The sentence above contains a dependent clause (a clause that cannot stand on its own as a complete grammatical sentence). Dependent clauses must be separated from the rest of the sentence, often using commas. This clause is also an introductory clause, and thus must be separated from the main clause with a comma after "dog." The best way to correct the sentence above is "While I was out walking my dog, it started to rain so hard I couldn't see."

Here, the phrase "my favorite food" is being used as an interrupting phrase, therefore it must be separated from the rest of the sentence with commas. "Cheese," the subject of the sentence, must be connected to the primary verb "is," so the interrupting phrase must be enclosed with commas, one on either end.

The full, correct version of the sentence reads: "Cheese, my favorite food, is the main reason I can never become a vegan."

There should be a comma after "ice cream" since this is a list of activities Martha would like to do. A list of three or more items should have a comma followed by an "and" right before the last item in the list.

Here, "finally" is considered an introductory word, so it must be followed by a comma: "Finally, the teacher . . ."

The list of "campers and their counselors" does not need a comma. Commas are only necessary in lists of three or more items, and this list only has two items. Therefore, "campers," must be changed. The use of a comma with the conjunction "and" signals a shift from one independent clause to another, which is not the case here.

Here, the phrase "my favorite food" is being used as an interrupting phrase, therefore it must be separated from the rest of the sentence with commas. "Cheese," the subject of the sentence, must be connected to the primary verb "is," so the interrupting phrase must be enclosed with commas, one on either end.

The full, correct version of the sentence reads: "Cheese, my favorite food, is the main reason I can never become a vegan."

This sentence features two independent clauses separated by a comma, otherwise known as a comma splice. The sentence needs to be separated by a conjunction like "and" or "so," or by a punctuation mark that divides the sentence into two, like a period or a semicolon.

This sentence is an example of a run-on or comma splice. It has two independent clauses separated only by a comma. One way to fix this is to change the comma to a semicolon; if this were to be done, the corrected sentence would read, "Thomas had always struggled with trigonometry; he thought that circles should remain circles and let triangles and squiggles be their own shapes."

There are several acceptable ways to separate independent clauses, but simply using a single comma by itself is not one of them. That is an error known as the comma splice. The three options available to correct such an error are a period, a conjunction with a comma, or a semicolon. These three options are all equally grammatically correct, which one you choose is a matter of style. The example sentence contains two independent clauses, so rather than a comma after "world" one of those three options needs to be inserted.

Two independent clauses being joined only by a single comma result in an error known as the "comma splice." In the example above, a period, a comma and a conjunction, or a semicolon would all be appropriate to punctuate the sentence.