I was reading a debate about animal rights the other day when I noticed something strange. The argument went like this: factory farming causes tremendous suffering to animals. Animals are sentient beings capable of pain. Therefore, we shouldn’t eat factory-farmed meat.
It sounds reasonable enough. But there’s a peculiar little jump happening in that final step — one that a grumpy Scottish philosopher named David Hume spotted nearly 300 years ago. We go from observing facts about the world (animals suffer, they’re sentient) to making a moral claim (we shouldn’t cause that suffering). We leap from “is” to “ought.” And according to Hume, that leap might be impossible.
The Great Divide
Hume’s insight — sometimes called the is-ought problem or Hume’s guillotine because it seems to cut cleanly between two types of statements — is deceptively simple. You can pile up descriptive facts about the world until you’re blue in the face, but you’ll never logically derive a prescription for what you should do about those facts.
Consider: “John promised to meet Sarah at 3 PM. It’s now 3 PM. John is not there. Therefore, John broke his promise.” So far, so good — all descriptive statements that follow logically from each other.
But what if we add: “Therefore, John did something wrong”?
Suddenly we’ve introduced a moral evaluation that wasn’t lurking in the premises. We’ve smuggled in the assumption that promise-breaking is wrong. But that assumption — that ought — came from somewhere else entirely.
This bothers me more than it probably should. I like arguments to work cleanly. I want to be able to point to facts about the world and say, “Look, there’s the answer to our moral questions.” But Hume suggests that’s not how it goes.
The Missing Bridge
The problem isn’t that moral arguments are impossible. It’s that they all seem to require at least one premise that isn’t purely factual — some bridge principle that connects the is-world to the ought-world.
Take utilitarianism, the view that we should maximize happiness and minimize suffering. John Stuart Mill — who came after Hume — tried to ground this in the fact that people actually desire happiness. We can observe that empirically, can’t we? People seek pleasure and avoid pain. Shouldn’t that tell us something about what’s good?
But notice the hidden step: from “people desire X” to “X is desirable” to “we ought to promote X.” Each transition requires an assumption that isn’t itself a mere observation. Why should the fact that people want something make it good? Why should what’s good for individuals scale up to moral obligations for everyone?
I’m not trying to demolish utilitarianism here. I find it pretty compelling, actually. But Hume’s point stands: even the most fact-based moral theory needs at least one non-factual premise to get off the ground.
Does This Matter?
Here’s where I sometimes wonder if Hume discovered a genuine philosophical problem or just pointed out something obvious that we’d been ignoring. Of course moral claims aren’t identical to factual claims. If they were, we wouldn’t need different words for them.
But it matters because so many of our moral and political arguments proceed as if we can read our values directly off the natural world. “It’s natural, therefore it’s good.” “It’s the way things have always been done.” “Science shows that cooperation benefits survival, therefore we should cooperate.”
All of these arguments commit some version of Hume’s fallacy. They treat the descriptive and normative as if they lived in the same logical neighborhood, when they might be on entirely different continents.
This doesn’t mean science and observation are irrelevant to ethics. Far from it. If you want to reduce suffering, you need to know what actually causes suffering and what actually alleviates it. Facts constrain moral reasoning, even if they don’t determine it.
But it does mean that purely empirical approaches to morality are probably doomed. You can’t escape the need for some non-empirical starting point — some basic value judgment that isn’t itself derived from observation.
Living with the Gap
I’ve come to think of Hume’s guillotine less as a devastating critique of moral reasoning and more as a reminder of what moral reasoning actually involves. We’re not discovering moral truths the way we discover planets or chemical elements. We’re constructing them, starting from basic intuitions or commitments that we can’t fully justify through pure reason.
That might sound relativistic, but it doesn’t have to be. Maybe our basic moral intuitions — that suffering is bad, that fairness matters, that people deserve consideration — are arbitrary in some ultimate sense. But they’re not arbitrary to us. They’re what we care about, deeply and consistently, when we’re thinking clearly.
The gap between is and ought might be unbridgeable. But perhaps we don’t need a bridge. Perhaps we just need to be honest about which side we’re standing on, and why we chose to stand there.
When I think about that animal rights argument now, I don’t see it as fatally flawed. I see it as incomplete. The facts about animal suffering matter enormously. But they matter because I — we — have already decided that unnecessary suffering is something worth preventing. That’s not a conclusion I derived from the facts. It’s a value I brought to them.
And maybe that’s enough.