The framing to fix first: secular ethics almost never refutes Hume’s logical claim. The narrow point — that no valid deduction runs from premises containing only “is” to a conclusion containing “ought” — is granted by nearly everyone. What is disputed is what follows from it. So the honest question is not “how do you defeat Hume” but “which of the secular strategies for handling the gap holds up.” There are roughly five families, and only one of them tries to deduce an ought from an is.
What actually needs answering
Three distinctions do most of the clarifying work before any strategy is assessed.
- The narrow logical claim versus the substantive worry. Hume (Treatise, Book III, Part I, Section I) makes a point about deductive validity: the conclusion cannot contain a term absent from the premises. Grant it. The substantive worry — can facts about the world ground morality at all — is separate, and that is where the action is.
- Is/ought is not the naturalistic fallacy. These are constantly conflated. Hume’s gap is inferential. G.E. Moore’s naturalistic fallacy and open-question argument are semantic: the claim that “good” cannot be defined as any natural property, because “X is pleasant, but is it good?” always stays an open question. A secular naturalist has to answer both, and they take different answers.
- The gap can be technically leaky. A.N. Prior noted formal oddities (you can derive “ought”-containing disjunctions from pure “is” premises), which shows the “no ought from is” thesis needs careful statement about relevance and non-vacuous occurrence. This does not solve anything substantive, but it means the slogan is not as clean as debaters treat it.
Strategy 1: Deny the clean fact/value split
Thick concepts
Hilary Putnam (The Collapse of the Fact/Value Dichotomy, 2002) and Bernard Williams (Ethics and the Limits of Philosophy, 1985) argue the sharp partition Hume presupposes does not map onto real moral language. “Thick” ethical concepts such as cruel, courageous, generous, and treacherous are simultaneously world-guided and action-guiding: applying them correctly is a factual matter, yet the application already carries evaluation. If descriptive and evaluative content cannot be peeled apart, there is no seam for the gap to open along.
Putnam pushes further: even the sciences rely on epistemic values (coherence, simplicity, plausibility), so a pristine “value-free fact” is itself a fiction. Objection: critics grant thick concepts can be disentangled into a descriptive core plus a separable evaluative endorsement (Simon Blackburn, Allan Gibbard), which would restore the gap. Whether disentangling always succeeds is the live dispute.
Strategy 2: Close the gap for constitutive facts
John Searle, “How to Derive ‘Ought’ from ‘Is’” (1964), runs the promising case: from the brute fact that someone uttered the words of a promise, through the constitutive rules of the institution of promising, you reach “he ought to pay.” The engine is institutional facts — facts that exist only inside rule-governed practices (money, marriage, promising), where the descriptive fact and the obligation are internally linked.
Objection (R.M. Hare, and others): the derivation smuggles in a normative premise, namely that one ought to keep promises, or that by promising one has placed oneself under the institution’s rules. So the gap is closed only for those who already accept the institution. Still, it establishes that within constitutive practices the partition is genuinely porous, which is more than the textbook version allows.
Strategy 3: Reduce ought to natural fact
Two secular naturalisms claim moral facts just are natural facts, so there is no gap to cross, only a semantic illusion to dispel.
Cornell realism (Richard Boyd, David Brink, Peter Railton). Moral properties are natural properties, or supervene on and are constituted by them, even though not analytically definable. The identity is synthetic and a posteriori, like “water is H2O.” This directly answers Moore: that “is this good?” stays an open question no more shows good is non-natural than an ancient’s finding “is water H2O?” open showed water is not H2O. Railton’s “Moral Realism” (1986) reduces a person’s good to what they would want themselves to want under full information. Objection: the reduction bases (what people would want, what promotes flourishing) look like they are selected by a prior evaluative standard, so the normativity may be presupposed rather than reduced.
Natural goodness (the branch closest to your project)
Philippa Foot (Natural Goodness, 2001), Rosalind Hursthouse (On Virtue Ethics, 1999), and Michael Thompson (on the logic of the life-form) argue that evaluations of living things are plain factual evaluations: “a good oak,” “a defective wolf,” “the wolf that cannot hunt is failing as a wolf.” These are grounded in the species or life-form, not in sentiment. Human beings are living things, so ethical evaluation is a species of the natural-goodness evaluation that applies to every organism. The “ought” is a fact about what a flourishing member of the kind requires. This is the respectable secular cousin of the Randian move, without the survivalist thinness, and it lines up with the Rasmussen and Den Uyl flourishing route already in your notes. Main objection: the human “life-form” is far more plural and open-ended than a wolf’s, so which capacities count as constitutive of human flourishing reintroduces an evaluative choice.
Strategy 4: Relocate normativity into agency
Constructivism denies that oughts are read off external facts at all. Christine Korsgaard (The Sources of Normativity, 1996) argues normativity is generated by the reflective structure of rational agency: to act at all is to commit to valuing your own rational nature, and the ought follows from that self-constitution rather than from any fact about the world. You do not cross the gap; you show that any agent, simply by being an agent, is already under normative commitments.
This is the transcendental or retortion style — the ought as a condition of agency — and it structurally parallels the Objectivist “you are already valuing by arguing” move, but on Kantian rather than survivalist ground. Objection (the “shmagency” problem, David Enoch): why must one be an agent at all? If agency is optional, its internal norms bind only those who opt in, and the categorical force is lost.
Strategy 5: Grant the gap, deny the damage
The most Humean option: accept that no ought is deducible from bare facts, and argue this was never a defect, because morality was never grounded in deduction.
- Sentimentalism. Hume’s own view: reason is “the slave of the passions.” Oughts get their grip from moral sentiment plus facts, not from facts alone. Modern heirs run through Blackburn and Gibbard.
- Expressivism and quasi-realism (Simon Blackburn, Allan Gibbard). Moral judgments do not describe facts needing derivation; they express attitudes or plans. So “no ought from is” is trivially true — you cannot wring an attitude out of a belief by logic — but harmless, and quasi-realism then earns back the right to talk as though there are moral truths.
- Instrumentalism. Given an end already held, facts about means generate genuine oughts (“you ought to do what secures your end”). Fully factual once the end is fixed; the gap only reappears for categorical oughts. Objection to the whole family: it concedes there is no rationally mandatory morality binding the indifferent, which is exactly the categorical force many want ethics to have.
How the strategies trade off
They are not all competing for the same prize. Strategies 1 and 5 largely dissolve the problem (there is no clean gap, or the gap is real but toothless). Strategies 2 and 3 close it for a class of cases (constitutive facts, or a synthetic natural identity). Strategy 4 bypasses it (normativity comes from agency, not the world). The strongest single answer to a debate opponent wielding Hume as a cudgel is the combination the Objectivist underuses: point out that (a) the opponent almost certainly grants the narrow logical claim too, so it cannot by itself favor any view, and (b) their own foundation faces the identical structure. The strongest answer for building your own position is natural goodness or the flourishing reconstruction, because it grounds the ought in facts about the kind of being a human is without either sentiment-relativism or a smuggled categorical premise.
Sources
- David Hume, A Treatise of Human Nature (1739), Book III, Part I, Section I. Public domain: https://www.gutenberg.org/ebooks/4705
- G.E. Moore, Principia Ethica (1903) — the naturalistic fallacy and open-question argument. Public domain: https://www.gutenberg.org/ebooks/53430
- Hilary Putnam, The Collapse of the Fact/Value Dichotomy and Other Essays (Harvard, 2002).
- Bernard Williams, Ethics and the Limits of Philosophy (Harvard, 1985) — thick concepts.
- John Searle, “How to Derive ‘Ought’ from ‘Is’,” The Philosophical Review 73:1 (1964): 43–58.
- Peter Railton, “Moral Realism,” The Philosophical Review 95:2 (1986): 163–207.
- David Brink, Moral Realism and the Foundations of Ethics (Cambridge, 1989).
- Philippa Foot, Natural Goodness (Oxford, 2001).
- Rosalind Hursthouse, On Virtue Ethics (Oxford, 1999).
- Michael Thompson, Life and Action (Harvard, 2008) — the logic of the life-form.
- Christine Korsgaard, The Sources of Normativity (Cambridge, 1996).
- Simon Blackburn, Ruling Passions (Oxford, 1998); Allan Gibbard, Wise Choices, Apt Feelings (Harvard, 1990).
- David Enoch, “Agency, Shmagency,” The Philosophical Review 115:2 (2006): 169–198 — the objection to constructivism.
- SEP entries: “Moral Non-Naturalism,” “Naturalism in Metaethics,” “Constructivism in Metaethics.” https://plato.stanford.edu