How to use ‘like’ and ‘as’

People often use the words like and as interchangeably. In speech–especially the informal kind–using like instead of as and vice-versa is generally accepted. For example, if you were to say, “Do your work like you were told,” instead of “Do your work as you were told”, probably no one would accuse you of being ungrammatical. When it comes to formal writing, however, like and as have distinct meanings to which usage should conform.

Note: Although both like and as have multiple meanings and usages, most of them are beyond the scope of this post, which covers the meanings that are usually confused.

How to use 'like' and 'as'

We tend to use like and as when making comparisons between things; however, there’s a subtle yet important difference between them.

Like indicates that something bears a similarity to another thing.
As indicates that something is done or performed like another thing.

Consider the following examples:

You are stealthy like a cat. (You are stealthy like a cat is stealthy.)
Please come in on your tiptoes, as before. (Come in on your tiptoes the way you came in before.)

Do you want the meringue to be light, like a cloud? (Do you want the meringue to be light like how a cloud is light?)
You must beat the egg whites as I do. (Beat the egg whites the same way that I beat them.)

Keeping these distinctions in mind, which words belong in the following statements? (Answers are at the bottom of this post.)

1. That man is acting (like, as) a buffoon.
2. Do (like, as) I do, not (like, as) I say.

3. She sings (like, as) a professional.
4. She sings (like, as) a professional sings.
5. Patrick Roy blocks the shots (like, as) he should.

Like and as are often used in the rhetorical device called a simile. A simile draws comparisons between objects using like or as. “Stealthy like a cat” and “as light as a cloud” are similes. Be careful when constructing similes; sloppy writing can make the sentence unclear or illogical.

“Like a violinist’s change in tune, Woody Allen directed a thriller after making mostly comedies.”

This simile compares a filmmaker to a change in tune, which is nonsensical. You can revise the simile thus:

“Like a violinist changing his tune, Woody Allen directed a thriller after making mostly comedies.”

The following is not a simile, but it is a construction I read all too often:

“As a great artist, I hope Caravaggio enjoyed his short life.”

Unless the writer is uncommonly proud of his own artistic talent, he means that Caravaggio was a great artist. Here’s one way to revise the sentence (it is also clearer than the original because each thought gets its own sentence):

“Caravaggio was a great artist. I hope he enjoyed his short life.”

Answers to examples above: 1. like 2. as, as 3. like 4. as 5. as