I promised I’d start off with simple topics. I went on a brief digression with my opinion of hone in vs home in, but today I’ll get back on track.
The seemingly age-old confusion between it’s and its is a very good place to start. The concept is simple, and, once you understand what each word is there for, you will always get this one right. Always. Except when you’re not paying attention…which happens to all of us now and then. But let’s be realistic here: there is no excuse for making this error in anything that you’ve proofed even once.
The simple non-explained grammarian explanation:
it’s is a contraction
its is possessive
Let’s take this deeper.
A contraction, of course, is created when two words (do not, is not) or, less commonly, more than two words (would not have), or, rarely, a single word (madam, forecastle), are shortened: don’t, isn’t, wouldn’t’ve, ma’am, fo’c’sle. Letters and spaces are dropped and apostrophes are inserted.
Possession is usually shown by the addition of “apostrophe s”: ‘s. Or just the apostrophe ‘, or in some cases s’s. It shows ownership: That cookie belongs to Mike. The stick next to it belongs to Tina. You’d show possession this way: If you take Mike’s cookie, he’ll beat you with Tina’s stick.
Possession can be plural as well, for both the possessing entity and the objects possessed. Those decrepit dune buggies belong to our families. If so: We need new tires for the families’s dune buggies. Sane style guides recommend that you drop the final s from that awkward s’s form. You wouldn’t pronounce it “families-es” and it’s nice to see that most don’t ask you to write it that way, either.
So, this all brings us back to its and it’s.
It’s is simply the contraction of it is or it has (or, in rare cases, it was).
Its is an exception to the normal rules of English possession: it’s possessive, but it uses no apostrophe.
How do you distinguish, consistently and correctly, between the two? Very easily.
If you can expand the it’s in the sentence to it is (or it has), then you’ve used it correctly. If that expansion causes a non-grammatical sentence, you’ve used it incorrectly.
“It’s a very easy rule” becomes “It is a very easy rule.” “It’s been fun” becomes “It has been fun.” You’re good to go.
“That other rule has it’s problems” however, becomes “That other rule has it is problems” (or “has it has problems”), which makes no sense grammatically. So it can’t be the contraction it’s form. It must be the possessive its form instead. The rule works in reverse as well. If you change the possessive its to it is or it has and the sentence no longer makes sense, then you had it right to begin with.
I mentioned above that it’s can also be a contraction for it was. I expect to take some flack for this, so I’ll clarify. Despite the advice I give on this blog, I am primarily a descriptivist: I can explain most of the rules, but I’m more interested in observing how the language is actually used, rather than telling people what they “must” or “must not” do with it. Observation tells me that, any rules of the language to the contrary, it was is sometimes contracted to it’s.
English used to have a fairly common contraction for it was: ’twas. But ’twas is pretty much extinct in actual use, limited now to comic and ironic effect (at least in American English). Since we have nothing else to take it’s place, you’ll sometimes encounter it’s used for it was in speech (I can think of only a single use in writing, and that has an aura of jest about it).
My advice is to avoid using it’s for it was in writing. It’s not that I don’t like it, in and of itself. The problem is that it’s ambiguous. In every case I’ve seen, it’s for it was can easily be confused for it is (including the “Sun” example, above). If there’s one thing you want when you’re communicating, it’s clarity. If you must use it’s for it was, restrict yourself to conversations where the context keeps the meaning clear – and where you’re physically present to deal with any confusion if it’s not!