More often than not, people will use like when they should be using as, because the word like has become so ubiquitous in modern language. So let's start things off easily by asking what the difference is between these two words, since many people tend to use them interchangeably.
In the context of our discussion today, like is a preposition, whereas as is a conjunction. For previous discussions on these types of words, please check them out here and here. Perhaps the easiest way to remember how to use these two words is to ask yourself this question: "Is there a verb following this word?" If your answer is "yes", you would use as. Otherwise, use like. Another, perhaps simpler way to make your decision is if you can use the word resemble in the sentence. If you can, then you'll want to use like because "looks like = resembles".
Let's take a look at a few examples, courtesy of Evil Queen Regina and Snow White fighting
Wrong: "For a grown woman, Snow White, you are acting as a child!"
Right: "For a grown woman, Snow White, you are acting like a child!"
Wrong: "For a grown woman, Snow White, you are acting like a child would!"
Right: "For a grown woman, Snow White, you are acting as a child would!"
In the first example pair, we see that there isn't a verb following like/as, so like is the correct choice. In the second example, there is a verb following, so as is correct.
A quick side note here about the examples above: Because of the colloquial way that people tend to speak, especially in the United States, using these words incorrectly in dialogue can be an authorial choice, provided you're consistent with it. It's not grammatically correct, but it's socially acceptable and makes a modern character potentially more relatable.
In the end, what's easiest to remember for using these words is whether or not an action follows it. If it does, use as. If it doesn't, use like. If you're still not sure, see if you can substitute the word resemble in its place. If you can, use like. If you can't, use as.
- Like Versus As @ Grammar Girl
- "Like" Versus "Such As" @ Grammar Girl
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- Like vs. As
- Like and As
- Misue of Like and As