Use commas for clarity

Commas are tricky because sometimes we use them to indicate pauses, and other times we use them for grammatical purposes. And sometimes, if the meaning is clear, we leave them out.

Commas can add clarity or cause confusion. Common examples given to illustrate this are:

Let’s eat, grandma.
Let’s eat grandma.

No thanks to you.
No, thanks to you.

When to use commas

We use commas for the following purposes.

Separate items
Use commas to separate items in a list or after adjectives describing a noun.

The agenda included credit card fraud, security measures and whistleblowing policies.

It was a long, boring and unnecessary meeting.
The meeting was long, boring and unnecessary.

Separate clauses
Use a comma to separate two independent clauses joined by a coordinating conjunction (and, but, for, or, nor, so, yet).

The proposal looked promising, but some information was missing.

You can often omit the comma if the meaning is clear without it.

Add extra information
Use commas to indicate extra information that could be deleted from the sentence and it would still make sense.

Ms Marika Weinberg, chief executive officer, presented the prizes. (Extra information provided about a noun or noun phrase is known as an appositive.)
The meeting, which was meant to be held at 9am, was postponed.

Separate ‘interrupters’ and end statements
Use commas before and after words and phrases that ‘interrupt’ the sentence, or separate an end statement.

She is, however, going to resubmit the proposal.
The proposal will be accepted this time, won’t it?

Introduce information
Use commas for introductory phrases or clauses, or to introduce quotes. If the introductory phrase is short and the meaning is clear, commas are often omitted.

Last month, we submitted our proposal to the board. (This comma could be omitted.)
While we were waiting for more data, the company went into liquidation.
She said, ‘We should discuss this proposal further.’ (You could use a colon instead of a comma.)

Serial or Oxford commas

A comma is sometimes needed between the last two items in a list for clarity. This is known as the serial or Oxford comma.

The invoice included travel, goods and services tax, and consulting work.

There is an urban myth regarding the serial comma about a woman who left her estate to Jane, William, Mary and Anne. Jane and William argued that the estate should be divided into three, with Mary and Anne sharing a third. An Oxford comma would have prevented this dispute (Jane, William, Mary, and Anne).

Common comma mistakes

Common comma mistakes include the comma splice and run-on sentences.

Comma splice
A comma splice occurs when you join two independent clauses with a comma instead of a conjunction or semicolon.

The meeting was postponed, the CEO was sick.

Rewritten:

The meeting was postponed because the CEO was sick. (conjunction)
The meeting was postponed; the CEO was sick. (semicolon)
The meeting was postponed the CEO was sick. (dash)

Run-on sentence
A run-on sentence has two independent clauses that are joined without a conjunction or punctuation mark.

The next board meeting is in September you should start preparing now.

Rewritten:

The next board meeting is in September, so you should start preparing now. (conjunction)
The next board meeting is in September; you should start preparing now. (semicolon)
The next board meeting is in September you should start preparing now. (dash)
The next board meeting is in September. You should start preparing now. (new sentence)

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