After all that has been said by metaphysicians about the existence and seat of the moral sense, I think I can solve every difficulty by a new theory. You know some philosophers suppose the moral sense to be intuitive and inherent in man: others who deny the doctrine of innate ideas, treat this notion of innate sentiments as equally absurd. There they certainly are wrong, for sentiments are widely different from ideas, and I have that within me which convinces my understanding that sentiments must be innate, and proportioned to the delicacy of our sensibility; no person of common sense or feeling can doubt this. But there are other points which I own puzzled me till yesterday: some metaphysicians would seat the moral sense inherently in the heart, others would place it intuitively in the brain, all would confine it to the soul; now in my opinion it resides primarily and principally in the nerves, and varies with their variations. Hence the difficulty of making the moral sense a universal guide of action, since it not only differs in many individuals, but in the same persons at different periods of their existence, or (as I have often experienced) at different hours of the day. All this must depend upon the mobility of the nervous system: upon this may _hinge_ the great difficulties which have puzzled metaphysicians respecting consciousness, identity, &c. If they had attended less to the nature of the soul, and more to the system of the nerves, they would have avoided innumerable errors, and probably would have made incalculably important discoveries. Nothing is wanting but some great German genius to bring this idea of a moral sense in the nerves into fashion. Indeed, if our friend Mad. ---- would mention it in the notes to her new novel, it would introduce it, in the most satisfactory manner possible, to all the fashionable world abroad; and we take our notions in this country implicitly from the continent. As for you, my dear Gabrielle, I know you cut the Gordian knot at once, by referring, with your favourite moralist, every principle of human nature to self-love. This does not quite accord with my ideas; there is something harsh in it that is repugnant to my sensibility; but you have a stronger mind than I have, and perhaps your theory is right.