1. "So" as a coordinating conjunction:
* No comma needed: When "so" connects two independent clauses, it functions as a coordinating conjunction like "and", "but", or "or". In this case, you don't need a comma.
* Example: "I was tired, so I went to bed early."
2. "So" introducing an adverbial clause:
* Comma needed: When "so" introduces a dependent clause that modifies the main clause, it functions as a conjunction introducing an adverbial clause. You generally need a comma before "so".
* Example: "I was tired, so I decided to take a nap." (The clause "so I decided to take a nap" explains why the speaker was tired.)
3. "So" introducing a result clause:
* Comma optional: Sometimes, "so" introduces a clause that expresses the result of a previous statement. In this case, the comma is optional, depending on the length and complexity of the sentence.
* Example: "I was very busy, so I didn't have time to go to the store." (Comma optional)
4. "So" as an intensifier:
* No comma needed: When "so" intensifies an adjective or adverb, it doesn't introduce a clause, so no comma is needed.
* Example: "I was so tired that I fell asleep."
In summary:
* Use a comma before "so" when it introduces an adverbial clause (explains why or how something happens).
* Don't use a comma before "so" when it connects two independent clauses or acts as an intensifier.
* In result clauses, the comma is optional based on sentence structure.
If you're unsure whether to use a comma, try reading the sentence aloud. If you naturally pause before "so", a comma is likely needed.