Peter Unger — Radical Skepticism, Empty Ideas, and the Demands of Ethics (1942– )

Peter Unger is an American philosopher and longtime professor at New York University whose career has been defined by an unusual willingness to follow arguments to conclusions that most philosophers find either too radical to accept or too uncomfortable to act on.

A student of A.J. Ayer at Oxford and a contemporary of David Lewis at Swarthmore, he has produced over five decades a body of work spanning epistemology, metaphysics, ethics, and the philosophy of mind that challenges not only specific philosophical positions but the intellectual respectability of analytic philosophy itself.

His central concern across his career: that philosophy should mean what it says — that if an argument is valid and its premises are true, the conclusion follows regardless of how uncomfortable it is, and that the habit of tailoring conclusions to fit prior intuitions is philosophy's most persistent and most corrupting failure.

Ignorance — The Case for Radical Skepticism

In "Ignorance" (1975), Unger argues that nobody knows anything and even that nobody is reasonable or justified in believing anything. This was not a cautious or qualified skepticism — it was the most thoroughgoing skeptical position defended with rigorous argument in twentieth century philosophy.

His argument proceeded from an analysis of knowledge — arguing that knowledge requires certainty, that certainty requires the elimination of all possibility of error, and that no human being is ever in a position to eliminate all possibility of error about anything. Therefore no one knows anything. The conclusion extended further: if no one knows anything, then no one has any reason or justification for any belief, and the entire structure of epistemic evaluation — more and less reasonable, better and worse supported — collapses along with knowledge itself.

The argument drew an enormous response — decades of papers arguing that knowledge does not require certainty, that the relevant standard of certainty is context-dependent, that Unger's analysis was too demanding. These responses gave rise to contextualism about knowledge — one of the most productive developments in late twentieth century epistemology — which Unger himself came to develop and then criticize. His skeptical argument had generated a research program by being wrong in the right way.

"Not only can nothing ever be known — no one can ever have any reason at all for anything. This follows from the nature of knowledge and justification, however uncomfortable it may be."

Living High and Letting Die — The Uncomfortable Ethics

Unger's most widely read work was his 1996 contribution to the literature on global poverty and moral obligation — a work that applied the same uncompromising logical method to practical ethics with similarly unsettling results.

Building on Peter Singer's argument that affluent people have a moral obligation to give substantially to reduce global suffering, Unger argued with detailed thought experiments and case analyses that our intuitive resistance to this obligation was psychologically explicable but morally indefensible. We feel more obligated to help a child drowning in front of us than to donate to save a child dying of preventable disease in another country — but the moral difference between these cases, he argued, was negligible or nonexistent. The spatial and perceptual distance that makes the distant child feel less urgent is morally irrelevant.

He pushed the conclusion further than Singer — arguing that the obligation extended to giving all but what was necessary for survival, and even to begging, borrowing, or stealing for the cause if one's own resources were exhausted. Most readers found this conclusion untenable. Unger's response was that finding a conclusion untenable was not the same as having an argument against it.

"Our intuitions about distant suffering are not moral data — they are psychological facts about the limits of human empathy at a distance. The argument does not care about those limits."

The Problem of the Many and Mereological Nihilism

Unger's work in metaphysics has been as uncompromising as his epistemology and ethics. His 1980 paper "The Problem of the Many" identified a deep puzzle about ordinary objects — that any apparently single object is surrounded by vast numbers of slightly different collections of matter, each of which has equal claim to be that object. How many clouds are there in a cloudy sky? The answer depends on where we draw the boundaries — and there is no principled reason to draw them at any particular place rather than any other. This implies either that there are vastly more objects than we think or that ordinary objects do not exist in the way we assume.

Unger was drawn toward the latter conclusion — mereological nihilism, the view that composite objects do not really exist, only the fundamental particles that compose them. Tables, chairs, and human bodies are not genuine objects but convenient ways of talking about arrangements of simpler things. This led him to the remarkable conclusion that he himself, as a composite object, did not strictly speaking exist — a conclusion he accepted with the equanimity of someone who has been following arguments for a long time and has learned not to be surprised by where they end up.

"If mereological nihilism is true, then I do not exist — or at least nothing answering to my ordinary description exists. This is uncomfortable, but the argument seems sound."

All the Power in the World — The Return to Dualism

Unger's 2006 metaphysical work took an unexpected turn — arguing for a form of Cartesian substance dualism that most analytic philosophers had long considered decisively refuted. He proposed that the correct metaphysics involved two kinds of fundamental particulars: physical entities with powers to interact causally, and immaterial souls with powers for genuine choice and conscious experience.

His argument was that physicalism — the view that everything, including consciousness and choice, is ultimately physical — was incompatible with real agency. If you are wholly composed of physical parts whose interactions are governed by physical laws, then you have no genuine power of choice — your "decisions" are determined by prior physical states. Only an immaterial soul, exempt from physical determination, could be a genuine agent capable of real choice.

The argument surprised readers who had followed his earlier skepticism — a move from "nothing can be known" to "the soul is real and immaterial" seemed an unexpected trajectory. Unger's response was characteristically direct: he had followed the arguments where they led, and they had led here.

"It is only a purely mental particular — an immaterial soul, like yourself — that is ever fit for real choosing or for conscious experiencing."

Empty Ideas — The Indictment of Analytic Philosophy

In "Philosophical Relativity" (1984), Unger argues that many philosophical questions cannot be definitively answered. His 2014 "Empty Ideas" extended this critique into a full-scale indictment of contemporary analytic philosophy — arguing that most of what had passed for philosophical progress since the mid-twentieth century consisted of "concretely empty ideas": propositions that were analytically or definitionally true but said nothing substantial about the actual nature of the world.

The externalism of Putnam and Davidson, the essentialism of Kripke, the possible worlds framework of Lewis — Unger argued that these and most other celebrated contributions to recent analytic philosophy were either trivially true by definition or merely parochial claims about how we use words, not genuine discoveries about concrete reality. With the exception of Lewis's thesis of a plurality of concrete worlds, he found almost nothing in recent mainstream philosophy that constituted genuine progress in understanding the world.

The book was received with a mixture of irritation and respect — irritation because it dismissed the life's work of some of the most celebrated philosophers of the era, respect because the arguments, however uncomfortable, were serious and not obviously wrong.

"Except when offering perfectly parochial ideas, mainstream philosophy still offers hardly anything except for just so many concretely empty ideas."

Legacy — The Philosopher Who Means It

Unger's career is one of the more unusual in contemporary philosophy — a series of positions, each argued with rigorous seriousness, that taken together seem almost to form a reductio of the discipline itself: nobody knows anything, ordinary objects don't exist, the soul is real but you don't exist, and most of what analytic philosophy has achieved in the past fifty years amounts to nothing substantive.

What makes this more than mere provocation is the consistent quality of the arguments. Unger's skeptical argument in "Ignorance" was taken seriously enough to generate contextualism. His poverty argument in "Living High and Letting Die" is one of the strongest cases for demanding moral obligations in the literature on global ethics. His problem of the many remains one of the sharpest puzzles in the metaphysics of ordinary objects. He is wrong in interesting ways — or right in uncomfortable ones.

On CivSim he sits alongside Clifford and Carnap — philosophers who refused to let conclusions be softened by the discomfort of those who would have to live with them, and who insisted that intellectual honesty meant following arguments rather than managing their implications. His career is a sustained demonstration that philosophy done without self-protective hedging leads to some very strange places — and that those places are worth visiting even if one cannot stay.

"The habit of tailoring conclusions to fit prior intuitions is philosophy's most persistent failure — and its most comfortable one."