Using Commas (Grammar and Punctuation)
 
A comma is used:

  • After setting the scene at the start of a sentence (e.g., Now I'm older, I understand. )
  • After transitional phrases like However, Consequently, or As a result (e.g., As a result, I now understand. )
  • After an interjection (e.g., Jeepers, now I understand. )
  • Before a conjunction joining two independent clauses (e.g., I like cake, and I like cheese. )
  • As parentheses (e.g., Janet and John Baxter, who live next door, adore cakes. )
  • To separate list items (e.g., bread, milk, and cheese () / bread, milk and cheese () – more on this below.)
  • After a long subject if it helps the reader (e.g., A, B, C, and D, are required to bake this cake. )
  • In numbers (e.g., 3,213 )
  • With the vocative case (e.g., I know your auntie, John. )
  • Before a quotation (e.g., She said, "I understand." )
 

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Using Commas after "Setting the Scene"


It is quite common for a sentence to start with words which "set the scene." These words usually state a place, a time, a condition, or a fact before the main part of the sentence. Words that "set the scene" at the start of a sentence are usually followed by a comma. You do not have to use a comma; i.e., it's not a strict ruling. It's just a common style. However, as it will help your reader, it is a useful style to adopt. For example:

  • In Paris, they simply stared when I spoke to them in French.
  • (sets a place)
  • At exactly 4 o'clock, two of the kidnappers re-entered the room.
  • (sets a time)
  • If you don't know where you are going, you will probably end up somewhere else. (Laurence J. Peter, 1919-1988)
  • (sets a condition)
  • As you were born here, it makes sense for my group to take the map.
  • (states a fact)
Often, the words that "set the scene" are a little harder to spot:

  • When a man tells you that he got rich through hard work , ask him "Whose?" (Don Marquis, 1878-1937)
  • (sets a time)
These "scene setting" words (or adverbial clauses or adverbial phrases as they're really called) vary hugely. You do not have to use a comma after an adverbial clause or phrase, but a comma will make it clear where the main clause starts. When an adverbial clause or phrase is very short (e.g., Nowadays, Now, Yesterday, Today), you are safer to omit the comma. For example:

  • When I was a boy, I was told that anybody could become President. Now I'm beginning to believe it. (Clarence Darrow, 1857 - 1938)
  • (First "scene setting" adverb – comma used. Second "scene setting" adverb – no comma required)
When an adverbial clause or phrase is at the end of a sentence, there is usually no need for a comma before it. When it is in the middle of a sentence, you should use commas if you think they will help the reader. For example:

  • Two of the kidnappers re-entered the room at exactly 4 o'clock.
  • Two of the kidnappers, at exactly 4 o'clock, re-entered the room.
Read more about using a comma after setting the scene

Using Commas after a Transitional Phrase


A transitional phrase is a term like However, Consequently, Therefore, and As a result. (There are others, but these are the most common.) A transitional phrase usually sits at the start of sentence and acts like a bridge to a recently mentioned idea (often an idea in the preceding sentence). A transitional phrase is usually followed by a comma. For example:

  • John has eaten at least two cakes a day for the last decade. As a result, he has been placed in a high-risk group for diabetes.
  • I think. Therefore, I am. Rene Descartes (1596-1650)
  • All progress is initiated by challenging current conceptions, and executed by supplanting existing institutions. Consequently, the first condition of progress is the removal of censorships. George Bernard Shaw (1856-1950)
  • Orthodox medicine has not found an answer to your complaint. However, luckily for you, I happen to be a quack.
A transitional phrase is never preceded by a comma. You can, on occasion, precede it with a semicolon (or a dash replacing a semicolon), but never a comma. That's called a run-on error.

Read more about using a comma after a transitional phrase

Using Commas after an Interjection


An interjection is usually a short word inserted into a sentence to express an emotion or feeling. Expressions such as yes, phew, and indeed are examples of interjections. Often, an interjection will sit at the start of the sentence but not always. It is normal practice to offset an interjection with a comma (or commas if it's in the middle of the sentence). In the examples below, the interjections are shaded:

  • Oh great, the boiler's broken down.
  • Yes, that's three out of three.
  • I understand your predicament, but, crikey, there is nothing we can do.
Note: If the interjection is to express a powerful emotion or feeling (and it's not in the middle of your sentence), then it can be followed by an exclamation mark.

Read more about using a comma after an interjection

Using Commas before a Conjunction


Words like and, or, and but are known as conjunctions. (There are other conjunctions, but these three are the most common.)

When a conjunction joins two standalone sentences (or independent clauses), it is usual to place a comma before it. For example (conjunctions shaded):

  • Lee can sing, and he can dance
  • (Here, the conjunction and is joining two standalone sentences: "Lee can sing." + "He can dance.")
  • Lee can sing, and dance
  • (Here, the conjunction and is not joining two standalone sentences. The words "and dance" are not a standalone sentence. This is just a list of things that Lee can do. This section is not about using commas in lists. That is covered below and in the lesson Using Commas in Lists.)
Here are some real examples:

  • No amount of time can erase the memory of a good cat, and no amount of masking tape can ever totally remove his fur from your couch. (Leo Buscaglia, 1925-1998)
  • When you have got an elephant by the hind leg, and he is trying to run away, it's best to let him run. (Abraham Lincoln, 1809-1865)
  • ("When you have got an elephant by the hind leg" is not a standalone sentence.)
Read more about using a comma before a conjunction
Read about the Oxford Comma

Using Commas for Parentheses


We all know that additional information (such as an explanation or an afterthought) can be offset with brackets. However, brackets are just one of the choices you have. You can also use commas or dashes. The information which is offset by commas, brackets, or dashes is called a parenthesis. The punctuation marks used to offset a parenthesis (i.e., dashes, brackets, or commas) are called parentheses.

Examples (with each example of parenthesis shaded):

  • The case has, in some respects, been not entirely devoid of interest.
  • At 4 o'clock yesterday, David Frost, a cleaner from the Lakes Estate, was charged with "dog napping" his former headmaster's poodle.
  • Joanne Baxter, who originally appeared as a witness, has been found guilty of handling stolen goods.
  • (Note: When a parenthesis starts with who or which (i.e., a relative pronoun), you should look to use commas as opposed to brackets or dashes. This is not a 100% rule, but commas are far more common when the parenthesis starts with a relative pronoun.)
Commas are often more suitable for formal writing than brackets, as brackets can make your work look a little unorganised. Also, commas are often preferable to dashes because dashes are quite stark. The disadvantage of using commas as parentheses (as they're called) is they can be easily confused with other commas in the sentence because — as you can see from this page — commas have lots of uses.

Read more about using commas to replace brackets

Using Commas in Lists


When writing a list in "sentence form" (i.e., not as bullet points), then it is normal practice to separate the list items using commas. For example:

  • Fish, chips, and peas
The big question is whether there needs to be a comma before the conjunction (in this example, it's the word and). Unfortunately, there is no simple rule for this.

The first part of the rule is easy enough: when there are just two items in a list, there is no need to use a comma between them.

  • Fish and chips
However, you can use a comma if you think it helps your reader.

  • The Bakerloo Line runs between Harrow and Wealdston, and Elephant and Castle.
When there are more than two list items in a list, then those following "US convention" should use a comma before the conjunction (usually and or or), and those following "UK convention" shouldn't. Therefore:

  • Fish, chips, and peas ()
  • Fish, chips and peas ()
Unfortunately, it gets a little more complicated than that. The comma before the conjunction is known as an Oxford Comma, and it is condoned by lots of individuals and organisations in the UK, and it is avoided by a few individuals and organisations in the US. Therefore:

  • Fish, chips, and peas () (If you're an advocate for the Oxford Comma.)
The bottom line is you should follow whatever convention those around you (e.g., your company seniors) follow. If there is no guidance like that, then follow whatever convention you like — but be consistent. If you have to break that convention for the sake of clarity, then have the confidence to do it. Clarity trumps style every single time.

Read more about using commas in lists

Using Commas after a Long Subject


When the subject of a sentence is made up of lots of elements, it is known as a compound subject. For example:

  • Janet is popular.
  • (Normal subject made up of one element: Janet)
  • Janet and John are popular.
  • (Compound subject made up of two elements: Janet and John)
  • The large gorilla is popular.
  • (Normal subject made up of one element: The large gorilla)
  • The large gorilla with the bright blue eyes and the albino lion cub with piercing pink eyes are popular.
  • (Compound subject made up of two elements)
In the last example, the compound subject is starting to get quite long. When a subject starts getting complicated, some writers like to show the end of the subject with a comma. Be aware that this is not a popular practice among many grammarians, but if you think it helps your reader, you can do it. For example:

  • Leaving a list of Internet passwords, increasing your life insurance and writing a will, will give you peace of mind while you are on operations.
  • (Here, the writer has used a comma after will to show the end of the subject. It is hard to argue that this comma does not help the reader.)
Read more about using a comma with a long subject

Using Commas with Numbers


Commas can be used every 3 decimal places in large numbers to make them more readable. For example:

  • 3,356
  • 12,128,153,356
  • 175,757.01
In Europe, the use of commas and full stops () / periods () is reversed. So, in Europe, the numbers above would be written:

  • 3.356 (in Europe)
  • 12.128.153.356 (in Europe)
  • 175.757,01 (in Europe)
Read more about using commas with numbers

Using Commas before Speech Marks


Words like He said, She shouted, The author stated, and She wrote often precede a quotation. A comma can be used after these words to separate them from the quotation. For example:

  • He said jokingly, "The world is my lobster."
  • Paul whispered, "Is he always that miserable?"
Note: You don't have to use a comma. Using nothing and using a colon after the words that introduce a quotation are also options.

In fact, it's your choice whether you follow your introductory words with a comma, a colon, or nothing. It depends on your desired flow of text. If you don't really care about the desired flow of text and you'd like some guidelines to help you decide which to use, then there is a useful guideline which states that a comma should be used for short quotations (six words or fewer) and colon should be used for longer quotations. (This is not a rule. It's a useful guideline.)

Read more about using a comma before speech marks

Using Commas with the Vocative Case


When words are used to address somebody (or something) directly, those words are said to be in the vocative case. In English, the vocative case is shown by offsetting it from the rest of the sentence with a comma (or commas if it's in the middle of the sentence). In the examples below, the words in the vocative case are shaded:

  • Do me the courtesy of shutting up, Alan.
  • Darling, can you take the casserole out the oven?
  • I know your sister, Jason.
  • Tell me it's good news, doctor.
  • And that, your Majesty, is how you make Eccles Cakes. I mean, it's how one makes Eccles Cakes.
Read more about using a comma when addressing someone
 
A READING TECHNIQUE NOT A WRITING TECHNIQUE

At school, many of us were told that a comma is where you take a breath. When you're reading someone else's work, that is fairly good advice. It is, however, terrible advice when you're thinking about where to put commas in your own work.

The rules for using commas are listed above (and on the left in more detail). There are quite a few of them, but most of them are intuitive or pretty simple. The idea that you should put a comma whenever you want your reader to take a breath is an erroneous extrapolation of a reading technique. It's not a writing technique.
 
 


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See also:

Apostrophes
Brackets
Colons
Commas
Dashes
Hyphens
Semicolons
Quotation Marks





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