisch(e)s dem Tisch(e)
The table gave the table of the table to the table.
(I cannot guarantee this example is perfect German, as I copied it verbatim from Wikipedia.) In (5), the subject has nominative case and so its article is der, whereas the second table is the direct object and gets accusative case. The other two tables have genitive case (possessive case, as with English ‘s) and dative case (a to-phrase in English), respectively. English does have a little bit of case marking, but it only appears on pronouns (I ate the book vs. The book ate me), and even then it doesn’t appear on all pronouns (It ate you vs. You ate it).
What’s my point with this digression in Germanic morphology? Simple: Possessives are manifestations of genitive case, and pronouns in English manifest case differently from nouns. So it’s not all that surprising that pronouns have different possessive forms than they would if they were nouns. But given that it is the same in nominative and accusative cases, just like a noun, it is a little surprising that it‘s possessive is a special case, especially since its and it’s sound identical. So yes, there is a clear-cut rule that the possessive of the pronoun it is its, but that’s competing with a separate rule saying that ‘s is the possessive marker.
Same thing with your/you’re and their/they’re; if you think of the rule that possessives involve an apostrophe (for there is no possessive of a noun that does not include an apostrophe) before you think of the special rule that pronouns’ possessives do not involve apostrophes, you could easily write you’re or they’re for the possessives. I’m not saying it’s justified, per se. But it is a reasonable error — certainly more reasonable than one would expect given the invective spewed at those who make this mistake.
And, for the history buffs in the audience, let me point out that its is a somewhat recent addition to the language. Its earliest written citation in the OED is 1598, although it was apparently in use colloquially before then. In fact, through the 19th century, it’s and its were in competition to be the possessive form of it, and it looks like it’s was more popular in the 17th century. So it isn’t obvious that its should be the possessive pronoun, or at least it wasn’t at first.
The Preposterous Apostrophes series as it stands: