Comma before and after conjunctions

Comma after so
When so is used to mean therefore, it is a transitional adverb. So, it should be followed by a comma.

• I was not feeling well. So, I decided to consult a doctor.

Semicolon before And
A coordinating conjunction that merges two clauses into one is usually preceded by a comma. However, the comma can be left out when the clauses connected by the conjunction are very short.

• The boys sang, and the girls danced.

The comma is not exactly necessary in the example given above because the clauses are short. However, it is possible.

If one or both of the clauses connected by a conjunction contains a comma, we sometimes use a semicolon instead of a comma. Note that although a semicolon is possible here, it may look dated.

• Alan, Sophie and Mira absolutely love the steak pie; but Maria, a staunch vegetarian, detests it.

Here the two clauses are connected by the coordinating conjunction but. However, we separate them using a semicolon because the second clause contains two commas.

Note that a semicolon is not exactly necessary here. A comma will work just fine. In fact, a comma tends to be more common than a semicolon.

• Alan, Sophie and Mira absolutely love the steak pie, but Maria, a staunch vegetarian, detests it.

That-clauses
Commas are not used before that-clauses.

She said that she would come. (NOT She said, that she would come.)

Notes
A that-clause is essentially a noun clause that serves as the subject or object of the verb in the main clause.

Comma before subordinate clauses
When subordinate clauses come at the beginning of sentences we usually separate them with a comma. The comma can be left out when the subordinate clause goes after the main clause.

Because he had been reading my letters without my knowledge, I was quite angry with him.

I was quite angry with him because he had been reading my letters without my knowledge.

Comma with conjunctions

Conjunctions do not normally cause major grammatical errors. However, students sometimes incorrectly use two conjunctions to connect two clauses. In English, we need just one conjunction to connect two clauses. If there are four clauses in the sentence, we need just three conjunctions to connect them.

Another common problem is the confusion about the placement of comma. Sometimes we use a comma before a conjunction. Sometimes we do not use a comma.

When subordinate clauses begin a sentence, we usually separate them from the rest of the sentence with a comma. When the subordinate clause goes after the main clause, the comma can be left out.

While there are no simple rules regarding the placement of comma with conjunctions, the following guidelines should help.

Comma before the final item in a list

We use commas to separate items in a series or list. The last two items in a list are usually connected by and. In British English, it is quite unusual to use a comma with and.

• I visited France, Germany, Italy, Britain and Spain. (GB)
• I visited France, Germany, Italy, Britain, and Spain. (US)

Notes

When there are just two items in a list, a comma is not necessary before and.

I met John and Mary. (NOT I met John, and Mary.)

When there are more than two items, some people prefer to use a comma before and. Some people do not use a comma. There is no right or wrong answer here. Pick a convention and then stick with it. That’s all.

The comma that goes before the conjunction is called the Oxford Comma. Interestingly, although it is called Oxford Comma, it is mainly used by writers in the US.

• I bought some milk, eggs, and butter. (List with Oxford Comma)
• I bought some milk, eggs and butter. (List without Oxford Comma)

Common comma errors

Comma is a very common punctuation mark. It is used to indicate a slight pause within a sentence. Students often misuse commas. If you don’t know whether a comma is appropriate in a particular sentence, try reading the sentence aloud. If the sentence sounds better without a pause, omit the comma. If it sounds better with a pause, add a comma. Don’t scatter commas throughout your writing.

Common mistakes in the use of commas

Do not place a comma between two verbs.

• The children were singing and dancing. (NOT The children were singing, and dancing.)

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

• She was not feeling very well, but she went to work.

However, the comma can be avoided when the clauses are too short.

When an adverb clause comes at the beginning of a sentence, we usually separate it with a comma.

• After she finished her homework, she watched TV.
• As I was walking down the street, I saw him driving a Ferrari.

The comma is not necessary when the main clause comes at the beginning of the sentence.

• She watched TV after she finished her homework.

Two clauses that are not connected by a coordinating conjunction cannot be separated by a comma.

• She was tired and went to bed. (NOT She was tired she went to bed.)

When a sentence begins with a conjunctive adverb, you need to separate the adverb with a comma.

• She was tired. Therefore, she decided to get some rest. (NOT She was tired. Therefore she decided to get some rest.)

Semicolon before a transitional phrase

A transitional phrase is essentially a word or phrase used to show the relationship between two clauses or paragraphs. Transitional phrases (also called conjunctive adverbs) usually come at the beginning of a sentence and are separated from the rest of the sentence with a comma. Common examples of transitional phrases are: however, therefore, consequently, furthermore, moreover, even as etc.

Read the sentences given below.

• The train was an hour late. In spite of this, I managed to get to the meeting in time.

Here the phrase ‘in spite of this’ acts as a transitional adverb. As you can see, it does not connect the two clauses. It merely shows how ideas are connected.

We usually use a full stop before a transitional phrase. Sometimes writers use semi-colons instead of full stops. An advantage of using this method is that it makes the transition between the sentences even more seamless.

• She had little chance of success. Nevertheless, she decided to enter the competition.
• OR She had little chance of success; nevertheless, she decided to enter the competition.
• I cannot attend your wedding. However, my blessings are always with you.
• OR I cannot attend your wedding; however, my blessings are always with you.

Note that you cannot use a comma to separate the two sentences. This is a common punctuation mistake.

• I want to pass the test. Therefore, I work hard. OR I want to pass the test; therefore, I work hard. (BUT NOT I want to pass the test, therefore, I work hard.)