I. The being whose actions the law of nature professes to regulate, is man. It is on the knowledge of his nature that the science of his duty must be founded.[15] It is impossible to approach the threshold of moral philosophy, without a previous examination of the faculties and habits of the human mind. Let no reader be repelled from this examination, by the odious and terrible name of _metaphysics_; for it is, in truth, nothing more than the employment of good sense, in observing our own thoughts, feelings, and actions; and when the facts which are thus observed, are expressed as they ought to be, in plain language, it is, perhaps, above all other sciences, most on a level with the capacity and information of the generality of thinking men. When it is thus expressed, it requires no previous qualification, but a sound judgment, perfectly to comprehend it; and those who wrap it up in a technical and mysterious jargon, always give us strong reason to suspect that they are not philosophers but impostors. Whoever thoroughly understands such a science, must be able to teach it plainly to all men of common sense. The proposed course will therefore open with a very short, and, I hope, a very simple and intelligible account of the powers and operations of the human mind. By this plain statement of facts, it will not be difficult to decide many celebrated, though frivolous, and merely verbal controversies, which have long amused the leisure of the schools, and which owe both their fame and their existence to the ambiguous obscurity of scholastic language. It will, for example, only require an appeal to every man's experience, to prove that we often act purely from a regard to the happiness of others, and are therefore social beings; and it is not necessary to be a consummate judge of the deceptions of language, to despise the sophistical trifler, who tells us, that, because we experience a gratification in our benevolent actions, we are therefore exclusively and uniformly selfish. A correct examination of facts will lead us to discover that quality which is common to all virtuous actions, and which distinguishes them from those which are vicious and criminal. But we shall see that it is necessary for man to be governed not by his own transient and hasty opinion upon the tendency of every particular action, but by those fixed and unalterable rules, which are the joint result of the impartial judgment, the natural feelings, and the embodied experience of mankind. The authority of these rules is, indeed, founded only on their tendency to promote private and public welfare; but the morality of actions will appear solely to consist in their correspondence with the rule. By the help of this obvious distinction we shall vindicate a just theory, which, far from being modern, is, in fact, as ancient as philosophy, both from plausible objections, and from the odious imputation of supporting those absurd and monstrous systems which have been built upon it.