Having with wary steps traced an intricate road, not without danger of wandering; what remains to complete our journey, is to account for the final cause of congruity and propriety, which make so great a figure in the human constitution. One final cause, regarding congruity, is pretty obvious. The sense of congruity, as one of the principles of the fine arts, contributes in a remarkable degree to our entertainment. This is the final cause assigned above for our sense of proportion[6], and need not be enlarged upon here. Congruity indeed with respect to quantity, coincides with proportion. When the parts of a building are nicely adjusted to each other, it may be said indifferently, that it is agreeable by the congruity of its parts, or by the proportion of its parts. But propriety, which regards voluntary agents only, can never in any instance be the same with proportion. A very long nose is disproportioned, but cannot be termed _improper_. In some instances, it is true, impropriety coincides with disproportion in the same subject, but never in the same respect. I give for an example a very little man buckled to a long toledo. Considering the man and the sword with respect to size, we perceive a disproportion. Considering the sword as the choice of the man, we perceive an impropriety.
The sense of impropriety with respect to mistakes, blunders, and absurdities, is happily contrived for the good of mankind. In the spectators it is productive of mirth and laughter, excellent recreation in an interval from business. The benefit is still more extensive. It is not agreeable to be the subject of ridicule; and to punish with ridicule the man who is guilty of an absurdity, tends to put him more upon his guard in time coming. Thus even the most innocent blunder is not committed with impunity; because, were errors licensed where they do no hurt, inattention would grow into a habit, and be the occasion of much hurt.
The final cause of propriety as to moral duties, is of all the most illustrious. To have a just notion of it, the two sorts of moral duties must be kept in view, _viz._ those that respect others, and those that respect ourselves. Fidelity, gratitude, and the forbearing injury, are examples of the first sort; temperance, modesty, firmness of mind, are examples of the other. The former are made duties by means of the moral sense; the latter, by means of the sense of propriety. Here is a final cause of the sense of propriety, that must rouse our attention. It is undoubtedly the interest of every man, to regulate his behaviour suitably to the dignity of his nature, and to the station allotted him by Providence. Such rational conduct contributes in every respect to happiness: it contributes to health and plenty: it gains the esteem of others: and, which is of all the greatest blessing, it gains a justly-founded self-esteem. But in a matter so essential to our well-being, even self-interest is not relied on. The sense of propriety superadds the powerful authority of duty to the motive of interest. The God of nature, in all things essential to our happiness, hath observed one uniform method. To keep us steady in our conduct, he hath fortified us with natural principles and feelings. These prevent many aberrations, which would daily happen were we totally surrendered to so fallible a guide as is human reason. The sense of propriety cannot justly be considered in another light, than as the natural law that regulates our conduct with respect to ourselves; as the sense of justice is the natural law that regulates our conduct with respect to others. I call the sense of propriety a law, because it really is so, not less than the sense of justice. If by law be meant a rule of conduct that we are conscious ought to be obeyed, this definition, which I conceive to be strictly accurate, is applicable undoubtedly to both. The sense of propriety includes this consciousness; for to say an action is proper, is, in other words, to say, that it _ought_ to be performed; and to say it is improper, is, in other words, to say, that it _ought_ to be forborn. It is this very consciousness of _ought_ and _should_ included in the moral sense, that makes justice a law to us. This consciousness of duty, when applied to propriety, is perhaps not so vigorous or strong as when applied to justice: but the difference is in degree only, not in kind: and we ought, without hesitation or reluctance, to submit equally to the government of both.