As part of a discussion on another subject in the company of a bunch of Villains (that post and its extensive discussion are well worth reading in their own right), Grim pointed out a David Hume claim known today as Hume's Guillotine, or the is-ought problem. The link, provided by Grim, presents a good summary of the question; it's also laid out, of course, in Part III, Section 1, "Moral Distinctions Not Derived from Reason," of Hume's A Treatise of Human Nature. Grim asked what I thought of the matter.
The short answer is that Hume was wrong.
This post attempts to show how.
The salient parts of Hume's argument, as concerns this post, are these:
He states his problem:
Now as perceptions resolve themselves into two kinds, viz. impressions and ideas, this distinction gives rise to a question, with which we shall open up our present enquiry concerning morals. WHETHER IT IS BY MEANS OF OUR IDEAS OR IMPRESSIONS WE DISTINGUISH BETWIXT VICE AND VIRTUE, AND PRONOUNCE AN ACTION BLAMEABLE OR PRAISEWORTHY? … In order, therefore, to judge of these systems, we need only consider, whether it be possible, from reason alone, to distinguish betwixt moral good and evil, or whether there must concur some other principles to enable us to make that distinction.
Hume then makes this claim:
Since morals, therefore, have an influence on the actions and affections [through opinions of injustice or through a sense of obligation], it follows, that they cannot be derived from reason; and that because reason alone, as we have already proved, can never have any such influence. Morals excite passions, and produce or prevent actions. Reason itself is utterly impotent in this particular. The rules of morality, therefore, are not conclusions of our reason.
Hume notes, of Reason:
Reason is the discovery of truth or falsehood. Truth or falsehood consists in an agreement or disagreement either to the real relations of ideas, or to real existence and matter of fact. Whatever, therefore, is not susceptible of this agreement or disagreement, is incapable of being true or false, and can never be an object of our reason.
with this about morals:
Now it is evident our passions, volitions, and actions, are not susceptible of any such agreement or disagreement; being original facts and realities, compleat in themselves, and implying no reference to other passions, volitions, and actions. It is impossible, therefore, they can be pronounced true or false, and be either contrary or conformable to reason.
An administrivium: Hume makes a distinction between Reason and moral, identifying the moral as a passion. For this post, I'll write about rational reason(ing) for Reason and moral reason(ing) for the moral.
Hume's proposition, itself, flows from a false dichotomy. Our reasoning and moral capacities are gifts from God—indeed, they are the same gift. The split between them is a wholly human-originated partition, which we generate strictly for the purpose of better understanding the gift. Thus, rational and moral reasoning begin (its) existence in us, not just inextricably intertwined, but as one and the same. We can move between them as easily as we can move from our front yard to our back.
With regard to a part of the second above, concerning the claimed inability for rational reasoning to motivate behavior, this also is wrong. Consider a game of poker (which, when I was actively playing it had no relation with gambling whatsoever). A coldly objective—rationally reasoned—assessment of my hand, of the hands of my fellow players, of their betting histories, and so on, takes me to executing a behavior: fold, call, or bet, with a subset under betting of adjusting the size of these bets. Each of these behaviors is originally motivated by a reasoned assessment the data at hand; moral reasoning has not entered into it at all. A couple more examples: a man has a pistol and confronts a home invader who holds a weapon to the man's wife, threatening to her unless the man complies with a demand. This is a highly emotionally charged situation, yet the man can—and a trained man does—observe the factors, sees the wife does not cover very much of the home invader, the range is short, the invader's weapon is not an immediately lethal one (a knife, perhaps, or the finger is not on the trigger), assesses his own marksmanship, and makes a decision to take his shot—or not. Rational reasoning has determined the shot; rational reasoning has motivated the action of shooting or holding fire. So it is in another wholly unemotional—dispassionate—activity, like driving: an action of taking this route, or that one, based on the purpose of the trip and the relative efficiencies of the two routes. Rational reasoning determines the action of the choosing of the route and spurs the driver to act on the choice.
In the fourth above, concerning morals, his claim is internally contradictory. If we can say that a passion, a moral, is originally true, originally a fact, then we have...in fact…identified it so. While we have not identified a falsifiable alternative, we have identified a truth, a fact. This, comports with rational reasoning: a truth has been discovered. In this case of origin, that a falsehood is not present to be discovered in no way invalidates the rationally reasoned discovery of the original truth. A agreement or disagreement (the third above) is simply the agreement/disagreement that this discovery is an original fact. Of course, a first principle—an original fact—cannot be proved from within its own logical system, but if Hume is correct, rational reasoning is separate from moral reasoning, and it is this separate logical system that has discovered the original fact—from without that other system.
Moreover, if the moral is always, of origin, true—a true fact, as it were—and rational reasoning can distinguish between the true and the false, then it is eminently possible for rational reasoning to recognize the moral, when it recognizes a particular truth. Nor does rational reasoning need to be a (the) source of good or evil, as Hume decries it for not being: it need only be able to recognize the two and distinguish between them—as it does with any truth or falsehood.
Hume also proceeds from a minor false dichotomy: that it is "possible, from reason alone..." or "…whether there must concur some other principles…." Yet this is not an either/or proposition; both can be in play. Moral vice and virtue—morality—can be discerned through rational reasoning, but doing so does not preclude the same distinction by moral reasoning: that is, a virtuous end can be developed by rational reason, and that same virtuous end can be developed by moral reason. In short, we can, from rational reason alone, distinguish betwixt moral good and evil, and we can make the same distinction from moral reasoning, also. And, just to dot the i and cross the t, rational reasoning remains fully capable of discerning non-moral truths and falsehoods, as well. A couple of examples from our Founding will illustrate.
A rational reasoning argument for an economic exchange between free men that improves both men's well-being might go something like this. Each man has something of value that the other wants. The two freely and of their own volition agree on a medium of exchange and a value of the objects desired, and they execute the exchange. As a result of that exchange, both men are better off: both have gained something of value that they did not have before, and neither has not given up anything of greater value in order to realize the gain. But this is a free market.
A moral reasoning argument for an economic exchange between free men (keeping in mind the free will He has imbued in us), equal in the eyes of God, might go something like this. Each man has something of value that the other wants. The two freely agree on a medium of exchange and a value of the objects desired, and they execute the exchange. Neither man has gained dominion over the other as a result of the exchange, and neither man has used dominion to force the other into an exchange to which he would not otherwise have agreed. As a result of that exchange, both men are better off: both have gained something of value that they did not have before, and neither has not given up anything of greater value in order to realize the gain. But this is a free market. And in both free markets, the increased well-being of the two men has facilitated their ability to satisfy other moral obligations: they have, for instance, more wherewithal with which to help those less fortunate than they.
The other example concerns a type of government. A rational reasoning argument for a government suited to preserving the freedom of men, vis., the freedom of exchange economy described above might go something like this. What sort of government will best preserve that sort of free market economy? One such is a government that leaves the people sovereign over that government, easily able to draw the government back when it becomes too overreaching. This would include, especially for large populations, an electively-oriented representative sort of government at a local level, and groupings of these local governments into a larger, still electively-oriented, representative government at a national level, where the power of the sovereign people is preserved, and so is the power of their more-or-less local governing jurisdictions. With another little fillip: divide the government into equal, competing sections so as to make it yet harder for that national government to accrete power to itself. But this is, roughly, a republican government.
A moral reasoning argument for a government suited to preventing some men from gaining dominion over the rest—and so of preserving the morally-derived free economy described above—might go something like this. What sort of government preserves the essential equality of men before God? One sort is a government that leaves the people sovereign over that government, and so directly responsible for their own behavior, rather than surrendering that obligation to another—rather than ceding dominion to the men populating that government. This would include, especially for large populations, an electively-oriented representative sort of government at a local level, and groupings of these local governments into a larger, still electively-oriented, representative government at a national level, where the power of the sovereign people is preserved, and so is the power of their more-or-less local governing jurisdictions. With another little fillip: divide the government into equal, competing sections so as to make it yet harder for that national government to gain dominion. The men of the governments at any level are thus prevented from gaining dominion over those whom they purport to represent. But this is, roughly, a republican government.
With these two examples, we see that rational reasoning and moral reasoning arrive at the same Reason and moral truths. Having achieved the crossover between Reason and moral at both endpoints, it's easy to see that the crossover can occur at any other place in the chain, as well.