When you should (and shouldn't) use a comma

The comma is one of the most versatile punctuation marks, but it's often used incorrectly

When you should (and shouldn't) use a comma

Ah, the humble comma. It’s one of the most versatile punctuation marks in the English language. However, that means it’s also often used incorrectly or overused.

Most people understand the basics of comma usage (if you don’t, check out our previous post on commas): as a ‘soft pause’ separating items in lists, clauses within a sentence or ideas. Think of it as a ‘breath’ within a sentence.

However, the specifics of exactly when you should use a comma can be confusing—and often rely on subtle distinctions between parts of a sentence. Here’s Outwrite’s guide to solving the sneaky comma quandaries that confuse people the most.

1. Introductory phrases

Many sentences start with a word or phrase that ‘sets the scene’ for the remainder of the sentence. This is called an ‘adverbial phrase’:

Slamming the door, Brian ran down the driveway.
However, the research clearly shows the latter to be true.
After opening the manhole, Theresa peered into the darkness.

The confusing thing here is that the comma is optional. While phrases like these are often followed by a comma, they don’t have to be — especially if it’s only one or two words. You should use a comma in the following situations:

  • If the adverbial phrase is four or more words long.
  • If you want to emphasize it or add a pause for effect.
  • If there is a chance of misreading the sentence without it.

All of the following examples are grammatically correct with or without a comma—but the addition of the comma is a style choice that improves the flow of the sentence.

After the game, the players will be attending a meet-and-greet with the competition winners.
Interestingly this is not the only option available.
In 1939 war broke out.

While adverbial phrases can be useful, sentences can usually be rephrased to avoid them. Outwrite’s paraphrasing tool can help you decide whether there’s a better way to make your point.

2. Interrupters, asides and parenthetical elements

Interrupters and parenthetical elements (also called ‘asides’) are clauses that add information, color or emphasis to a sentence but can easily be deleted without altering the sentence’s meaning. They are most often found in formal writing and fiction writing. Commas are used to denote these asides:

Pedro’s first attempt at making espresso, as you can imagine, was somewhat underwhelming.
The relevant tax law, which came into force in 2015, prevents companies from claiming flights as a deductible expense.
I, as a man of limited means, am rather loathe to spend too much of my money on a single night of debauchery.

Comma placement can get quite confusing when you have an adverbial phrase and an aside close together, like:

Even so, you may, as an alternative option, prefer to opt for a brighter colour scheme.

In this situation, you have a few options:

Remove either element altogether

Even so, You may, as an alternative option, prefer to opt for a brighter color scheme.
Even so, you may, as an alternative option, prefer to opt for a brighter color scheme.

Remove the comma from the adverbial phrase

Even so you may, as an alternative option, prefer to opt for a brighter color scheme.

Use dashes or brackets for the aside

Even so, you may—as an alternative option—prefer to opt for a brighter color scheme.
Even so, you may (as an alternative option) prefer to opt for a brighter color scheme.

Reposition the aside

Even so, you may prefer to opt for a brighter color scheme, as an alternative option.

Rephrase the sentence entirely

An alternative option would be opting for a brighter colour scheme.

3. Commas and adjectives

Believe it or not, there are specific rules that tell you when you should and shouldn’t use a comma with multiple adjectives. It’s all to do with the fact that there is actually a specific order in which you should apply adjectives in English – best explained by this Tweet:

If the adjectives are within one of these categories—e.g. opinion—they are said to be coordinate (modify the noun to an equal degree). If they are from different categories, then you shouldn't use a comma.

The best test for whether to use a comma is to switch the adjective order and read out loud. If the sentence still flows naturally, use a comma. If you sound like a maniac, put the words back the way they were and don’t use a comma.


The blue French horn was mounted on the restaurant wall (color–origin; not coordinate; no commas)
Sherlock Holmes was known to be an arrogant, aloof individual (both opinion adjectives; coordinate; comma)

4. For, And, Nor, But, Or, Yet, So

Many people get confused about whether to use a comma before words like but, and or so (often known as the FANBOYS coordinating conjunctions).


The answer is simple. You should use a comma if you are joining two independent clauses (separate ideas).

Alan is a good singer, but he’s a sensational guitarist.
The jury debated for the whole afternoon, and they eventually came to a unanimous verdict.

Do not use a comma if you aren’t joining independent clauses.

The play was long and boring.
The drill sergeant is strict but fair.

5. Restrictive and non-restrictive clauses

Now we’re into real ‘comma ninja’ territory. Restrictive and non-restrictive clauses is an area that sees even professional editors reaching for Google to work out if they need to use a comma. Nail this, and you can be sure that you’re in the grammar elite for sure.

Essentially, both restrictive and non-restrictive clauses provide extra information about something else in a sentence. However:

  • Restrictive clauses add necessary information, are often introduced by that or who, and do not require commas.
  • Non-restrictive clauses add non-essential information, are often introduced by which or who, and do require commas.

It’s a subtle difference, but an important one. As always, here are some examples to make it clearer.

  • Restrictive: The suspect in the lineup who has red hair committed the crime.
  • Non-restrictive: The second suspect in the lineup, who has red hair, committed the crime.
  • Restrictive: The Greek taverna that Agatha recommended was truly excellent.
  • Non-restrictive: The Original Greek Taverna, which Agatha recommended, was truly excellent.
  • Restrictive: The man who lives next door plays loud music all night long.
  • Non-restrictive: Our next-door neighbour, who is a man, plays loud music all night long.

The sharp-eyed among you may have noticed that a non-restrictive clause is very similar to an aside—and you’d be right. In fact, you can usually treat a non-restrictive clause in the same way as an aside without materially affecting the meaning of a sentence.

Still not sure? Let Outwrite help you!

Still struggling with commas, or don’t have the time to figure out whether a clause is restrictive or non-restrictive? Let Outwrite do it for you!

Outwrite’s free grammar checker will alert you if a comma is potentially misplaced—ensuring that your writing is always grammatically flawless.

Meanwhile, Outwrite’s suite of style suggestions and paraphrasing tool can suggest alternative ways of phrasing complex sentences—meaning you use fewer commas in the first place.

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