[@KatherinWinter]
But according to the Fairy Tail lore they work differently. Also, someone correct me iff I'm wrong, but I'm pretty sure only demons use curses as well. If not it's very rare for anyone else to use curses. 

I also just read that curses run off of negative human emotion, like greed, envy, and hatred, while magic runs off of positive human emotions. So that is how they differ and only demons can use curses.