For when the Gentiles, which have not the law, do by nature the things contained in the law, these having not the law, are a law unto themselves.
As speculative truth admits of different kinds of proof, so likewise moral obligations may be shown by different methods. If the real nature of any creature leads him, and is adapted to such and such purposes only, or more than to any other; this is a reason to believe the Author of that nature intended it for those purposes. Thus there is no doubt the eye was intended for us to see with. And the more complex any constitution is, and the greater variety of parts there are which thus tend to some one end, the stronger is the proof that such end was designed. However, when the inward frame of man is considered as any guide in morals, the utmost caution must be used that none make peculiarities in their own temper, or any thing which is the effect of particular customs, though observable in several, the standard of what is common to the species; and, above all, that the highest principle be not forgot or excluded, that to which belongs the adjustment and correction of all other inward movements and affections: which principle will of course have some influence, but which, being in nature supreme, as shall now be shown, ought to preside over and govern all the rest. The difficulty of rightly observing the two former cautions the appearance there is of some small diversity amongst mankind with respect to this faculty, with respect to their natural sense of moral good and evil; and the attention.. necessary to survey with any exactness what passes within have occasioned that it is 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 cognizable 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 occular 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.
But it may be said, "What is all this, though true, to the purpose of virtue and religion? these require, not only that we do good to others when we are led this way, by benevolence or reflection happening to be stronger than other principles, passions, or appetites; but likewise that the whole character be formed upon thought and reflection; that every action be directed by some determinate rule, some other rule than the strength and prevalency of any principle or passion. What sign is there in our nature (for the inquiry is only about what is collected from thence) that this was intended by its Author? or how does so various and fickle a temper as that of man appear adapted thereto? It may indeed be absurd and unnatural for men to act without any reflection; nay without regard to that particular kind of reflection which you call conscience; because this does belong to our nature. For, as there never was a man but who approved one place, prospect, building, before another; so it does not appear that there ever was a man who would not have approved an action of humanity rather than of cruelty; interest and passion being quite out of the case. But interest and passion do come in, and are often too strong for, and prevail over reflection and conscience. Now, as brutes have various instincts, by which they are carried on to the end the Author of their nature intended them for; is not man in the same condition, with this difference only, that to his instincts (i. e. appetites and passions) is added the principle of reflection or conscience? And as brutes act agreeably to their nature, in following that principle or particular instinct which for the present is strongest in them; does not man likewise act agreeably to his nature, or obey the law of his creation, by following that principle, be it passion or conscience, which for the present happens to be strongest in him? Thus, different men are by their particular nature hurried on to pursue honor, or riches, or pleasure. There are also persons whose temper leads them in an uncommon degree to kindness, compassion, doing good to their fellow creatures; as there are others who are given to suspend their judgment, to weigh and consider things, and to act upon thought and reflection. Let everyone then quietly follow his nature; as passion, reflection, appetite, the several parts of it, happen to the strongest; but let not the man of virtue take upon him to blame the ambitious, the covetous, the dissolute; since these, equally with him, obey and follow their nature. Thus, as in some cases, we follow our nature in doing the works contained in the law, so in other cases we follow nature in doing contrary."
Now, all this licentious talk entirely goes upon a supposition, that men follow their nature in the same sense, in violating the known rules of justice and honesty for the sake of a present gratification, as they do in following those rules when they have no temptation to the contrary. And if this were true, that could not be so which St Paul asserts, that men are "by nature a law to themselves." If by following nature were meant only acting as we please, it would indeed be ridiculous to speak of nature as any guide in morals: nay, the very mention of deviating from nature would be absurd; and the mention of following it, when spoken by way of distinction, would absolutely have no meaning. For, did ever anyone act otherwise than as he pleased? And yet the ancients speak of deviating from nature, as vice: and of following nature so much as a distinction, that, according to them, the perfection of virtue consists therein. So that language itself should teach people another sense to the words following nature, than barely acting as we please. Let it however be observed, that though the words human nature are to be explained, yet the real question of this discourse is not concerning the meaning of words, any otherwise than as the explanation of them may be needful to make out and explain the assertion, that every man if naturally a law to himself; that everyone may find within himself the role of right, and obligations to follow it. This St Paul affirms in the words of the text, and this the foregoing objection really denies, by seeming to allow it. And the objection will be fully answered, and the text before us explained, by observing, that nature is considered in different views, and the word used in different senses; and by showing in what view it is considered, and in what sense the word is used, when intended to express and signify that which is the guide of life, that by which men are a law to themselves. I say, the explanation of the term will be sufficient, because from thence it will appear, that in some senses of the word nature cannot be, but that in another sense it manifestly is, a law to us.
I. By nature is often meant no more than some principle in man, without regard either to the kind or degree of it. Thus, the passion of anger, and the affection of parents to their children, would be called equally natural. And as the same person hath often contrary principles, which at the same time draw contrary ways, he may by the same action both follow and contradict his nature in this sense of the word; he may follow one passion, and contradict another.
II. Nature is frequently spoken of as consisting in those passions which are strongest, and most influence the actions; which being vicious ones, mankind is in this sense naturally vicious, or vicious by nature. Thus St Paul says of the Gentiles, who were dead in trespasses and sins, and walked according to the spirit of disobedience, that they were by nature the children of Wrath. 
They could be no otherwise children of wrath by nature, than they were vicious by nature.
Here then are two different senses of the word nature, in neither of which men can at all be said to be a law to themselves. They are mentioned only to be excluded; to prevent their being confounded, as the latter is in the objection, with another sense of it, which is now to be inquired after and explained.
III. The apostle asserts, that the Gentiles do by nature the things contained in the law. Nature is indeed here put by way of distinction from revelation, but yet it is not a mere negative. He intends to express more than that by which they did not, that by which they did the works of the law; namely, by nature. It is plain the meaning of the word is not the same in this passage as in the former, where it is spoken of as evil; for in this latter it is spoken of as good; as that by which they acted, or might have acted virtuously. What that is in man by which he is naturally a law to himself; is explained in the following words: Which shows the work of the law, written in their hearts, their consciences also bearing witness, and their thoughts the meanwhile accusing or else excusing one another. If there be a distinction to be made between the works written in their hearts, and the witness of conscience; by the former must be meant, the natural disposition to kindness and compassion, to do what is of good report, to which this apostle often refers; that part of the nature of man, treated of in the foregoing discourse, which, with very little reflection and of course, leads him to society, and by means of which he naturally acts a just and good part in it, unless other passions or interest lead him astray. Yet since other passions, and regards to private interest, which lead us (though indirectly, yet they lead us) astray, are themselves in a degree equally natural, and often most prevalent; and since we have no method or seeing the particular degrees in which one or the other is placed in us by nature, it is plain the former, considered merely as natural, good and right as they are, can no more be a law to us than the latter. But there is a superior principle of reflection or conscience in every man which distinguishes between the internal principles of his heart, as well as his external actions; which passes judgment upon himself and them; pronounces determinately some actions to be in themselves just, right, good; others to be in themselves evil, wrong, unjust: which, without being consulted, without being advised with, magisterially exerts itself, and approves or condemns him, the doer of them, accordingly; and which, if not forcibly stopped, naturally and always of course goes on to anticipate a higher and more effectual sentence, which shall hereafter second and affirm its own. But this part of the office of conscience is beyond my present design explicitly to consider. It is by this faculty, natural to man, that he is a moral agent, that he is a law to himself. By this faculty, I say, not to be considered merely as a principle in his heart, which is to have some influence as well as others; but considered as a faculty, in kind and in nature, supreme over all others, and which bears its own authority of being so.
This prerogative, this natural supremacy, of the faculty which surveys, approves, or disapproves the several affections of our mind, and actions of our lives, being that by which men are a law to themselves, their conformity or disobedience to which law of our nature renders their actions, in the highest and most proper sense, natural or unnatural; it is fit it be further explained to you: and I hope it will be so, if you will attend to the following reflections.
Man may act according to that principle or inclination which for the present happens to be strongest, and yet act in a way disproportionate to, and violate his real proper nature. Suppose a brute creature by any bait to be allured into a snare, by which he is destroyed: he plainly followed the bent of his nature, leading him to gratify his appetite. There is an entire correspondence between his whole nature and such an action: such action therefore is natural. But suppose a man, foreseeing the same danger of certain ruin, should rush into it for the sake of a present gratification; he in this instance would follow his strongest desire, as did the brute creature. But there would be as manifest a disproportion between the nature of a man and such an action, as between the meanest work of art and the skill of the greatest master in that art; which disproportion arises, not from considering the action singly in itself; or in its consequences, but from comparison of it with the nature of the agent. And since such an action is utterly disproportionate to the nature of man, it is in the strictest and most proper sense unnatural; this word expressing that disproportion. Therefore, instead of the words disproportionate to his nature, the word unnatural may now be put; this being more familiar to us: but let it be observed, that it stands for the same thing precisely.
Now, what is it which renders such a rash action unnatural? Is it that he went against the principle of reasonable and cool self-love, considered merely as a part of his nature? No: For if he had acted the contrary way, he would equally have gone against a principle, or towards, part of his nature, namely, passion or appetite. But, to deny a present appetite, from foresight that the gratification of it would end in immediate ruin or extreme misery, is by no means an unnatural action. Whereas, to contradict or go against cool self-love, for the sake of such gratification, is so in the instance before us. Such an action then being unnatural, and its being so not arising from a man's going against a principle or desire barely, nor in going against that principle or desire which happens for the present to be strongest; it necessarily follows, that there must be some other difference, or distinction, to be made between these two principles, passion and cool self-love, than what I have yet taken notice of. And this difference, not being a difference in strength or degree, I call a difference in nature and in kind. And since, in the instance still before us, if passion prevails over self-love, the consequent action is unnatural; but if self-love prevails over passion, the action is natural; it is manifest that self-love is in human nature a superior principle to passion. This may be contradicted without violating that nature, but the former cannot. So that, if we will act conformably to the economy of man's nature, reasonable self-love must govern. Thus, without particular consideration of conscience, we may have a clear conception of the superior nature of one inward principle to another; and see that there really is this natural superiority, quite distinct from degrees of strength and prevalency.
Let us now take a view of the nature of man, as consisting partly of various appetites, passions, affections, and partly of the principle of reflection or conscience; leaving quite out all consideration of the different degrees of strength, in which either of them prevail; and it will further appear, that there is this natural superiority of one inward principle to another, or that it is even part of the idea of reflection or conscience.
Passion or appetite implies a direct simple tendency towards such and such objects, without distinction of the means by which they are to be obtained. Consequently, it will often happen there will be a desire of particular objects, in cases where they cannot be obtained without manifest injury to others. Reflection, or conscience comes in, and disapproves the pursuit of them in these circumstances; but the desire remains. Which is to be obeyed, appetite or reflection? Cannot this question be answered from the economy and constitution of human nature merely, without saying which is strongest? or need this at all come into consideration? Would not the question be intelligibly and fully answered by saying, that the principle of reflection or conscience being compared with the various appetites, passions, and affections in men the former is manifestly superior and chief, without regard to strength? And how often soever the latter happens to prevail, it is mere usurpation. The former remains in nature and in kind its superior; and every instance of such prevalence of the latter, is an instance of breaking in upon, and violation of the constitution of man.
All this is no more than the distinction which every body is acquainted with, between mere power and authority: only, instead of being intended to express the difference between what is possible, and what is lawful in civil government, here it has been shown applicable to the several principles in the mind of man. Thus, that principle by which we survey, and either approve or disapprove our own heart, temper, and actions, is not only to be considered as what is in its turn to have some influence; which may be said of every passion, of the lowest appetites: but likewise as being superior; as from its very nature manifestly claiming superiority over all others; insomuch that you cannot form a notion of this faculty, conscience, without taking in judgment, direction, superintendency. This is a constituent part of the idea, that is, of the faculty itself: and to preside and govern, from the very economy and constitution of man, belongs to it. Had it strength, as it has right; had it power, as it has manifest authority, it would absolutely govern the world.
This gives us a further view of the nature of man; shows us what course of life we were made for; not only that our real nature leads us to be influenced in some degree by reflection and conscience, but likewise in what degree we are to be influenced by it, if we will fall in with, and act agreeably to the constitution of our nature: that this faculty was placed within to be our proper governor; to direct and regulate all under principles, passions, and motives of action. This is its right and office: thus sacred is its authority. And how often soever men violate and rebelliously refuse to submit to it, for supposed interest which they cannot otherwise obtain, or for the sake of passion which they cannot otherwise gratify; this makes no alteration as to the natural right, and office of conscience.
Let us now turn the whole matter another way, and suppose there was no such thing at all as this supremacy of conscience; that there was no distinction to be made between one inward principle and another, but only that of strength; and see what would be the consequence.
Consider then what is the latitude and compass of the actions of man with regard to himself, his fellow creatures, and the Supreme Being? What are their bounds, besides that of our natural power? With respect to the two first, they are plainly no other than these: no man seeks misery as such for himself; and no one provoked does mischief to another for its own sake. For in every degree within these bounds, mankind knowingly, from passion or wantonness, bring ruin and misery upon themselves and others: and impiety and profaneness, I mean, what every one would call so who believes the being of God, have absolutely no bounds at all. Men blaspheme the Author of nature, formally, and in words renounce their allegiance to their Creator. Put an instance then with respect to any one of these three. Though we should suppose profane swearing, and in general that kind of impiety now mentioned, to mean nothing, yet it implies wanton disregard and irreverence towards an infinite Being, our Creator; and is this as suitable to the nature of man, as reverence and dutiful submission of heart towards that Almighty Being? Or suppose a man guilty of parricide, with all the circumstances of cruelty which such an action can admit of: this action is done in consequence of its principle being for the present strongest: and if there be no difference between inward principles, but only that of strength; the strength being given, you have the whole nature of the man given, so far as it relates to this matter. The action plainly corresponds to the principle, the principle being in that degree of strength it was: it therefore corresponds to the whole nature of the man. Upon comparing the action and the whole nature, there arises no disproportion, there appears no unsuitableness between them. Thus the murder of a father and the nature of man correspond to each other, as the same nature and an act of filial duty. If there be no difference between inward principles, but only that of strength, we can make no distinction between these two actions, considered as the actions of such a creature, but in our coolest hours must approve or disapprove them equally: than which nothing can be reduced to a greater absurdity.