Often times we use the words like and as interchangeably in a sentence. And actually this became a big grammar issue back in the 1950's, when the cigarette company Winston debuted an ad campaign that said the cigarettes taste good like a cigarette should. That was the incorrect use of the like, because actually it should have been as. I'll let you know the difference. Like is a preposition, whereas as is a conjunction. So like is used as a preposition to show the relationship between words in a sentence. And as is used as a conjunction to connect ideas. So now I'll give you an example of how we might use like or as in a sentence. We'll start with like. So, I might say, "You fight like a girl." In this case, I need a preposition.
And you can hear it would sound a little strange to say "You fight as a girl." On the other hand, if I say something like "You fight as if you were the strongest girl in the world." In this case, we need as, a conjunction. On one hand we have the fighter that we are talking about and on the other hand we have the strongest girl in the world. And as kind of links those two ideas. One way that you can kind of spot this in a sentence is to remember that like is usually followed by a really simple phrase without a verb. So here you can see "You fight like a girl." All we get after the word like is a girl. There is no verb. With the word as, it's often followed by a more complex phrase that includes a verb.
And that holds true in this example, "You fight as if you were the strongest girl in the world." Well, here, were is our verb. So, if you have a sentence like this and you're trying to fill in the blank with like or as, remember that little tip. So now that I've taught you the rule, it might make sense why Winston's ad campaign was incorrect. Winston should have said "Winston's taste good, as a cigarette should." As being a conjunction that links Winston cigarette with the way that a cigarette should taste. And thanks to Grammar Girls website for that great bit of history. I hope this clears up the difference between like and as, and helps you recognize which one to use in your sentence.