When to use a comma.

 

Introductory elements often require a comma, BUT not always

Commas are needed….

After an introductory clause

After a long introductory prepositional phrase or more than one introductory prepositional phrase

After introductory verbal phrases

If there is a distinct pause.

Some introductory elements don't require a comma

Sometimes the subject of a sentence looks like an introductory element… but isn't

Do not use a comma in the following cases:

After a brief prepositional phrase

After a restrictive appositive phrase

To separate the subject from the predicate

 

Tricky examples:

Preparing and submitting his report to the committee for evaluation and possible publication[,] was one of the most difficult tasks Bill had ever attempted.

To start a new business without doing market research and long-term planning in advance[,] would be foolish.

Extracting the most profit for the least expenditure on labor and materials[,] is the primary goal of a capitalist.

 

More info about the comma:

After introductory clauses, phrases, or words that come before the main clause

Common starter words: after, although, as, because, if, since, when, while

Examples:

While I was eating, the cat scratched at the door.

Because her alarm clock was broken, she was late for class.

If you are ill, you ought to see a doctor.

When the snow stops falling, we'll shovel the driveway.

 

In a compound sentence: A compound sentence is a sentence that has 2 independent clauses. An independent clause is a group of words with a subject and verb that expresses a complete thought.

            In a compound sentence we use comma before: and, but, or, nor, for, so, or yet to join two independent clauses that form a compound sentence.

            Example:

            -Linda ate a hamburger, but her friend played basketball.

            -John talked to the professor, and he agreed with him.

 

Attention! The compound sentence has to have two independent clauses, if not that will not work.

 For example:

Alpha read the paper but didn’t agree with the thesis.

In that sentence we don’t have any comma because the sentence after “but” is not an independent clause. If we want to have a comma we say:

 Alpha read the paper, but he didn’t agree with the thesis

 

In a complex sentence: A complex sentence is sentences that have one independent clause and one dependent clause joined together.

In a complex sentence we use a comma after a dependent clause which is preceded by a dependent marker.

Examples of dependent marker: because, before, since, while, although, if, until, when, after, as, as if.

Here is an example of a complex sentence which has a comma:

- Because doctors are concerned about the rising death rate from asthma, they have called for more research into its causes.