I've always wondered about JA's use of 'gratitude'. I've found a possible source from Fanny Burney's Evelina. According to conduct-writer John Gregory, "What is commonly called love among you is rather gratitude, and a partiality to the man who prefers you to the rest of your sex;..this gratitude rises into a preference..If attachment was not excited in your sex in this manner, there is not one of a million of you that could ever marry with any degree of love."