Removing the Blades from Hume’s Guillotine

by Tauriq Moosa

David-Hume-Scotland-17111776-289536 Hume’s Guillotine: “One cannot derive an “ought” from an “is”. This thesis, which comes from a famous passage in Hume's Treatise [says]: there is a class of statements of fact which is logically distinct from a class of statements of value. No set of statements of fact by themselves entails any statement of value. Put in more contemporary terminology, no set of descriptive statements can entail an evaluative statement without the addition of at least one evaluative premise. To believe otherwise is to commit what has been called the naturalistic fallacy.”

– John Searle, ‘How to Derive an “Ought” from an “Is”’, The Philosophical Review, 1964

Beware, people. This is a long piece. Even I’m uncertain about it. Here we go then.


Major ethicists like Immanuel Kant and indeed – to an extent – Thomas Aquinas sought to establish a rational basis for deriving moral considerations. Why rationality above other justifications? Consider: one and one is two. This is a statement that appears to hold true regardless of the state of the world, whether we’re dreaming or awake (as Descartes famously pointed out in his Meditations), whether we’re in pain, and so on. However there is an implicit assumption being made here, too: that if we do agree that one and one is two, we who agree to this statement are rational agents; that is, beings who accept the constraints and rules of logic and rationality.

This appears to only beg the question: Why should anyone accept that one and one is two? (This problem so vexed the young Bertrand Russell, that he nearly mentally destroyed himself as an adult trying to establish conclusively that one and one is two.) As Sam Harris has said, how do you convince a person not interested in rationality to use rationality? As soon as you start making rational arguments, you’ve already lost.

The method of argumentation we use is premised on some basic axiomatic assumptions of rationality; for example, if you are carrying an umbrella, are wet and I hear thunder, I can infer it is raining. Yet the conclusion “it is raining” makes sense only if we accept that it follows from those premises. Someone may say there is no reason to accept it is raining, despite being drenched. But then, like all persons refusing to accept rational axioms, he has removed himself from the conversation.

This has implications for moral thinking, though. It does not appear to be the same thing as saying abhorrence or disgust is completely not rational. The difference here is there are actually good descriptive reasons why people claim disgust equals immoral, but those are not normative reasons. This means we must separate the charge of rational moral deliberation when faced with emotional judgements: (1) If people use the emotions as the only and complete basis for a moral judgement, they must be challenged; but (2) if we are saying these people have absolutely no basis for saying, say, prostitution is repugnant therefore it is wrong, then we are making a different claim. There are descriptive reasons why people find selling bodies, sexual favour, etc., abhorrent. The mistake is the next step they make: saying all things that are repugnant are immoral. But I don’t want to focus on this.

Why should we rely on, say, reason – whatever that means – instead of non-rational-based justifications, like gut-reactions? Why shouldn’t our abhorrence at, say, homosexuality or rape constitute enough justification to claim something immoral? Who would dare say such things are not disgusting and therefore wrong?

Disgust, abhorrence, revulsion, repugnance. Whatever your chosen word or synonym is, these appear to many people the entire basis of judging something right or wrong. Yet, no administration or public policy would be justified to implement, say, a policy legalising ‘active’ euthanasia based on nothing but feeling.

Despite my own support of legalising assisted-suicide (all viable forms thereof), I would not support euthanasia groups that rest their justifications on sentiment, feeling, and so on; since these are no different to opposition groups that claim things like “killing an innocent is wrong because it is abhorrent, goes against god’s law, and so on”. Neither side, despite one arguing for something I would consider an good ethical action, is correct in its justifications by appealing to something unhelpful like feelings or emotions.

However, we cannot simply dismiss ideas that are non-rational as a whole. The great David Hume famously realised this in his Enquiry Concerning the Principles of Morals. This quotation is worth showing in full (if only to have an excuse to relish in the man’s writing).

It appears evident that the ultimate ends of human actions can never, in any case, be accounted for by reason, but recommend themselves entirely to the sentiments and affections of mankind, without any dependence on the intellectual faculties. Ask a man why he uses exercise; he will answer, because he desires to keep his health. If you then enquire, why he desires health, he will readily reply, because sickness is painful. If you push your enquiries farther, and desire a reason why he hates pain, it is impossible he can ever give any. This is an ultimate end, and is never referred to any other object.

Perhaps to your second question, why he desires health, he may also reply, that it is necessary for the exercise of his calling. If you ask, why he is anxious on that head, he will answer, because he desires to get money. If you demand Why? It is the instrument of pleasure, says he. And beyond this it is an absurdity to ask for a reason. It is impossible there can be a progress in infinitum; and that one thing can always be a reason why another is desired. Something must be desirable on its own account, and because of its immediate accord or agreement with human sentiment and affection. (from An Enquiry into the Principles of Morals, Appendix 1, V.)

James Rachels summarised this quotation in his brilliant book, The End of Life. Says Rachels: “Arguments can take us only so far; at some point in our reasoning we will always come to some assumption that we must take for granted without argument.”

If our fundamentals are not based on reason alone, if our justification for action is not premised on pure, sound rationality, are we resting important arguments on heart-strings, sentiment and mere human need?


Hume’s great project was looking at reason’s place in all thought; yet he seemed to always find that reason was either not as reasonable as it appeared or, when it was, meant nothing in terms of moving people toward action. Perhaps his most famous quotation indicates as much. In his Treatise of Human Nature, he says: “Reason is, and ought only to be the slave of the passions, and can never pretend to any other office than to serve and obey them.” It is not reason that causes us toward developing hunting tools of efficiency, but hunger, yearning and so on. Reason carves the blades to be more efficient; reason allows us to develop poisons, spices and traps. But reason is merely a slave to passion’s whip, as it flails for itself to be sated using reason as an auxiliary for its own satisfaction.

This means no matter our theorising, our moral thinking (amidst other forms of thinking) is a way to satisfy some non-rational part of ourselves. This is not as devastating as it first appears, since we can have two responses: (1) We can agree and continue our business or (2) find a way to answer it using examples of pure rationality like one and one is two.

To agree is to submit to a description. Of course humans are moved and driven by passion; yet argument can change minds. There doesn’t appear to be a way to measure which is more potent but it appears that sentiments, emotion and so on, are more effective than rational engagement. Renowned researcher into emotions, neuroscientist Antonia Damasio, says studies he investigated found that “children who suffer brain injury in certain regions of the frontal lobe in their first year years of life develop major defects of social behavior in spite of being otherwise intelligent. They do not exhibit social emotions (compassion, shame, guilt) and they never learn social conventions and ethical rules.”

It certainly is evident to me that emotions move people more than rational argument from these pages, where I have made arguments that upset a few people. Yet to submit to this description barely lends itself toward moral engagement.

Hume also famously said he had never seen someone derive an ought from an is; that is, move from how the world is to how the world ought to be (this is Hume’s Guillotine).

Let us say it really is the case – though I don’t think it is – that reason holds no water in getting people to act; that it is only sentiment and passion that burns fuel in people’s hearts. Does that mean we throw up our hands when it comes to thinking how we ought to live, act, behave, engage, give, think? Does that mean we ignore ethical engagement and argument?

Of course not. It might simply mean we retain a sense of humility that even we who are attempting to engage with rational argument in ethics do so for non-rational reasons. We do so because we want to live in a better world; we do so because we have reasoned about our non-rational engagements. We have asked ourselves is it good that I want x, y, and z?

After all, I may want to smoke a cigarette, to achieve that nicotine rush; I may want that extra, juicy piece of steak. But reasoning about it has shown me that I will kill myself faster and am harming other beings (for both smoking and eating meat). Here we can use rationality to weigh up the passion being fulfilled: What matters more: satisfying my habit and taste or being healthier and not causing suffering? Each of those things is something I want. Each of those is something many people want. Yet how do we weigh them, except to say I want a reduction of suffering and health more than I want the other desires. Is there a rational reason that doesn’t amount to merely satisfying a non-rational sentiment like health and a feeling of empathy? Does it make sense to say I want to desire?

If I say this – or admit this – can I reasonably convince others of the same conclusion? Certainly I can offer them evidence that harm is occurring, that health is being negatively affected. If they are more concerned with living healthier, then it is reasonable to not smoke, given the available evidence. The information is there and freely available. Yet: We still have smokers and meat-eaters; either they do not want to live longer, do not care, are addicted, want the rush more than extended life, etc. Whatever it is, this does not mean we give up trying to convince since my small thought-process demonstrated in the previous paragraphs shows both reason and passion in play.


But I’m not satisfied with such explanations. They appear too easy and a cop-out. I want to try another method, which I’m not sure is as successful as submitting to humility. I want to say that we must come to a definition of moral thinking: whether it is about maximising well-being, reducing suffering, and so on. Once we achieve a definition, I don’t see how we can better engage with it save through rationality; more specifically using a scientific methodology.

What I’m trying to get at is to remove the idea that moral action is primarily about satisfying a non-rational urge. This I concede is perhaps something that drives any of our actions. It’s hard to envisage an action that we perform that is not about benefitting us individually (this is what makes psychological egoism so frustrating and disgustingly satisfying). If we admit that all action is about satisfying some sentiment or desire, Hume’s notion is entirely uninteresting since it affects everything we do, not just moral deliberation. This means everything from turning on a light-switch to debating euthanasia policy is premised on the same thing: satisfying some personal desire or sentiment.

If this is so, we can dismiss it as relevant to a fruitful moral discussion, just as we don’t worry whether solving mathematical problems is really just about sating some personal sentiment or passion. It’s not relevant.

Secondly, after coming to a definition we can say whether we’re satisfying the definition or not. For example, let us assume for the purposes of this piece that ethical actions are ones that reduce suffering for relevant agents. We can then go about deciding whether we are or are not reducing suffering; who count as relevant agents (rocks, cabbages, rabbits or Bin Laden) ; and so on. Therefore our definition of morality is explained. To ask “Why should I be moral?” would be the same as asking “Why should I accept one and one is two?” The person has removed himself from the question. Ethical action just is that which reduces suffering; as one and one just is two; as a bachelor just is an unmarried man.

However, if you do ask “Why should I reduce suffering?”, we may attempt various arguments: It is beneficial to oneself, it’s a duty, etc., but I think this misses the point of what I’m trying to achieve. With this out the way, we can go about using scientific models to actually decide whether we’re being ethical or not.


I’m uncertain whether this is a sound argument. I have a suspicion it is not precisely because I’m fond of the outcome were it to be the case. Therefore, I’m probably enthusiastic because I’m operating under the confirmation bias. The reason I like this idea, and the reason I might be severely mistaken, is it overcomes the unnecessary abstract ethical circles and actually engages with making a difference: that is, fulfilling ethical obligations (reducing suffering, improving lives, or whatever it is that becomes the definition of morality).

We can say “Ethical action is about doing x”. If it is – which it has to be by definition – then we can engage in measurement, self-criticism, evidence, argument. This, after all, is how we successfully convince governments to, say, legalise euthanasia – operating on shared assumptions of action, about what matters, showing that the previous way of doing it was wrong, then changing it. However, another important reason I like this methodology is that it allows for a better basis for critics. To continue using euthanasia as the focus, critics might say “It will be abused”. We can say “Let us look at the evidence.” This means we can try solving these very important discussions on a platform that isn’t about whether we’re conservative or liberal or utilitarians, etc., but about whether the statistics indicate a violation of the original proscription. If the violation is happening – like too many people being killed against their will – then we are in fact not acting morally according to the very definition we assumed. Therefore we can retract the legalised stance and the previous moral decision.

This is how it overcomes Hume’s Guillotine – or deriving an ought from an is – because we basically eliminate ‘ought’. If ethics is reducing suffering (which we’re assuming for this column), then it isn’t whether we should reduce suffering but whether a certain action does. If it does, then we do it. There is no ought. To end this suddenly, I realise a number of things.

Firstly, the literature in philosophy is vast on this subject. Many brilliant minds have spoken in defence of saying you can derive an ought from an is. I, who know little about philosophy in general and ethics in particular, cannot hope to make a dent for many on this topic (I don’t do ‘hope’, but that’s for another time!). The reason this seems satisfying is well explained by Alasdair MacIntyre in his After Virtue, and first said famously by GEM Anscombe. And these are two theorists I disagree with on most things.

Secondly, some might claim I’m making either ‘the naturalistic fallacy’ or operating upon tautologies. The poorly-named naturalistic fallacy entails calling something, say, good based upon its inherent property. GE Moore introduced the fallacy but he has been seriously criticised, enough to warrant scepticism about whether the fallacy is even a fallacy by definition. Arthur Prior outlines the fallacy as such: “If, for example, it is believed that whatever is pleasant is and must be good, or that whatever is good is and must be pleasant, or both, it is committing the naturalistic fallacy to infer from this that goodness and pleasantness are one and the same quality.” So to apply to me that would be saying “reducing suffering is good” or “it is good to reduce suffering”.

A rule-of-thumb to detect the naturalistic fallacy is to see whether we can ask whether the thing described as good really is good. Thus: Is it good that we reduce suffering? If we answer yes, then we have still more work to say why. However, for me this amounts to asking “Is good good”? This is as nonsensical a question as challenging the statement “a bachelor is an unmarried man”; yet in the latter we find nothing tautological or wrong here. I want say that the definition for morality just is reducing suffering (or whatever). If we are the same rational beings that accepts mathematical answers, then we are the same beings that accept ethics as reducing suffering. It is nonsensical to me to apply the Guillotine, the naturalistic fallacy or the tautology because then you are simply mistaken about definitions (yet another area I know little about. Thanks, Kripke).

For an outline on the opposing side, i.e., those not convinced by this kind of thinking, see the clearly written post by fellow 3QD columnist Julia Galef at (one of my favourite blogs) Rationally Speaking. Here all her arguments seem strange to me because I see it as missing the point, because I see us as having decided on ethical action then moving to see what the most efficient way to implement it is. (I suppose, what she and others will challenge is “What is ethical?” I see no reason why this is a challenge though. If an ethical action doesn’t, say, have the property of reducing suffering for relevant beings, it –by definition – removes itself from counting as moral!)

A third and possibly more devastating idea comes from the idea of abhorrence. For example, I can assert that ethics is about reducing suffering, but someone else can assert that abhorrence is more important. That is, if something is abhorrent it just is immoral. We can just say: “that’s the definition of immorality”. This seems to me the most devastating idea for my point. I have not yet formulated a response. Perhaps we can say that these people are simply mistaken or that if ethics is about reducing suffering, then we have good reasons for dismissing non-scientific methodological methods of justifying ethical action. This however seems unsatisfying and my opponent retains this argument. After all, we might ask, why should he accept my definition? I might simply say “Why should anyone accept the definition of bachelor is an unmarried man?” My opponent can say: “Why should anyone not accept that abhorrence just is immorality?” The only reply I can think of, for now, is that we have already defined morality and abhorrence does not fit within our definition. It’s like trying to say a chair isn’t a bachelor, therefore, anything that isn’t a bachelor is a chair.

But again, these don’t seem like satisfactory replies to my critic.

The important thing for me is remaining in the place where our actions make a difference. To allow ourselves to become bogged down by wondering “where morality comes from”, “why should I be moral?”, and so on, seems useless. What is the best way to improve the world, aid others, decrease suffering? I’m interested because of the horrible world we live in, which continually exists with all the mistakes, errors, and mistaken judgements made by others before us and currently.

I would certainly like for this to be the basis of moral engagement, where we can begin using methods we can all agree upon – for example, does legalising euthanasia reduce suffering or lead to exploitation and murder; does the death-penalty reduce crime and so on. Again, this is what I would like to be the case and I’ve argued because of this. This is what troubles me, since this is a bad reason to assert what could ultimately be seen as absolute idiocy. I’m uncertain about this move and about this whole argument, but I’ve argued for it here. Hindsight, criticism and engagement will show me.