not so much agreed what is the standard of the internal nature of man as of his external form. Neither is this last exactly settled. Yet we understand one another when we speak of the shape of a human body: so likewise we do when we speak of the heart and inward principles, how far soever the standard is from being exact or precisely fixed. There is therefore ground for an attempt of showing men to themselves, of showing them what course of life and behaviour their real nature points out and would lead them to. Now obligations of virtue shown, and motives to the practice of it enforced, from a review of the nature of man, are to be considered as an appeal to each particular person's heart and natural conscience: as the external senses are appealed to for the proof of things cognisable by them. Since, then, our inward feelings, and the perceptions we receive from our external senses, are equally real, to argue from the former to life and conduct is as little liable to exception as to argue from the latter to absolute speculative truth. A man can as little doubt whether his eyes were given him to see with as he can doubt of the truth of the science of _optics_, deduced from ocular experiments. And allowing the inward feeling, shame, a man can as little doubt whether it was given him to prevent his doing shameful actions as he can doubt whether his eyes were given him to guide his steps. And as to these inward feelings themselves, that they are real, that man has in his nature passions and affections, can no more be questioned than that he has external senses. Neither can the former be wholly mistaken, though to a certain degree liable to greater mistakes than the latter. There can be no doubt but that several propensions or instincts, several principles in the heart of man, carry him to society, and to contribute to the happiness of it, in a sense and a manner in which no inward principle leads him to evil. These principles, propensions, or instincts which lead him to do good are approved of by a certain faculty within, quite distinct from these propensions themselves. All this hath been fully made out in the foregoing discourse.