When to Use a Comma Before “As”

 

Posted by Jake Magnum | September 29, 2018 | Comma Corner

 

A mistake that I see writers (even good ones) make is that they forget to put a comma before the word as when a comma is needed (or they use a comma when they shouldn’t).

This article pertains particularly to sentences in which the word as separates two independent clauses. Here is an example of such a sentence:

George cleaned the house as his wife had asked him to.

The sentence above is perfectly grammatical. So is the sentence below:

George cleaned the house, as his wife had asked him to.

 
Although these two sentences are nearly identical, they mean different things. Adding that comma changed the meaning of the sentence by changing what the word as means.

As a rule, when writing a sentence with this structure, when you want as to mean because, place a comma before it. When you want as to mean in the way that or while, do not use a comma.
 
 
So, the first sentence above, which contains no comma, can be rephrased as

George cleaned the house in the way that his wife had asked him to.

The second sentence, which contains a comma, can be rephrased as

George cleaned the house because his wife had asked him to.

 
Note that, for certain sentences, there is only one correct decision regarding the use of a comma. See the example below:

George cleaned the house as he listened to the radio.

Putting a comma before as in this sentence would be a mistake. George clearly cleaned the house while he listened to the radio. It wouldn’t make sense for George to have cleaned the house because he was listing to the radio.
 
 
Thanks for reading! Stay tuned for more “comma magic” in the near future.