Method 3: Use a semicolon
Replace the comma with a semicolon.

Please note that this method should only be used when the two independent clauses (complete sentences) are closely related to each other or when the second clause expands on the reasoning of the first clause.

Mary wanted to cook a gourmet dinner for Bob; she signed up for cooking lessons.

Method 4: Use a semicolon with a conjunctive adverb
Place a semicolon after the first independent clause (complete sentence) followed by a conjunctive adverb (e.g., however, therefore, meanwhile, nevertheless) and a comma.

Please note that when a conjunctive adverb connects two independent clauses, it is preceded by a semicolon and followed by a comma.

Mary wanted to cook a gourmet dinner for Bob; therefore, she signed up for cooking lessons.

Method 5: Make one of the independent clauses a subordinate (dependent) clause
A subordinating conjunction (e.g., after, as, because, even though, since, when, while) can be used to change one of the independent clauses (complete sentences) to a subordinate (dependent) clause.

Please note that this may sometimes require moving and slightly changing the independent clauses.

If the subordinate clause comes first, it must be followed by a comma. When the independent clause comes first, there is no comma between the independent clause and subordinate clause.

Since Mary wanted to cook a gourmet dinner for Bob, she signed up for cooking lessons.

Mary signed up for cooking lessons because she wanted to cook a gourmet dinner for Bob.

A Final Note on Comma Splices

There’s one question I know someone will want to ask, so I’ll do it for you.

Is it ever okay to use a comma splice?

There are arguments for stylistic choices. Some authors claim the comma splice lends a more poetic feel to their writing. Most notably, Cormac McCarthy uses comma splices for stylistic reasons.

Authors who write in a stream-of-consciousness style (e.g., James Joyce, Virginia Woolf) use comma splices to relate a character’s thoughts, feelings, and reactions in a continuous flow uninterrupted by objective description or conventional dialogue.

While comma splices may work as a stylistic choice for some authors, including those mentioned above, it won’t work for every author.

The most common “accepted” stylistic use of comma splices in fiction writing is in dialogue. A comma splice in dialogue can be used to convey heightened emotion and/or a character who rushes their words out without taking a breath (or coming to a full stop) between sentences.