Front Page Titles (by Subject) § 4.: Of the Notion of Duty, Rectitude, Moral Obligation - Selections from the Scottish Philosophy of Common Sense
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§ 4.: Of the Notion of Duty, Rectitude, Moral Obligation - Thomas Reid, Selections from the Scottish Philosophy of Common Sense 
Selections from the Scottish Philosophy of Common Sense, edited, with an introduction by G.A. Johnston (Chicago: Open Court, 1915).
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Of the Notion of Duty, Rectitude, Moral Obligation
A being endowed with the animal principles of action only may be capable of being trained to certain purposes by discipline, as we see many brute-animals are, but would be altogether incapable of being governed by law.
The subject of law must have the conception of a general rule of conduct, which, without some degree of reason, he cannot have. He must likewise have a sufficient inducement to obey the law, even when his strongest animal desires draw him the contrary way.
This inducement may be a sense of interest, or a sense of duty, or both concurring.
These are the only principles I am able to conceive, which can reasonably induce a man to regulate all his actions according to a certain general rule or law. They may therefore be justly called the rational principles of action, since they can have no place but in a being endowed with reason, and since it is by them only that man is capable either of political or of moral government.
Without them human life would be like a ship at sea without hands, left to be carried by winds and tides as they happen. It belongs to the rational part of our nature to intend a certain port, as the end of the voyage of life; to take the advantage of winds and tides when they are favourable, and to bear up against them when they are unfavourable.
A sense of interest may induce us to do this, when a suitable reward is set before us. But there is a nobler principle in the constitution of man, which, in many cases, gives a clearer and more certain rule of conduct, than a regard merely to interest would give, and a principle, without which man would not be a moral agent.
A man is prudent when he consults his real interest; but he cannot be virtuous, if he has no regard to duty.
I proceed now to consider this regard to Duty as a rational principle of action in man, and as that principle alone by which he is capable either of virtue or vice.
I shall first offer some observations with regard to the general notion of duty, and its contrary, or of right and wrong in human conduct, and then consider, how we come to judge and determine certain things in human conduct to be right, and others to be wrong.
With regard to the notion or conception of Duty, I take it to be too simple to admit of a logical definition.
We can define it only by synonymous words or phrases, or by its properties and necessary concomitants, as when we say that it is what we ought to do—what is fair and honest—what is approvable—what every man professes to be the rule of his conduct—what all men praise—and, what is in itself laudable, though no man should praise it.
I observe, in the next place, That the notion of duty cannot be resolved into that of interest, or what is most for our happiness.
Every man may be satisfied of this who attends to his own conceptions, and the language of all mankind shews it. When I say, This is my interest, I mean one thing; when I say, It is my duty, I mean another thing. And, though the same course of action, when rightly understood, may be both my duty and my interest, the conceptions are very different. Both are reasonable motives to action, but quite distinct in their nature.
I presume it will be granted, that, in every man of real worth, there is a principle of honour, a regard to what is honourable or dishonourable, very distinct from a regard to his interest. It is folly in a man to disregard his interest, but to do what is dishonourable, is baseness. The first may move our pity, or, in some cases, our contempt; but the last provokes our indignation.
As these two principles are different in their nature, and not resolvable into one, so the principle of honour is evidently superior in dignity to that of interest.
No man would allow him to be a man of honour who should plead his interest to justify what he acknowledged to be dishonourable; but to sacrifice interest to honour never costs a blush.
It likewise will be allowed by every man of honour, that this principle is not to be resolved into a regard to our reputation among men, otherwise the man of honour would not deserve to be trusted in the dark. He would have no aversion to lie, or cheat, or play the coward, when he had no dread of being discovered.
I take it for granted, therefore, that every man of real honour feels an abhorrence of certain actions, because they are in themselves base, and feels an obligation to certain other actions, because they are in themselves what honour requires, and this independently of any consideration of interest or reputation.
This is an immediate moral obligation. This principle of honour, which is acknowledged by all men who pretend to character, is only another name for what we call a regard to duty, to rectitude, to propriety of conduct. It is a moral obligation which obliges a man to do certain things because they are right, and not to do other things because they are wrong.
Ask the man of honour why he thinks himself obliged to pay a debt of honour? The very question shocks him. To suppose that he needs any other inducement to do it but the principle of honour, is to suppose that he has no honour, no worth, and deserves no esteem.
There is, therefore, a principle in man, which, when he acts according to it, gives him a consciousness of worth, and, when he acts contrary to it, a sense of demerit.
From the varieties of education, of fashion, of prejudices, and of habits, men may differ much in opinion with regard to the extent of this principle, and of what it commands and forbids; but the notion of it, as far as it is carried, is the same in all. It is that which gives a man real worth, and is the object of moral approbation.
Men of rank call it honour, and too often confine it to certain virtues that are thought most essential to their rank. The vulgar call it honesty, probity, virtue, conscience. Philosophers have given it the names of the moral sense, the moral faculty, rectitude.
If we examine the abstract notion of Duty, or Moral Obligation, it appears to be neither any real quality of the action considered by itself, nor of the agent considered without respect to the action, but a certain relation between the one and the other.
When we say a man ought to do such a thing, the ought, which expresses the moral obligation, has a respect, on the one hand, to the person who ought; and, on the other, to the action which he ought to do. Those two correlates are essential to every moral obligation; take away either, and it has no existence. So that, if we seek the place of moral obligation among the categories, it belongs to the category of relation.
There are many relations of things, of which we have the most distinct conception, without being able to define them logically. Equality and proportion are relations between quantities, which every man understands, but no man can define.
Moral obligation is a relation of its own kind, which every man understands, but is, perhaps, too simple to admit of logical definition. Like all other relations, it may be changed or annihilated by a change in any of the two related things—I mean the agent or the action.
Perhaps it may not be improper to point out briefly the circumstances, both in the action and in the agent, which are necessary to constitute moral obligation. The universal agreement of men in these, shews that they have one and the same notion of it.
With regard to the action, it must be a voluntary action, or prestation of the person obliged, and not of another. There can be no moral obligation upon a man to be six feet high. Nor can I be under a moral obligation that another person should do such a thing. His actions must be imputed to himself, and mine only to me, either for praise or blame.
I need hardly mention, that a person can be under a moral obligation, only to things within the sphere of his natural power.
As to the party obliged, it is evident there can be no moral obligation upon an inanimate thing. To speak of moral obligation upon a stone or a tree is ridiculous, because it contradicts every man’s notion of moral obligation.
The person obliged must have understanding and will, and some degree of active power. He must not only have the natural faculty of understanding, but the means of knowing his obligation. An invincible ignorance of this destroys all moral obligation.
The opinion of the agent in doing the action gives it its moral denomination. If he does a materially good action, without any belief of its being good, but from some other principle, it is no good action in him. And if he does it with the belief of its being ill, it is ill in him.
Thus, if a man should give to his neighbour a potion which he really believes will poison him, but which, in the event, proves salutary, and does much good; in moral estimation, he is a poisoner, and not a benefactor.
These qualifications of the action and of the agent, in moral obligation, are self-evident; and the agreement of all men in them shews that all men have the same notion, and a distinct notion of moral obligation.
We are next to consider, how we learn to judge and determine, that this is right, and that is wrong.
The abstract notion of moral good and ill would be of no use to direct our life, if we had not the power of applying it to particular actions, and determining what is morally good, and what is morally ill.
Some philosophers, with whom I agree, ascribe this to an original power or faculty in man, which they call the Moral Sense, the Moral Faculty, Conscience.
In its dignity it is, without doubt, far superior to every other power of the mind; but there is this analogy between it and the external senses, That, as by them we have not only the original conceptions of the various qualities of bodies, but the original judgment that this body has such a quality, that such another; so by our moral faculty, we have both the original conceptions of right and wrong in conduct, of merit and demerit, and the original judgments that this conduct is right, that is wrong; that this character has worth, that demerit.
The testimony of our moral faculty, like that of the external senses, is the testimony of nature, and we have the same reason to rely upon it.
The truths immediately testified by the external senses are the first principles from which we reason, with regard to the material world, and from which all our knowledge of it is deduced.
The truths immediately testified by our moral faculty, are the first principles of all moral reasoning, from which all our knowledge of our duty must be deduced.
By moral reasoning, I understand all reasoning that is brought to prove that such conduct is right, and deserving of moral approbation; or that it is wrong; or that it is indifferent, and, in itself, neither morally good nor ill.
I think, all we can properly call moral judgments, are reducible to one or other of these, as all human actions, considered in a moral view, are either good, or bad, or indifferent.
I know the term moral reasoning is often used by good writers in a more extensive sense; but, as the reasoning I now speak of is of a peculiar kind, distinct from all others, and, therefore, ought to have a distinct name, I take the liberty to limit the name of moral reasoning to this kind.
Let it be understood, therefore, that in the reasoning I call moral, the conclusion always is, That something in the conduct of moral agents is good or bad, in a greater or a less degree, or indifferent.
All reasoning must be grounded on first principles. This holds in moral reasoning, as in all other kinds. There must, therefore, be in morals, as in all other sciences, first or self-evident principles, on which all moral reasoning is grounded, and on which it ultimately rests. From such self-evident principles, conclusions may be drawn synthetically with regard to the moral conduct of life; and particular duties or virtues may be traced back to such principles, analytically. But, without such principles, we can no more establish any conclusion in morals, than we can build a castle in the air, without any foundation.1
[1 ]Ibid., pp. 586-590.