1. Find the subjects and verbs of the sentence.

2. Identify whether each subject and verb belongs to an independent or a dependent clause.

Independent clauses:

Jasper was a birdwatcher.

Juanita enjoyed stargazing.

Dependent clauses:

Since Jasper was a birdwatcher

When Juanita enjoyed stargazing

3. If you find two independent clauses joined by a comma in the same sentence, draw an imaginary line between them.
Jasper was a birdwatcher, | Juanita enjoyed stargazing.

4. Fix the comma splice in one of these ways:

a. Separate the independent clauses with a period or a semicolon.
Correct: Jasper was a birdwatcher; Juanita enjoyed stargazing.

b. Use a comma before a coordinating conjunction: and, or, nor, but, for, so, yet.
Correct: Jasper was a birdwatcher, but Juanita enjoyed stargazing.

1. Use a comma after a long introductory subordinate clause. A subordinate clause is a unit that contains a subject and verb and is introduced by a subordinating conjunction such as after, although, because, if, since, though, when, or where.

Example: Although the United States once employed hundreds of lighthouse

The main clause in this sentence is today there are only two. The rest of the material leading up to the main clause is an introductory subordinate clause and should be set off with a comma.

Revised: Although the United States once employed hundreds of lighthouse keepers, today there are only two.

2. Use a comma after longer introductory adverbial phrases. An introductory phrase of more than five words should be set off from the main clause by a comma. Often these phrases will begin with a preposition such as after, at, between, for, in, over, through, or until.

Example: Between the piers of the harbor two automated lighthouses guide ships during the night.

The main clause of this sentence, two automated lighthouses guide ships during the night, is introduced by a long adverbial phrase. The introductory phrase needs to be set off by a comma.

Revised: Between the piers of the harbor, two automated lighthouses guide ships during the night.

3. Shorter introductory phrases generally do not need to be set off by a comma.

Example: On Thursday a ship ran aground in the harbor.

However, a comma should be used if it will help to clarify meaning or prevent a misreading.

Example: To many sailors seem to lead an exotic, independent life.

Here it is easy to misread sailors as part of the introductory phrase. This misreading can be prevented by putting a comma after the introductory phrase.

Revised: To many, sailors seem to lead an exotic, independent life.

1. Find the clause beginning with that or which. If the clause begins with a that, omit the comma. If the clause begins with a which, continue to step 2.

a. Example of "that" clause: The only way that Fred could determine the way home was by tracking the position of the sun.
b. Example of "which" clause: Fred found his way home by tracking the position of the sun, which was one of several methods he'd used in the past.

2. Figure out exactly what sentence element the which clause describes or modifies.

a. The solution for insomnia which seemed most promising to the students was listening to Professor Crabbe's lecture on sleep disorders.
b. One solution for insomnia, which seemed most promising to the students, was listening to Professor Crabbe's lecture on sleep disorders.

In both of these examples, the which clause describes Professor Crabbe's lecture on sleep disorders.

3. Ask yourself the following questions:

a. Is the clause necessary to understanding the sentence element it modifies?
b. Does the clause merely add information to, but not define, the sentence element it modifies?

In Example 2a above, which introduces something essential about Professor Crabbe's lecture. You can't really separate the "seemed most promising to the students" part from the rest of the sentence without fundamentally changing the meaning of the sentence.

In Example 2b, the commas that mark off the which clause serve almost the same purpose as parentheses: they bracket a clause that brings additional, nonessential information to the sentence. Here, what the students thought about the lecture does not define it.

4. If the which clause is necessary to understanding the sentence element, do not use a comma. If the which clause merely adds information about the element but does not define it, insert a comma before which and, if the clause does not end the sentence, after the clause.

1. Use a comma after a "because" clause, placed before the main clause.

Example: Because the owner was arrested for embezzling retirement funds the company's stock fell.

Here the main clause is the company's stock fell. A comma is needed after the because clause at the beginning of the sentence

Revised: Because the owner was arrested for embezzling retirement funds, the company's stock fell.

2. Do not use a comma before a "because" clause that follows a main clause.

Example: The company's stock fell, because the owner was arrested for embezzling retirement funds.

Here the main clause (The company's stock fell) begins the sentence. No comma is needed between the main clause and the "because" clause that follows it.

Revised: The company's stock fell because the owner was arrested for embezzling retirement funds.