Writing: Colons — Video lesson

- [Instructor] I'm on question 22 here on this writing and language test. And that question starts here. Through such initiatives, beaver populations are doing what they do best: engineering healthier, more stable ecosystems. All right. Let's figure out what kind of question this is. Our choices are all different kinds of punctuation, right? So no changes. This semi-colon. B is em dash. C is a colon, and D is a comma. So that means we're looking at a punctuation question. Now, how best to tackle it? You're going to see about five or six punctuation questions on your SAT. And a great tip in general with punctuation questions is to check the clause before the piece of punctuation. Colons, periods, and semi-colons all have to come after independent clauses, for example. But a comma can't follow an independent clause unless it's being joined to another independent clause with a coordinating conjunction like and or but. So let's go back and check the clause and see what we learn. Remember, an independent clause has to be able to stand on its own as a sentence. So we need a subject and a main verb. I see beaver populations as our subject, and are doing as our verb. So this is an independent clause here. But a semi-colon can only be used to unite two independent clauses. So what's after the punctuation? Engineering healthier, more stable ecosystems. Okay, I don't see a subject or a main verb. Engineering here has no helper verb, so it's a participle. And that means we treat it like a noun. This isn't an independent clause. So that means that the semi-colon is no good. We can safely knock out choice A. Let's test the next choice with an em dash. So em dashes are usually used in pairs to set off asides, but they can also be used like colons to set up examples. But also like colons, they have to come after independent clauses when they're used this way. Okay. That checks out so far. But there's something else happening here in this choice. There's that comma after engineering, which chops up the second part of the sentence in this weird, awkward way. Engineering, comma, healthier, more stable ecosystems. When really, healthier more stable ecosystems is the object of engineering. It's what the engineering accomplishes. So that comma makes this weird and awkward and not our choice. And the same thing is happening in choice D because it also has that comma after engineering. Right? You're not supposed to separate a verb from its object with a comma. And that leaves C as our answer. It uses a colon to introduce an example which is one of the colon's many functions. And we know it's appropriately used because it comes after an independent clause. So with punctuation questions generally, your strategy is this. First, look on either side of the punctuation being tested and check the phrases and clauses that piece of punctuation is connecting. And then ask yourself, what is the sentence trying to do? Is it setting up a list? Is it connecting to independent clauses? Use your punctuation knowledge to eliminate things that obviously don't work. And then look for subtler clues, like those rogue commas in the worked example. You will never have to do choose between two correct answers. There will always be some other kind of error that spoils the other choices.