I was going to do a great, long thing on commas, but I decided it was too long, no matter how great. So, I'll just explain a bit about commas and independent clauses.
An independent clause is basically a sentence or part of a sentence that could be a sentence on its own. That is, it has a subject (noun) and predicate (verb). Here are some examples of independent clauses:
Duke leaped the fence. (subject: Duke; predicate: leaped the fence)Yes, 'Duke leaped the fence' is the independent clause in all four examples. It's the last two examples I want to talk about.
Despite his sore leg, Duke leaped the fence.
James found the gate, but Duke leaped the fence.
Duke leaped the fence, and Jeremy ran after him.
You see, 'James found the gate' is also an independent clause, as is 'Jeremy ran after him.' You see how these are all separate sentences on their own, with subjects and predicates of their own.
Look how I separated the independent clauses in those sentences: I used a comma and a conjunction (and, but).
When putting two independent clauses together in one sentence, you need both a comma and a conjunction.
If you only use the comma, it's called a comma splice, because you're splicing together two sentences with a comma:
Duke leaped the fence, Jeremy ran after him.This is not a good thing. Grammatically, it can get you whipped with a wet noodle (many grammarians can't hold anything heavier than a wet noodle.)
So, you don't want to leave the conjunction out of the picture.
You don't want to leave the comma out, either.
"Duke leaped the fence and Jeremy ran after him" is also incorrect. This form, though, would only get you criticized, as opposed to noodled.
There are two other forms of punctuation you can use to put these sentences together: the period and the semi-colon. I'll just show you examples here:
Duke leaped the fence. Jeremy ran after him.See? Using a period is easy - it makes two separate, simple sentences. However, sometimes the second sentence follows the first in meaning, as well as position, and you may want to contain both in one sentence. That's when you would use a semi-colon (or the conjunction/comma combination above):
Duke leaped the fence; Jeremy ran after him.Speaking of colons, did you know that March is also Colorectal Cancer Awareness Month? So get your butt checked, so your colon doesn't become a semi-colon! (Yes, I stole that joke from the National Library of Medicine. No, I will not apologize.)