I was reading 8th book of Manhattan Guides, the idioms chapter. They explain the difference between "act like" and "act as". Their explanation appears more logical as they explain when it means "to function" we should use "as", when it talks about behaving in similar manner, we should employ "act like". But here's the twist, they point out that OG 12th edn also tests this idiom in problem #65 and the explanation by OG claims that "act like" should only be used with people. Manhattan guys deny this explanation advising the students not to follow it. And it's not the first time i witnessed such case, during my review of the rest of the guide books, they made couple of claims like this one. As far as I know OG is published by GMAC, the (good) guys who come up with the questions and set the standards... shouldn't we believe what they say? After all, these are the guys who evaluate the answers in actual test? I'm confused....
I'm happy to help with this.
This is a very tricky topic --- it's understandable that you're confused.
Rule #1: we use "like" for isolated nouns, and "as" for full noun + verb clauses---
(The technical way to say that is: "like" is a preposition, and "as" is a subordinating conjunction.)
1) Like my dog, I get excited when the mailman comes.
2) I enjoy reading poetry as my dog enjoys chewing a bone.
Rule #2: the verb "act" is a special case --- the idiom "to act like" means "to behave as, to comport one's self as" ---- this can properly be applied only to a person (or conceivably to a very intelligent animal, if we were able to attribute to it imitative behavior). We categorically cannot apply the idiom "to act like" to an inanimate object, so we need "act as". Notice, the general rule, Rule #1, is almost always the case: this is just a bizarre idiom concerning this particular verb.
Thus, "the breakwater of rocks" must "act as a buffer."
This is one of those cases in which there's a valid general rule, but the specific idiom trumps the general rule.
Here's a related blog you may find helpful.
https://magoosh.com/gmat/2012/gmat-sente ... omparison/
Does that make sense? Let me know if you have any further questions.
Mike
