Some writers incorrectly use like in sentences, such as the title of this blog post, that require as. Other writers, wary of like, avoid the term even in sentences that require it, so they write: He swam as a fish. Below is some guidance so you can learn to use these terms as a good writer does—like an expert.
As can be a conjunction or a preposition.
In My father makes pasta from scratch as his mother did when he was a child, the conjunction as introduces the clause his mother did.
In My father cooks as a professional chef at a restaurant, as is a preposition preceding the noun phrase professional chef.
Most usage experts recommend using like only as a preposition.
In My father cooks like a professional chef, the preposition like precedes the object a chef.
So since like is a conjunction and as can be one, how do you choose which term to use?
Wilson Follett has a handy rule: “as tells in what role or capacity the deed is done; like introduces a comparison” (199). So in the example My father cooks as a professional chef at a restaurant, the writer indicates that the father is a professional chef. In the example My father cooks like a professional chef, the father is not a professional chef; the writer is only comparing him to one.
Follett, Wilson. Modern American Usage: A Guide. Hill and Wang, 1966.
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