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Hume, His Guillotine, and the Being of Ought

January 20, AD2017 2 Comments

You probably had your first experience of reality long before you were born, in your mother’s womb. From that experience, a small handful of crucial ideations were created. It was your first experience of otherness, as well as your first experience of selfness because I came in contact with something that was not I. This is something other than me; I am something other than this. It was not you; it was something outside of you; something that was and was, therefore, real. Before you came into the world, you had ideas that only needed appropriate words to convey them.

The Birth of Ought

In learning your language, you learned what distinguished one Other from another, as well as what distinguished them from yourself. You learned distinctions in family relationships, spatial relationships, temporal relationships, colors, numbers, sounds, smells, tastes, shapes, occupations, and actions. You also learned to make distinctions within yourself, not only distinguishing hands from feet and eyes from ears but also want from satisfaction, anger from contentment, sorrow from happiness, fear from trust. The original associations you were born with — self, other, is, is not — were subdivided into further associations and connected with everything you learned how to label.

Gradually, you made sense of the world.

Along the way, there was another distinction you learned to make — is and ought. It possibly happened the first time you were hungry: something about you is that should not be. Suddenly, the real gave birth to the ideal, born from your first sensation of the not- of function, dysfunction. You suffered privation of a good; you wanted because you lacked. Something had gone wrong. It was also your first experience of the imperfection of life, but not your last. And also born with it was the imperative to correct the dysfunction, prompting you to notify your parents with a sleep-shattering wail.

David Hume Builds a Guillotine

The so-called is-ought problem stems from a passage in David Hume’s A Treatise of Human Nature. In the passage, Hume claims that ethical philosophers begin with is/is not statements, then suddenly introduce ought/ought not statements. However, Hume argued, ought can’t be observed and explained from The Way Things Are. “For as this ought, or ought not, expresses some new relation or affirmation, ’tis necessary that it should be observed and explained; and at the same time that a reason should be given, for what seems altogether inconceivable, how this new relation can be a deduction from others, which are entirely different from it” (op. cit., p. 245). How, Hume asks rhetorically, can we derive from the way the universe does work the way it ought to work?

This argument has come to be known as Hume’s Guillotine. Hume, in this fashion, is the great-grandfather of scientism, that late-blooming shoot of logical positivism which holds that only Science can produce Truth. But Hume is trying to put the scientific cart in front of the philosophical horse. Scientism goes further: it tries to do away with the horse altogether, in the mistaken belief that the cart is motorized.

Speaking of motors: I get into my car, insert the key, and turn the ignition to “on”. By Hume’s rule, if my engine fails to turn over, let alone start, I ought not(!) deduce that anything has gone wrong — whatever happens is whatever’s supposed to happen, and I have no rational grounds to expect anything different. Switching to the ethical mode: If I lie to you, and you get hurt from acting on my falsehood, you can’t abstract from it the moral imperative People ought to tell the truth because you can’t know The Way Things are Supposed to Be from observing The Way Things Are.

There Is an Ought

You might have seen the problem already and begun laughing. This is one of those things you wonder if people really believe even when they’re saying it. For Hume can’t even finish the statement quoted without introducing a prescriptive — “… [ought] should be observed and explained; and … a reason should be given ….” Nor is this the only example of Hume introducing a normative principle:

“I began this subject with premising that we ought to have an implicit faith in our senses, and that this would be the conclusion, I should draw from the whole of my reasoning” (ibid., p. 116; spelling modernized).

“Since therefore ’tis almost impossible for the mind of man to rest, like those of beasts, in that narrow circle of objects, which are the subject of daily conversation and action, we ought only to deliberate concerning the choice of our guide, and ought to prefer that which is safest and most agreeable” (ibid., p. 143).

If all we can know is how people do behave, then we can’t derive from it an idea of how people should behave. And one of the ways they do behave is that they import normative statements from outside the set of observables. Why should they behave any differently? Why ought we have an implicit faith in our senses, or prefer the safest and most agreeable guide to anything, if we don’t do so already? Why should we do anything we aren’t doing, or stop doing things we are doing? If you can’t get the ethical from the actual, then you can’t derive from What Really Happens a moral duty to avoid importing moral duties. The position is self-referentially incoherent: Hume’s Guillotine cuts off the inventor’s own head.

This isn’t to say that our natural experience of is leads to consistent ideas of ought. Having been lied to, I can abstract the principle No one ought to lie; but I can just as easily abstract the principle I ought to lie as well, and not trust anyone to tell me the truth. Which one you pick depends on your overarching principles, and whether you’re thinking of the community or just yourself. The point, however, is that we can know what ought to be from what is. Just as there is an is, there is an ought.

Fact-Value Distinctions and Science

The fact-value distinction, according to theologian John C. Médaille, is rooted in medieval theology:

The medieval theologians insisted that the material world reflected the eternal order of God and operated on God-given laws which could be known without direct reference to theology. This allowed a measure of autonomy for the physical sciences. The distinction was not a real distinction, however, but a methodological one confined to physical motions; the motions of the human will could not so easily be measured and numbered. With the Enlightenment sages, however, the distinction became a real one — an ontological distinction — that extended even to human motions. All motions, even human ones, would be reduced to number and quantity and divorced from theology and ethics. (Toward a Truly Free Market, pp. 27-28)

The problem, as Hume’s is-ought prescription so tellingly demonstrates, is that you can’t even start doing science without making value judgments. The sciences all assume a telos, a final cause or purpose for the discipline, thus setting that purpose as the discipline’s supreme “good”. There are other value judgments that define how the discipline is pursued; the disciplines historically choose truth ever falsehood, objectivity over subjectivity, reason over intuition or emotion, method over improvisation, empiricism over rationalism, and so forth. Values tell you not only what methods are permissible and not permissible, but why there should be methodological rules.

Assumptions and Proof

Values, and the moral scheme which produces them are logically and necessarily prior to science, and how science proceeds is contingent on them. A “value-free science” couldn’t even begin to define itself, let alone justify itself. That’s why scientists could never use science to empirically determine a moral scheme: they don’t, and can’t, start from a value-free position, and could only “find” the values they brought into the lab with them.

Fact-value distinctions can be difficult. Médaille points out that, for an economist, opportunity costs are facts because they can be assigned numbers, while marital fidelity is a “mere” value; on the other hand, adultery has an ontological presence to which history and observation attest, while “opportunity cost” is a theoretical abstraction not easily found in the historical record (Médaille, p. 30). Because we inhabit a moral universe and must have values to survive as a community, we treat moral values as facts even when we insist that moral values are relative and have no empirical grounding. Hume’s Guillotine is the result of poor fact-value distinctions; the values he attempted to import into science were facts to him.

Hume was an empiricist. There’s no sin in that; St. Thomas Aquinas himself argued that we first know things through the senses. Hume’s error lies in wanting everything reduced to numbers or physical evidence before it can be declared known. Hume wanted science to be a golden hammer and didn’t want to be bothered with anything that couldn’t be treated like a nail. But science begins by assuming things, such as the validity of reason (you can neither prove nor disprove that validity without tacitly assuming it works to some degree). If nothing can be assumed, nothing can be proven. Science can’t prove that only numbers and physical evidence are knowable precisely because science itself is limited to mathematical and empirical tools; to even attempt to prove it would be like searching for synchronicity using a metal detector.


I’ve done David Hume the courtesy of assuming honest if erring intent. That is, he did not wish to dispose of morality per se but only put it on what he felt was a more firm footing. However, with his air of supercilious authority, Hume managed to convince almost three centuries’ worth of philosophers to ignore what their own experience and observations told them, that we know things we can’t reduce to numbers or test in a lab. Hume’s Guillotine is a fraud, a demonstration of the principle that people believe an error spoken with confidence sooner than a fact spoken with hesitation.

What’s a source of epistemic uncertainty to the logical positivist is merely common sense to the Thomist Christian. We know from our earliest days that reality can fail to meet reasonable expectations, that things can go wrong and need to be set right again. We don’t only know this from our own experience; we observe people abstracting ought from is and importing moral values all the time. It’s not only what we do; it’s what we have to do to survive and thrive. We not only know what ought to be; we can know it in a way that neither needs nor admits of empirical proof.

Commit Hume’s Guillotine then to the flames: for it contains nothing but sophistry and illusion.

Photography: See our Photographers page.

About the Author:

Born in Albuquerque, N. Mex., and raised in Omaha, Nebr., Anthony S. Layne served briefly in the U.S. Marine Corps and attended the University of Nebraska at Omaha as a sociology major while holding a variety of jobs. Tony was a "C-and-E Catholic" until, while defending the Faith during the scandals of 2002, he discovered the beauty of Catholic orthodoxy. He currently lives in Denton, Texas, works as an insurance agent and in-home caregiver, participates in his parish's Knights of Columbus council and as a Minister to the Sick, and bowls poorly on Sunday nights. Along with Catholic Stand, he also contributes to New Evangelization Monthly and occasionally writes for his own blogs, Outside the Asylum and The Impractical Catholic.

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