Commas (,)

Published by at August 17th, 2021 , Revised On September 21, 2021

Commas are required to be used when there is a need to split a sentence into different parts to give more meaning and clarity to your writing. Among all types of punctuations in the English language, commas are perhaps the most commonly used type of punctuation and perhaps also the most misused.

This article provides the most notable commas rules and the mistakes you should avoid when using commas in a sentence.

Before we get deeper into the rules of a comma, it would make sense to learn when and when not to use a comma in a sentence.

A comma must be used when:

  • You introduce a sentence

Moreover the work could not be completed.
Moreover, the work could not be completed.

  • You isolate a non-restrictive clause

Mohammad who was a great sprinter could not pursue the sport he loved due to financial issues.

Mohammad, who was a great sprinter, could not pursue the sport he loved due to financial issues.

  • You use a coordinating conjunction to join independent clauses

The wheat is in high demand so it is costly.

Wheat is in high demand, so it is costly.

You should not use a comma;

  • Between independent clauses

The king died,  the empire collapsed.

The king died: the empire collapsed.

  • Between compound objects or subjects

A zinger burger, and pack of French fries make for a mouthwatering meal.

A zinger burger and a pack of French fries make for a mouthwatering meal.

  • Between a verb and its subject

He is, too short to marry her.

He is too short to marry her.

Introducing a Sentence with a Comma

When a transition word (moreover, furthermore, however, ideally, hence, therefore) is used to introduce a sentence, it should be followed by a comma.

When a transition word (moreover, furthermore, however, ideally, hence, therefore) is used to introduce a sentence, it should be followed by a comma.

Therefore we can conclude that this research achieved its objectives.

Therefore, we can conclude that this research achieved its objectives.

When an explanatory clause is used to introduce a sentence and establish the basis for the main part, it is recommended to separate the introductory clause and the main part of the sentence with a comma, particularly when the introductory phrase is 4 to 5 words long.

Considering John’s recent performances as a Baseball striker it’s hard to imagine his team going into the tournament without him.

Considering John’s recent performances as a Baseball striker,  it’s hard to imagine his team going into the tournament without him.

Dependent vs Independent Clauses

When a group of words contains both the verb and the subject, it is called a clause. A single sentence can consist of many clauses, and therefore, it is vitally important to understand when to separate them with a comma or another appropriate type of punctuation.

The types of the clauses and the interrelationship determines whether or not there is a need to put a comma between them.

A dependent clause generally represents an incomplete idea, so it depends on another clause to complete the sentence. On the other hand, an independent clause is complete in nature and stands on its own as a complete sentence. Therefore, there is no need to use a comma with independent clauses.

When a sentence starts with a dependent clause, a comma must be placed after it.

Since distance learning courses have emerged, the number of international students coming to the UK have decreased.

When a dependent clause comes after the independent clause in a sentence, it may or may not be necessary to use a comma, particularly if it adds enough clarity and context to the independent clause.

the number of international students coming to the UK have decreased since distance learning courses have emerged.

Using Commas in Compound Sentences

When two independent clauses appear in a sentence they must be joined through a coordinating conjunction, a color, or a semicolon. Examples of coordinating conjunctions are “so, yet, are, but, nor, or and).

A comma should be used to separate the two independent clauses when they are connected to each other through a coordinating conjunction.

Albert Einstein left many wondering with his theory of relativity, but people of the time were convinced.

Electric cars are the future of the transport industry, so we are excited about them.

A comma needs to be placed between clauses that could be perceived as full sentences on their own.

The Comma Slice Error

A comma slice error occurs when two independent clauses are used together in the same sentence. Some examples of the comma splice error are;

  • She always drinks water before eating her meal, it is good for health.
  • The student could not complete the coursework in a timely manner, he loved watching movies.
  • The researcher selected the primary research methodology, it provides more reliable findings.

The six independent clauses in the above three examples could all stand as full sentences by themselves, and therefore, there was no need to separate them with a comma.

It is relatively easy to avoid the comma splice error. Simply split the two independent clauses into two different sentences that stand alone on their own.

You could also use another type of punctuation such as dash, colon or semi-colon or a conjunction to establish the interconnection. The following examples show how your chosen approach could produce unlike results.

Incorrect with a Comma Splice Error

She always drinks water before eating her meal, I fell in love with her.

The student could not complete the coursework in a timely manner, he loved watching movies.

The researcher selected the primary research methodology, it provides more reliable findings.

Splitting into Two Different Sentences

She always drinks water before eating her meal. It is good for health.

The student could not complete the coursework in a timely manner. He loved watching movies.

The researcher selected the primary research methodology. It provides more reliable findings.

Connect with a Conjunction

She always drinks water before eating her meal because it is good for health.

The student could not complete the coursework in a timely manner as he loved watching movies.

The researcher selected the primary research methodology since it provides more reliable findings.

Connect with Another Form of Punctuation

She always drinks water before eating her meal – It is good for health.

Using Commas in Restrictive and Non-Restrictive Clauses

Make sure not to use a comma around a restrictive clause.

A restrictive clause restricts the meaning of the sentence because it gives meaning to the main clause in a sentence.

Children who are disabled  are vulnerable.

The above sentence contains information about specific types of children who are experiencing disabilities of some kind. If we remove the restrictive clause from the above example, the sentence will become confusing because it will give a message that all children are vulnerable.

A non-restrictive clause is the exact opposite of a non-restrictive clause because the main clause of the sentence is not dependent on it. The meaning of the sentence can be well understood even if it was not there in the first place.

A non-restrictive clause only adds an extra layer of information to the main point, and therefore, it should be enclosed within commas.

Children, who are adorable, can be difficult to handle at times.

The non-restrictive clause ‘who are adorable’ in the above sentence is an additional piece of information. If we removed it, the original meaning of the sentence will still remain unchanged.

No Comma Between a Verb and Its Subject

It is imperative to recognize the relationship between different words in a sentence to avoid comma mistakes. A comma should never be used between a verb and its subjects.

This dissertation, investigates the industrial use of bamboo as an alternative to plastic.

This dissertation investigates the industrial use of bamboo as an alternative to plastic.

Another mistake that you need to be mindful of is the use of a comma between a verb and its subject (s) when the sentence includes modifiers. The presence of modifiers can make you overlook the obvious connection between verb and subjects.

The politicians who were involved in corruption, pleaded guilty.

The politicians who were involved in corruption pleaded guilty.

However, if a non-restrictive clause separates the subjects from verb, it should be enclosed within two commas. Examples of non-restrictive clauses include ‘However’ and ‘Therefore’.

The dissertation, which consists of six chapters, investigates the industrial use of bamboo as an alternative to plastic.

The politicians who were involved in corruption, however, pleaded guilty.

Use of Serial Commas

A serial comma, also known as Oxford comma, is used before the conjunction and the last item of list. However, it is not mandatory to use a serial comma in most cases. If you do choose to use it, make sure to be consistent throughout your writing.

With Serial Comma Examples

The toilet accessories included a razor, a toothbrush, a soap dish, a toothpaste, a soap, and a toothbrush holder.

He bought apples, oranges, pineapples, and grapes from the supermarket.

Without Serial Comma Examples

The toilet accessories included a razor, a toothbrush, a soap dish, a toothpaste, a soap and a toothbrush holder.

He bought apples, oranges, pineapples, and grapes from the supermarket.

In some cases, a serial comma must be used to give more clarity and meaning to the sentence. This is especially important for sentences the end with a conjunction.

The top causes of climate change are plastic pollution, sound pollution and air and atmosphere pollution.

The top causes of climate change are plastic pollution, sound pollution, and air and atmosphere pollution.

When the i-tems at the end of the list clarify the introductory phrase in a sentence

The air and atmosphere in the above sentence is a single type of pollution, and therefore, the use of comma is recommended to avoid confusion.

Another example of serial comma is when the list items at the end of the sentence describe the introductory phrase.

She was responsible to look after her two pets, Mike and Mohammad.

She was responsible to look after her two pets, Mike, and Mohammad.

The use of comma between the list items in the above sentence clarifies that pets, Mike and Mohammad are two separate items. If a serial comma had not been used, it would have appeared as if Mike, Mohammad were the names of the pets.

Avoid Separating Compound Objects or Subjects from the Verb

When two objects or subjects are related to a verb then make sure not to separate them with a comma.

Compound Object

The football team coach gave a t-shirt, and pair of snickers to each player.

The football team coach gave a t-shirt and pair of snickers to each player.

The t-shirt and the pair of snickers are two objects that are connected to the same verb, so there is no need to use a comma to separate the two objects.

Compound Subject

Mike and Mohammad are always looking to help the poor.

Mike and Mohammad are always looking to help the poor.

Both Mike and Mohammad share a relation with the verb to be, and so a comma should be not be placed between them.

Avoid Separating Compound Predicates

The part of the sentence that contains the verb is called the predicate. However, when two or more verbs share a relation with the same subject then the predicate is referred to as the compound predicate. A comma should not separate the words in sentences that contain a compound predicate.

They showed up, and cleared the mess.

They showed up and cleared the mess.

Be extra careful when there are other phrases or words that separate the two verbs. For example,

The dog leaped in joy, and ran towards its owner.

The dog leaped in joy and ran towards its owner.

The dog in the above sentence is doing two things; leaping in joy and running towards its owner. However, both verbs are connected to the same subject – dog, and so there is no need to use a comma between them.

Sometimes, you might need to use a comma if there is the need to highlight the difference between the two verbs, for example;

The respondents filled out the questionnaire, and sent their responses to the researcher.

The respondents filled out the questionnaire and sent their responses to the researcher.

A comma is acceptable if you wish to introduce conjunction to highlight the difference between the verbs, for example;

The respondents filled out the questionnaire but refused to send their responses to the researcher.

About Alvin Nicolas

Nicolas has a master's degree in literature and a PhD degree in statistics. He loves to write, cook and run. Nicolas is passionate about helping students at all levels.