Some writers may write sentences that contain two complete ideas, punctuated only with a comma or with no punctuation at all. Both are wrong.
A complete sentence (also known as an independent clause) is a sentence that can stand on its own.
A "run-on sentence," or a "comma splice," occurs when two complete sentences are written together with no punctuation or with only a comma to separate them.
She walked the dog he fed the cat.
She walked the dog, he fed the cat.
I’ve always wanted to go to Reno it’s wonderful there.
I’ve always wanted to go to Reno, it’s wonderful there.
My father designs and installs wind turbines he travels all over Saudi Arabia as an energy consultant.
Notice that we have two ideas in two independent clauses:
My father installs and designs wind turbines.
He travels all over Saudi Arabia as an energy consultant.
To fix a run-on sentence, determine where one MAIN IDEA ends and another one begins.
1. Insert a period to make the two complete sentences separate.
She walked the dog. He fed the cat.
2. Insert a semicolon. Only use a semicolon if the two sentences are closely related.
I’ve always wanted to go to Reno; it’s wonderful there.
3. Add a word such as “and” or “therefore” after inserting a comma or a semicolon.
These words will need a comma before the word: and, but, for, or, nor, yet, so. Words such as “however,” “nevertheless,” “therefore,” “finally,” etc. will need a semicolon and a comma.
She walked the dog, and he fed the cat.
I’ve always wanted to go to Reno; however, I haven’t gone yet.