Duty, he says, cannot be resolved into Interest. The language of mankind makes the two distinct. Disregard of our interest is folly; of honour, baseness. Honour is more than mere reputation, for it keeps us right when we are not seen. This principle of Honour (so-called by men of rank) is, in vulgar phrase, honesty, probity, virtue, conscience; in philosophical language, the moral sense, the moral faculty, rectitude.
The principle is universal in men grown up to years of understanding. Such a testimony as Hume's may be held decisive on the reality of moral distinctions. The ancient world recognized it in the leading terms, honestum and utile, &c.
The abstract notion of Duty is a relation between the action and the agent. It must be voluntary, and within the power of the agent. The opinion (or intention) of the agent gives the act its moral quality.
As to the Sense of Duty, Reid pronounces at once, without hesitation, and with very little examination, in favour of an original power or faculty, in other words, a Moral Sense. Intellectual judgments are judgments of the external senses; moral judgments result from an internal moral sense. The external senses give us our intellectual first principles; the moral sense our moral first principles. He is at pains to exemplify the deductive process in morals. It is a question of moral reasoning, Ought a man to have only one wife? The reasons are, the greater good of the family, and of society in general; but no reason can be given why we should prefer greater good; it is an intuition of the moral sense.
He sums up the chapter thus:—'That, by an original power of the mind, which we call conscience, or the moral faculty, we have the conceptions of right and wrong in human conduct, of merit and demerit, of duty and moral obligation, and our other moral conceptions; and that, by the same faculty, we perceive some things in human conduct to be right, and others to be wrong; that the first principles of morals are the dictates of this faculty; and that we have the same reason to rely upon those dictates, as upon the determinations of our senses, or of our other natural faculties.' Hamilton remarks that this theory virtually founds morality on intelligence.
Moral Approbation is the affection and esteem accompanying our judgment of a right moral act. This is in all cases pleasurable, but most so, when the act is our own. So, obversely, for Moral Disapprobation.
Regarding Conscience, Reid remarks, first, that like all other powers it comes to maturity by insensible degrees, and may be a subject of culture or education. He takes no note of the difficulty of determining what is primitive and what is acquired. Secondly, Conscience is peculiar to man; it is wanting in the brutes. Thirdly, it is evidently intended to be the director of our conduct; and fourthly, it is an Active power and an Intellectual power combined.
ESSAY IV. is OF THE LIBERTY OF MORAL AGENTS, which we pass by, having noticed it elsewhere. ESSAY V. is OF MORALS.