Here's a breakdown:
1. Coordinating Conjunctions (FANBOYS):
* For, And, Nor, But, Or, Yet, So
* Rule: Use a comma before a coordinating conjunction only when it joins two independent clauses.
* Independent clause: A complete sentence with a subject and a verb.
Examples:
* Correct: I went to the store, and I bought some groceries.
* Incorrect: I went to the store and bought some groceries. (No comma needed because "bought some groceries" is not an independent clause)
2. Subordinating Conjunctions:
* Examples: because, although, since, while, if, unless, before, after, etc.
* Rule: You generally do not use a comma before a subordinating conjunction.
* Exception: When the dependent clause comes before the independent clause, you do use a comma.
Examples:
* Correct: I went to the store because I needed milk. (Dependent clause comes after independent clause)
* Correct: Because I needed milk, I went to the store. (Dependent clause comes before independent clause)
3. Conjunctive Adverbs:
* Examples: however, therefore, nevertheless, moreover, consequently, etc.
* Rule: You always use a comma before and after a conjunctive adverb.
Examples:
* Correct: I went to the store; however, they were out of milk.
* Correct: I went to the store. Therefore, I had to go to another one.
Remember: These are just general guidelines. There are exceptions and nuances in specific cases. If you're unsure, it's always a good idea to consult a style guide or a grammar textbook for clarification.