What Is the Symmetry Argument?

Quick Answer

The symmetry argument is an ancient Epicurean argument, elaborated by Lucretius, designed to dissolve the fear of death. Its core claim is that the nonexistence that follows death is symmetrical with the nonexistence that preceded birth — and since no one regrets the eternity before they were born, rationality requires that we not fear the eternity after we die. The argument has a powerful intuitive grip: when we think about it, the vast stretch of time before our birth does not bother us, so why should the vast stretch after our death? Epicurus deployed the argument as part of his therapy of the fear of death; Lucretius gave it its most famous formulation in Book III of De Rerum Natura: "Look back at the time before our birth. In this way nature holds up to us a mirror of the time that will be after our death." Thomas Nagel challenged the argument in "Death," arguing that the two nonexistences are not genuinely symmetric: before birth we had no life to lose, but after death we have lost a life — and a life we had reason to want to continue. Derek Parfit approached the question through the theory of personal identity, arguing that what matters in survival is psychological continuity, which changes how we should think about the comparison. This page is a philosophical and educational discussion; it is not medical or psychological advice.

Historical Background

The symmetry argument is one of the oldest arguments in the philosophy of death. Epicurus's Letter to Menoeceus contains its seed: since death is nothing to us, the wise person neither fears it nor longs for it. Lucretius, in the first century BCE, made the argument explicit in De Rerum Natura Book III, addressing the fear of death directly. His version has two strands. The first is the mirror argument: the time before our birth is like a mirror held up to show us the time after our death — and since the former does not disturb us, the latter should not either. The second is the "no new sensation" argument: death brings no new experiences, and the dead have no interests that can be frustrated, so death is not a harm. The argument was revived in the twentieth century as the Epicurean tradition was reassessed by analytical philosophers. Thomas Nagel's "Death" (1970) gave the argument its modern formulation and its most influential criticism; the debate continues in the work of Steven Luper, Fred Feldman, Derek Parfit, and others. The argument is also studied in contemporary psychology, where the asymmetry between our attitudes toward past and future nonexistence is investigated as a distinctive feature of the human mind.

Key Arguments

Lucretius's mirror argument. The argument is a comparison. Consider the infinite time before you were born: you do not regret it, mourn it, or fear it. Now consider the infinite time after you die: you fear it. But the two are alike in every relevant respect — both are periods of nonexistence, both contain no experiences, and neither can be worse or better for you than the other. Since our attitudes toward the two periods are inconsistent, rationality requires revising one of them — and since no one can bring themselves to regret prenatal nonexistence, we should stop fearing posthumous nonexistence. The argument aims not to show that death is good but that it is not to be feared.

Nagel's asymmetry objection. Thomas Nagel argues that the comparison fails because the two nonexistences stand in different relations to a life. The nonexistence before birth is followed by a life that will contain goods; the nonexistence after death is preceded by a life whose goods have been cut short. We value life as something to be lived forward, and the loss of future goods is a genuine harm even if it is not experienced. On this view, the symmetry argument trades on an ambiguity: prenatal and posthumous nonexistence are alike as states, but different as losses. What we fear about death is not the state of nonexistence but the loss of the life we would otherwise have had — and that loss has no counterpart before birth.

Parfit and the continuity of the self. Derek Parfit's contribution is to ask what the comparison presupposes. If what matters in survival is psychological continuity rather than identity — as Parfit argues in Reasons and Persons — then the symmetry argument must be evaluated differently. The fear of death is bound up with the sense that "I" will cease to exist; but if the self is a complex of psychological relations, the question of what is lost at death is a question about which relations are severed. Parfit's account does not simply refute the symmetry argument; it relocates the debate from the metaphysics of nonexistence to the ethics of what matters in survival.

The scope of the argument. Even proponents concede that the symmetry argument, if successful, removes the fear of death as a state — but not the fear of dying, which can be a painful process, and not grief, which is a response to the loss of another person's life. The argument targets the existential dread of one's own annihilation, and its success depends on whether we find the mirror comparison compelling. The fact that the argument has been debated for two thousand years is itself evidence that the human relationship to death is not exhausted by reasoning.

Contemporary Relevance

The symmetry argument continues to shape both philosophy and psychology. Philosophers of death still test their accounts of death's badness against it: any theory that says death is a harm must explain what the symmetry argument gets wrong. Psychologists and neuroscientists study the "past-future asymmetry" in human attitudes, exploring why we dread future nonexistence more than past nonexistence and whether this asymmetry is rational. In practical terms, the argument is a resource for those who struggle with the fear of death: it offers a way of deflating the dread of annihilation by comparison with the prenatal state. But it is not a therapy, and philosophers are careful not to prescribe attitudes: whether one finds the argument liberating or question-begging is itself a fact about one's relationship to mortality. This page is educational and philosophical; for persistent death anxiety or grief, qualified professionals should be consulted.

Related Topics

• Is Death Bad for the Person Who Dies? — the wider debate over death and harm.
• Is Death an Evil? — the classical question of death's badness.
• What Is the Deprivation Account of Death? — Nagel's positive alternative to Epicureanism.
• Why Do We Fear Death? — the psychology and philosophy of death anxiety.
• What Is the Philosophy of Death? — the field as a whole.

Sources

1. Stanford Encyclopedia of Philosophy, Death.
2. Thomas Nagel, Mortal Questions (Cambridge University Press, 1979), "Death."
3. Lucretius, De Rerum Natura, Book III (trans. A. E. Stallings, Penguin, 2007).
4. Derek Parfit, Reasons and Persons (Oxford University Press, 1984).