Like vs. As

The Union vs. The Confederacy. Vampires vs. werewolves. Harry Potter vs. Voldemort. These are all ferocious battles.

But none of them compare to the war that grammarians are raging over: the use of like as a conjunction.

Okay, maybe we're exaggerating. (Maybe.)

But seriously—grammarians can be brutal. They may not fight with bayonets or magic wands, but their words and expert grip on grammar can pierce straight through the heart.

Here's the deal. In common usage, like is now used as a conjunction. For example, "You look like you've seen a ghost." However, the word like traditionally has been known as a preposition that means similar to. The very definition of a preposition is that is has a noun or noun phrase as its object. In the sentence "You look like you've seen a ghost," what follows like is not a noun or noun phrase—it's an entire independent clause, "you've seen a ghost." Sounds like the behavior of a conjunction, no?

The word as is the conjunction to be used here. The previous sentence is traditionally written as: "You look as if/though you've seen a ghost."

If you're going with common usage, don't sweat it. But if you're taking a grammar quiz (like the one we have in this module), only use like when it's followed by a noun or noun phrase. Otherwise, use as if or as though to connect your clauses, please.