Do I need to use a comma before ‘as’?

Updated: Nov 10

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

  • BUT: 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, and the Grammar Table’s poll suggested no consensus among editors.


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’?


However, 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 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’. Jake Magnum

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 the ‘hint at’ rather than ‘give meaning’.


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


To conclude:

  • 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 prescriptive?) editors argue that the comma before ‘as’ changes the meaning to ‘because’, despite the lack of editorial consensus on this issue

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





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Andrew Hodges, PhD is a copyeditor and developmental editor who specializes in editing fiction for science fiction and fantasy writers. His expertise is in worldbuilding and cultural considerations when crafting setting in stories.


He is an advanced professional member of the CIEP, a member of the EFA, and an ALLi partner member.


You can contact him here, or feel free to leave a comment below!


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