Do I need to use a comma before as?

Is a comma before ‘as’ ever mandatory?

Takeaway:

• A comma before as hints at a break, which suggests as is being used in the sense of because.

• A comma before as to mean because is not mandatory but can be helpful for clarity

• Some editors argue that the comma before as changes the meaning to because, despite the lack of editorial consensus on this issue
  

The different meanings of as

The style guides are quiet on this one.

Here’s my attempt, as not even the Chicago Manual of Style had an answer:

As can mean two different things:

As = because

As = while

• I smiled as I brushed my teeth

• I smiled(,) as I was happy

Now, conventional wisdom has it that if as means while, then no comma is needed.

What about when as means because?

When as means because, opinions are divided between:

1. The comma is necessary

2. The comma is optional but useful for clarity

For example, one proofreader, Jake Magnum, strongly suggests the comma changes the meaning to because:

In many sentences, if there is no comma before as, then as means ‘in the way that’ or ‘while’. When you insert a comma before as, its meaning changes to ‘because’.

Take these two sentences:*

1. I smiled as I was eating chocolate

2. I smiled, as I was eating chocolate

But does the comma turn the as into a because? Does it change the meaning, or does it hint that because is more likely?

I’d go for hint at rather than give meaning.

This is important as it comes up all the time in both fiction and academic writing.

Should I replace the word as with while or because?

In my editing and writing career, I've encountered the tip to remove the word as where possible because it can be ambiguous, and this can lead to issues with readability and clarity.

With the above example, this would involve making the following edits:

1. I smiled while I was eating chocolate

2. I smiled because I was eating chocolate

   
   

The main style guide I use (Chicago Manual of Style) is silent on this issue.

While on some occasions, making this edit can improve the clarity or rhythm or sonority of a text, it is certainly not an edit I would make when doing a light copyedit for traditional publishers. It's an edit I might occasionally make when line editing for a self-published author or an academic, but on many occasions, simply inserting or removing a comma before as would reduce the ambiguity.

In summary, this kind of edit can be heavy handed, or appropriate, depending on the context and the editing brief.

A comma before as: Conclusions

• A comma before as hints at a break, which suggests as is being used in the sense of because.

• A comma before as in the sense of because is not mandatory but can be helpful for clarity

• BUT: some (more prescriptivist) editors argue that the comma before as changes the meaning to because, despite the lack of editorial consensus on this issue

For a fresh perspective on publishing, check out my podcast:

Some extra confusion

Then we have the following:

• Andy didn’t finish the edit because he lost track of time. He finished it because he persevered.

• Andy didn’t finish the edit, because he lost track of time. He will try to improve his timekeeping, so he can finish it tomorrow.

  
  

If we switch to as, ambiguity reigns:

• Andy didn’t finish the edit as he lost track of time. He finished it because he persevered.

In this (rare) situation, it’s probably worth changing the ‘as’ to ‘because’ unless the context makes it clear. This sentence, for example, has three possible meanings (!):

• She didn’t ask him out as he was changing.

*I’ve deliberately kept the sentences short so we can stay focused on the task at hand