Are Ethics as Necessary as Math?
Exploring whether moral principles are invariant
You don’t need a placebo-controlled study to know that 2+2=4. No amount of evidence could make it false, and no absence of evidence could make it uncertain — it isn’t the kind of claim that observation could ever bear on. That’s what makes mathematical truths different from empirical ones. A crash-data statistic is true or false because of what happened on the road; it’s revisable, in principle, by better data. “2+2=4” isn’t revisable by anything at all.
The question I can’t stop turning over is whether any moral principle belongs in that second category. Is the statement “wanton cruelty is wrong” more like a crash-data statistic — well or poorly supported by evidence, contingent on how things happen to have gone — or is it more like arithmetic: true regardless of anyone’s beliefs, anyone’s culture, anyone’s survival?
Two alternative answers suggest themselves immediately, and I don’t think either survives close inspection.
The first alternative is that morality is simply what evolution built into us — cruelty and empathy as rival strategies, with whichever one wins the reproductive contest “proving” itself right. It’s a tempting picture, and it isn’t hard to find evolutionary just-so stories that make it feel almost self-evident. But it doesn’t hold up. Evolution can tell you why a trait spread; it can’t tell you the trait was moral, without smuggling in an extra premise nobody’s defended. And the premise has teeth: if “whatever wins reproductively is right,” then the conquests of the Mongol imperial clan were right, for exactly as long as they kept winning, since they spread a Y-chromosome lineage now carried by an estimated 8% of men across a huge swath of Asia. So was the demographic replacement of Neolithic Europe by Bronze Age populations, documented in the ancient DNA record. Most people, pressed on it, don’t actually want to say that de-facto genocide is right — which means “successful at propagating” can’t be what “right” means.
The second alternative is that moral principles simply are, the way mathematical facts are — invariant, mind-independent, waiting to be discovered rather than invented. This is a more serious position, but it inherits mathematical Platonism’s oldest problem: if numbers are purely abstract, existing outside space and time, how does a concrete, physical mind ever come to know anything true about them? Moral principles, if purely abstract, face the same puzzle. And there is a further worry: a mind shaped by selection pressure has no obvious reason to have latched onto “true” morals, rather than merely useful ones, if the two ever came apart. Why trust the intuition at all?
Between those two failures sits a third option, one that neither asks morality to be discovered nor reduces it to “whatever wins.” Christine Korsgaard‘s “constructivist“ version of Immanuel Kant‘s “categorical imperative“ argument holds that moral truths, rather than existing independently, arise from the very practice of acting for reasons. This sidesteps both earlier problems at once: no derivation of “ought” from an evolutionary “is,” and no purely abstract realm to have mysterious contact with.
It comes at a real cost, though, and the cost is worth stating plainly rather than glossing over. “2+2=4” is true even in a universe with no minds in it at all; constructivist moral truths would not be. They’re necessary given rational agency — closer to “a bishop moves diagonally, if you’re playing chess” than to “2+2=4.” That’s a genuine downgrade from the kind of invariance I started out chasing, even if it’s still a serious, defensible position.
And there’s a sharper objection waiting underneath it. David Enoch calls it the “shmagency” problem. Korsgaard’s argument says that if you don’t live up to the standards constitutive of full rational agency, you fail at being an agent. Enoch’s reply: so what? Suppose I don’t care about qualifying as a capital-A “Agent” in the technical sense — suppose I’m content to be a “shmagent,” something that acts, pursues goals, gets things done, but is indifferent to whether it clears Korsgaard’s stricter bar. Why is that a practical failure, giving me any reason to comply, rather than a merely definitional one — the way failing to count as a “bachelor” because I’m married isn’t a failure of anything? Korsgaard’s own answer is that you can’t actually opt out this way, because even the act of declining is itself an act, performed for reasons, which already puts you inside the very game you’re trying to refuse. Whether that reply actually closes the gap, or just relocates it, is a live and unresolved argument in the literature — not something I’m going to settle here.
Here’s a case that puts real pressure on all three views at once, rather than letting any of them stay comfortably abstract.
Someone presents you with a gasoline-drenched puppy and a lighter, and tells you: burn it alive, or I’ll kill you. (Set aside the old Cartesian view, once seriously held, that animals are mere automata incapable of suffering at all — grant that the puppy can suffer, and the dilemma still stands.)
If you flick the lighter in this scenario, it isn’t an act of wanton cruelty on your part; your act is coerced, and aimed at a purpose — your own survival — that exists independently of the suffering. That distinction matters, because most legal and moral traditions already track it: duress can reduce an agent’s blame without making the underlying act not wrong. A very clear real-life case is R v. Dudley and Stephens (1884): shipwrecked sailors, starving, killed and ate the weakest of their crew to survive. English law held that necessity is no defense to murder — the killing remained wrong. But the court’s own sentence was ultimately commuted from death to six months’ imprisonment, in recognition of just how extreme the circumstances were.
The three views don’t agree on why, or even on whether, burning the puppy is wrong.
An evolutionary account has almost nothing to say here beyond noting that prioritizing your own survival over another species’ member is exactly what selection would predict. It doesn’t obviously give the puppy’s suffering any weight independent of your own survival calculus.
A moral realist has to decide whether self-preservation under lethal threat is an adequate justification — making the act permissible — or merely an excuse — leaving the act wrong while reducing blame. Serious people land on both sides of that line, and nothing about realism itself settles it. That’s not a small gap: realism, as I’ve described it here, is a claim about the status of moral facts — that they’re out there, mind-independent — not a method for finding them. It gives you nowhere to stand when weighing your own survival against someone else’s suffering; it just insists some fact of the matter exists, without supplying any way to reach it.
Constructivism does better here, and not by accident. Korsgaard’s own extension of the framework, in Fellow Creatures (2018), holds that any sentient creature must be treated as an end, never merely as a means. That’s close to an absolute constraint — it’s the same reasoning behind Kant’s notoriously strict position that you shouldn’t even lie to a murderer at your door. Using the puppy’s suffering purely as a means to your own survival is exactly the kind of instrumentalization that formula rules out. That doesn’t make the act any less understandable under threat, but it gives constructivism real grounds — where realism had none — to say the act can be excused without ever being fully justified, mirroring the Dudley and Stephens precedent precisely rather than just gesturing at it. Realism is silent on method and genuinely undecided; constructivism has an actual procedure built into its foundations, and that procedure leans toward a stricter, more decisive answer.
So where does that leave the invariance I went looking for? Evolutionary reduction can’t get from “won” to “right.” Realism owes an answer, which it may not have, to how an evolved mind could ever reliably track a truth that has no causal effect on anything — including on the mind trying to track it. And constructivism — the most promising of the three — turns out to buy its escape from those problems by quietly trading away the very thing I started out looking for: a truth that would hold in an empty universe. Constructivism’s truths hold only for creatures capable of acting for reasons — and, per the “shmagency” problem, hasn’t fully closed the door on simply declining to care whether you qualify.
Even with that question still open, constructivism offers firmer ground than either alternative; it’s just not the moral invariance I set out to find.
I first raised this question in “The Mirror Thinks Back,” a trilogy on AI consciousness, with a promise to give it an essay of its own eventually. This is that essay.