A RUN-ON sentence is a sentence that joins two independent clauses without punctuation or the appropriate conjunction. 
For example, “James is quite intelligent he began playing chess when he was two years old.”

A COMMA SPLICE is similar to a run-on sentence, but it uses a comma to join two independent clauses.
For example, “James is quite intelligent, he began playing chess when he was two years old.”

Fixing a run-on sentence or a comma splice can be accomplished in one of five different ways:

1) Separate the clauses into two sentences.
2) Replace the comma with a semi-colon.
3) Replace the comma with a coordinating conjunction (i.e., and, but, for, or, yet, nor, so.)
4) Use the comma with a subordinating conjunction (i.e., after, although, before, unless, as, because, even though, if, since, until, when, while, etc.)
5) Replace the comma with a semi-colon and transitional word (i.e., however, moreover, on the other hand, nevertheless, instead, also, therefore, consequently, otherwise, as a result, etc.)

Let’s look again at the incorrect sentences and then use each of the five ways to fix them.

INCORRECT:
“James is quite intelligent he began playing chess when he was two years old.”
“James is quite intelligent, he began playing chess when he was two years old.”

Correct: “James is quite intelligent. He began playing chess when he was two years old.” (Method #1)
Correct: “James is quite intelligent; he began playing chess when he was two years old.” (Method #2)
Correct: “James is quite intelligent and he began playing chess when he was two years old.” (Method #3)
Correct: “Because James is quite intelligent, he began playing chess when he was two years old.” (Method #4)
Correct: “James is quite intelligent; as a result, he began playing chess when he was two years old.” (Method #5)

Pay attention to your writing and make sure that your independent clauses are properly taken care of. Learn to avoid run-ons and comma splices in your writing, and you’ll be as smart as James.