I'm probably asking this because I still have a lot to learn about writing. Anyway, apparently, this is allowed: "He's cool, but he's not as cool as she is." But this isn't allowed: "He's cool, but not as cool as she is." You're not allowed to place commas before a conjunction if the second clause isn't independent. First of all, it'd be great if somebody could confirm this. Let's assume the rule is correct. The thing is, I see this rule broken in novels all the time. But I keep asking myself if it's really that important? It doesn't distract or confuse me. Isn't that the most important thing in writing? To keep things clear and not confusing. I'm asking this because I'd like to respect grammar, but I don't want to be restricted by it. Thank you for sharing your insightful thoughts.