"Is not this laid a little too strong? I desire your opinion of it, though I cannot entirely promise to conform myself to it. I wish from my heart I could avoid concluding, that since morality, according to your opinion, as well as mine, is determined merely by sentiment, it regards only human nature and human life. This has been often urged against you, and the consequences are very momentous. If you make any alterations in your performances, I can assure you, there are many who desire you would more fully consider this point, if you think that the truth lies on the popular side. Otherwise common prudence, your character, and situation, forbid you [to] touch upon it. If morality were determined by reason, that is the same to all rational beings; but nothing but experience can assure us that the sentiments are the same. What experience have we with regard to superior beings? How can we ascribe to them any sentiments at all? They have implanted those sentiments in us for the conduct of life like our bodily sensations, which they possess not themselves. I expect no answer to these difficulties in the compass of a letter. 'Tis enough if you have patience to read so long a letter as this.--I am." &c. The third volume of the "Treatise of Human Nature" being the part relating to morals, was published by Thomas Longman in 1740. It is not so original as the metaphysical part of the work, nor are its principles so clearly and decidedly laid down. Its author's metaphysical theories were rather modified than confirmed in his subsequent works. But his opinions on ethical subjects, only indistinctly shadowed forth in his early work, were afterwards reduced to a more compact system, and were more clearly and fully set forth.