A reader posted the following question: When can you use a comma to separate two independent clauses?
The answer: First, we at Syntaxis are impressed by your use of grammar terminology. An independent clause, for those who are unfamiliar with the term, is a group of words containing a subject and a verb, and capable of standing alone as a sentence.
Here are two independent clauses:
You could combine the clauses like this:
The oil company executives were questioned extensively, but their explanations were unsatisfactory.
But not like this:
The oil company executives were questioned extensively, their explanations were unsatisfactory.
The above sentence, with just a comma between the two clauses, is called a comma splice. That is not a good thing; it is considered an error. Think of the comma as being too dainty and delicate to hold apart two independent clauses without the assistance of a coordinating conjunction.
Some good news is that there are only seven such conjunctions, and you can use the mnemonic device (memory aid) fanboys to help you remember them.
A very common punctuation pattern is:
Here are two additional examples of that pattern:
Mark sent the report, and Jane called the client.
She needed some extra money, so she worked a lot of overtime.
Cautionary note: Do not use a comma before the "however" in the following example.
The oil company executives were questioned extensively; however, their explanations were unsatisfactory.
Note the semicolon. A comma in this position would be incorrect; it would once again create a comma splice, because you are essentially beginning what could be a new sentence. One alternative to the semicolon in this case would be a period:
The oil company executives were questioned extensively. However, their explanations were unsatisfactory.