For Hume, no one could describe objective reasons for thinking that a man ought to do something generally, becuase there was no way to derive an ought from an is. But, if a classical view of causality (which Hume of course rejects) is introduced, for instance, the four causes of Aristotle, it seems like an ought can follow simply from an is. For Aristotle, final causality described what a thing is for. If we discern, for instance, that the human reproductive system is for procreation, then we have defined the final cause of the human reproductive system. Then, it seems to follow from the fact that the human reproductive system is for procreation that it ought to be used for procreation, and not in a way that is contrary to procreation, just as a knife is used to cut material, and not to stitch material back together again.

Have any authors responded to Hume's is/ought problem by invoking final causality?

  • It would shift the problem rather than solve it. It is unclear how we could possibly "discern" final causes (purposes) when all our perception can "discern" are facts. This is an even bigger problem than the ordinary "efficient" causality that we already cannot "discern", as Hume also pointed out, only postulate based on "constant conjunction". Postulating purposes does 'solve' the problem formally in the sense that one can then derive oughts from ises, but we cannot guarantee "objectivity" of such postulated purposes, as opposed to their pragmatic origin, say.
    – Conifold
    Aug 23, 2023 at 19:30

2 Answers 2


Hume was not, on his own terms, so dogmatic about the problem. He ends the oft-quoted passage about the is/ought gap by saying:

But as authors do not commonly use this precaution, I shall presume to recommend it to the readers; and am persuaded, that this small attention would subvert all the vulgar systems of morality, and let us see, that the distinction of vice and virtue is not founded merely on the relations of objects, nor is perceived by reason.

By themselves, these statements do not imply that deriving an "ought" from an "is" is absolutely impossible (Hume, as adventurously skeptical a thinker as he was, I would not expect to have come down so strictly on every conceivable such derivation; and there is a sense in which applying his own bundle-theory of objects generally, and particularly of subjective (human) objects, does mean adverting to relations between objects to characterize moral attitudes—but now we are speaking of either moral relations or relations-in-general trivially). We have, as a philosophical community, tended to extract a syntactic point from the appearance of the gap; then the naturalistic fallacy might be interpreted as the syntactic gap's semantic accompaniment.

Now, as for teleology, one question would be whether Thomistic ethics, say, is "vulgar" or not. Offhand, I assume not: Aquinas was a very elaborate and detailed theologian, who paired teleological with other normative judgments in representing his overarching system. If Aquinas had spoken with Hume, and if Hume had cautioned Aquinas about the is/ought gap, I expect that Aquinas could have easily responded with something like, "Then I will not use the word 'ought' [or rather, the Latin cognate] when it would cause my theory trouble to use it; the mere word 'ought' is not so important." (Actually, Aquinas would've put "on the contrary" in there somewhere, but nevermind that, I haven't read Aquinas' work enough to know his style the way I know Immanuel Kant's or John Rawls', say.)

Alternatively, taking Aquinas' system as bracketed on the lower end by the analytically justified imperative, "Do good and avoid evil," and on the upper end by, "The ultimate power of goodness in all possible reality has made our apprehension of Its presence into our ultimate goal," we can see that Aquinas both grounds, and diadems, his system with "oughts" that stand over the teleological semantics in play. For if God were not Good, say, then it would not do to claim that the beatific vision is justifiably promised unto us: the visio malefico de summum malum would hardly be what we "ought to aim for" even if Evil had created our souls and our world (if God were somehow Evil, then).

The upshot is that final causality is not really a synthetic bridge-principle over the gap: I can create a sword to kill, but it is not then that "the sword ought to kill" or even "I ought to use the sword to kill." If this were so, then it would not be that "is" and "ought" had been connected, but they would be conflated, which would suggest either equivocation or at least suppression-of-premises when it came to meaningful argument. At best, we might compare appeals-to-final-causality to prima facie duties/pro tanto reasons: something's-having-a-purpose might be a partial right/good-making property, but not enough to fully determine the rightness or goodness of fulfilling such a purpose.

If we want to apply this to questions of human sexuality, say, we might think:

  1. God predestined evolution to program sexual desires into humans so that humans would have a motive (pleasure) to engage in the bizarre ritual of conception.
  2. Some people were also predestined to be sexually attracted to others with whom they could not perform said ritual.
  3. Such people then have two purposes behind their sexual capacity: a general purpose based on reproduction and a particular purpose based on expression of romantic affection (for example).
  4. If they were to aim to fulfill only the one purpose, not only would they probably not fulfill it, but they would frustrate the other purpose.
  5. So why not permit them to fulfill the purpose that they can fulfill without feeling disgust and loneliness in return? If they are not, by doing so, frustrating other people's acceptable purposes, then doesn't the weight of teleological reasons favor said permission?

But I should observe, then, that this would be another possible problem with invoking final causality to bridge "is" and "ought": very well, you have gained the moral world, and now you can send your moral soul anywhere in that world, i.e. teleology is amorphous enough to be manipulated, as a premise, to trivially justify-or-condemn most anything under the sun. For example, if the sin in Eden recreated human nature with evil now internal to that nature, do we not have grounds to think that hatred of God is somehow part of our natural purpose, even if love is as well? Then the next problem is not triviality, but nullity: because we can be set contradictory purposes, even by God (let us suppose), then if some teleological "is" were enough to base a deontological "ought" upon, would we not end up losing the moral world, and our moral souls, to the void of inconsistent final causes?

We should not forget, either, that if a final cause really is a cause, then it really has an effect, and it doesn't have this effect contingent upon our will, but should override our will to guarantee that we act so as to fulfill the given purpose. Otherwise, a final cause is not a cause as a determinant of action but is yet an ideal for action, and then whether it is a justified ideal is no different a question than, "Is this ought-statement true?" in the first place.

  • 1
    The inconsistency is really a matter of what theology you put forward. If God is primarily good, and evil is only illusory or secondary, then so must be in humanity if they are to become God-like and achieve the ultimate telo. So you can postulate two telos but one that is primary and good and one that is secondary and evil. The fall from Eden was also a fall after all, away from the ultimate telo not towards it. But then who cares these days...
    – infatuated
    Aug 23, 2023 at 22:39
  • @infatuated my point is neither to affirm nor deny theocentric ethics, but to point out that a deontic reading of the divine nature in abstracto is still a matter of having a very substantive ought-like premise in place (to be precise, it is not the erogation, but the supererogation, operator that is in play in the grace of the divine will, here), with another sheer ought on the other end of the sequence of practical reasoning, "Do good and avoid evil." So for all this, the teleological premises do not suffice to constitutively justify themselves, but they are justified dependent on the Aug 24, 2023 at 0:02
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    @jaredad7 that does seem possible, in my eyes. I would rather not dismiss natural-law ethics altogether, anymore than I would want to dismiss utilitarianism or Kantianism or whatever (and neither Kant nor Rawls entirely dismissed the sense of natural moral laws, for that matter). If divine creation is ex nihilo whereas artifact creation (on our part) is rearrangement-of-matter, then it also seems possible that there is an abstract moral factor in having the ability to exnihilate, a factor absent (or present in a different/lesser way) in matter-rearranging. Aug 24, 2023 at 12:49
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    @KristianBerry btw the joke you are looking for regarding Aquinas' style is that he would probably say that "ought can be understood in two ways." He says that (or three or four ways) any time he perceives that disagreement or conflict is due to semantic confusion.
    – jaredad7
    Aug 24, 2023 at 12:56
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    This is getting long, but the main measure is to see which scenario realizes greatest enrichment of human life in line with the enriching evolution of existence that has already given us rich living organisms out of simple matter. Now I can cite empirical evidence showing why deviation from the heterosexual family and even its more traditional formations is in fact a devolutionary process leading to decay/trouble. For that I'll refer you to works by Marry Eberstadt.
    – infatuated
    Aug 24, 2023 at 18:17

Like Conifold said in comments, yes that's the only solution that is conceivable in principle. But the problem, again like he suggested, has always been a matter of identifying the telos not of logic.

Metaphysical telos are not a valid subject in modern Western philosophy as metaphysics is largely disapproved of due to failures of Christian Scholastic metaphysics. But the trouble is even telos that can be identified with good certainty by empirical science are also being denied. For example, sexual attributes are not apparently meant primarily for procreation in the eyes of proponents of homosexuality and gender affirmation that are getting growing reception in the modern West.

Part of reason, I'd aruge, is that modern physicalist paradigm has preempted possibility of a deeper psychology to address the psychological side of alleged "gender confusion disorders", hence normalization of homosexuality becomes inevitable with traditional opponents portrayed as bigots. Also a scientific community obsessed with physicalist/physiologistic approach to human psychology will inevitably authorize gross anatomic disfigurement of sexual reassignment surgery to treat a problem that a psychological solution to it, if had, may have treated without the radical anatomic alteration.

Now I want to propose an additional element for a teleological metaphysical solution to the ought-is problem. The problem is best resolved under a process metaphysics which highlights the dynamic and developmental nature of existence. Therefore outght-to statements can be seen as logical expression of an ontological tendency, of beings tending to evolve and achieve ends. Therefore human physiology only reflects the same universal directedness and developmental nature of existence. So the physiological division of mankind into two sexes and its reproductive function must be a consequence of a universal metaphysical process driving all beings towards survival and higher forms of existence as in collective family life.

On the psychological side, this means affirming the dynamic nature of human consciousness and existence of mental causation. So while the Cartesian cogito argument establishes the existence (isness) of human consciousness, acknowledging the active and causal nature of that existence (oughtness) helps explain how is and ought are just different sides of the reality of man and universe.

  • Do you have some examples of the failures of Christian Scholastic metaphysics according to modern Western philosophy? Actually, I am thinking this might warrant a separate question.
    – jaredad7
    Aug 24, 2023 at 12:37
  • @jaredad7 Yes, a broad topic. It's a failure in grounding metaphysics in mystical experience and self-evident truths of a robust rational psychology. Descartes attempted it which was too late and ultimately dismissed for inconsistency with his mechanistic cosmology ("ghost in the machine"). Other errors involved canonization of Aristotelianism which eventually discredited whole of Christian theology. All of on a backdrop of long-held belief in dichotomy between faith and reason, which was finally came to a head with Kant questioning any metaphysics. And there's more...
    – infatuated
    Aug 24, 2023 at 14:36

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