Commas

A comma can be used to indicate a pause in speech, or a break in the conversation. These do not signify the end of a sentence, but they can often signify the point where a person needs a break, or it can show where the focus of a sentence is changing, when you have a situation in which the subject can stay the same, but the focus of the sentence is changing slightly. A comma can be a very useful tool in writing, but it can also cause a lot of mistakes, as in the case of a comma splice. This is a situation in which you have a long, run-on sentence, and the writer chose to "fix" it by adding a comma in place of a period or a semicolon. In this situation, the best thing to do (if you are the writer) is to definitely try to read the sentence aloud. If it sounds unnatural, or you seem to be addressing more than one major point, then you will probably have a comma splice, and need to fix it. You can definitely have a case of too many commas, if you aren't careful.