“Every age has its own outlook,” wrote C. S. Lewis; “We, therefore, need the books that will correct the characteristic mistakes of our own period.” But we need more than that—we need books that reach our conclusions long before we do, books that remind us that our new outlook isn’t so new after all.

We call our times postmodern, often with something like fear. But postmodernism is in large part a renovation of ancient ideas—ideas you should know.

Postmodernists say:

“Right and wrong are human interpretations”

Though moral relativism has a postmodern flavor, it dates back to the ancient Greeks. Plato ascribed it to Protagoras; later, Herodotus assessed other cultures’ customs without questioning their rightness and wrongness. Later yet, Sextus Empiricus determined not that morality is relative to culture, but that moral knowledge is itself impossible.

Is moral relativism postmodern? Yes, in the sense that it exists today; no, in the sense that it’s uniquely characteristic of postmodernism. Before your next debate on moral relativism, you should read Plato, who, fearing moral chaos, argued that morality must be not only in the actor’s self-interest but also based on objective truth.

“But objective truth doesn’t exist!”

We usually trace this postmodern claim back to Nietzsche’s assertion that there are no facts, only interpretations. But it, too, has ancient roots: in the fifth century BC, Protagoras argued that “Man is the measure of all things.” Later, Plato and Socrates clashed with the Sophists over the nature of absolute truth: while the Sophists venerated persuasion and rhetoric, Plato and Socrates responded that the measure of an argument isn’t its persuasiveness, but its truthfulness.

Much later, Kant argued that truth is merely nominal (“true” means something within language), not real—not a statement about a thing’s essence. “Kant drew out the limits of our mind,” said Hegel, “and because of this we can not have a knowledge of the absolute truth.” But Hegel still found a way to truth: his “dialectic,” which, like science, moves from increasingly accurate oppositions—thesis, antithesis—to synthesis, the resolution that best corresponds to what is real.

“What we experience isn’t the world—it’s just our perceptions of the world”

Again we turn to Plato. In The Republic, his Socrates explains that without philosophy, we are like bound prisoners in a cave who, having seen nothing else all our lives, see shadows on the wall and interpret them as real things. Without philosophy, Plato claims, we mistake erroneous perceptions for reality; with philosophy, we see the world as it really is. Around two thousand years later, though, Descartes argued that wax’s physical characteristics reveal nothing about the wax itself: after all, its color, scent, shape, size, hardness, and coldness are all subject to change. George Berkeley took doubt even further, arguing that the world doesn’t even exist: only our perceptions of it do. (Sound postmodern?)

But Thomas Reid rejected that notion in compelling terms, arguing that common-sense belief in the world is the basis for all philosophy—that if you don’t believe in the world as perceived, the conversation is useless.

“We don’t have individual identities or souls”

Postmodernists from Foucault to Lacan to Riceour have argued that personal identity is unstable—that, without any essential “I,” we identify with images or stories to define ourselves. This thesis of shifting (or nonexistent) identity smacks of postmodernity, but it, too, is ancient. Plutarch wrote, in the first century AD, “Dead is the man of yesterday, for he is passed into the man of today . . . Nobody remains one person.” Heraclitus wrote that we cannot step into the same river twice: not only has the river changed; we have, too. Much later, Hume took Berkeley’s claim (“the physical world doesn’t exist”) even further, arguing that not even individuals really exist—we’re nothing but perceivers of perceptions.

But if the claims are old, so are the counterarguments. Spinoza argued that all things do have an essence, and that the nature of that essence is to persist in its being. Descartes argued, famously, that because we think, we exist.

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To engage with our time’s prevailing ideas, you need to know where they come from—you need to know philosophy, both ancient and modern. Noet’s Ancient and Modern Philosophy bundles equip you with the core texts of the Western philosophical tradition: Socrates, Plato, Aristotle, Descartes, Spinoza, Leibniz, Locke, Berkeley, Hume, and Kant.

Pre-order the Ancient and Modern Philosophy bundles today, or build your library with the comprehensive Classical Foundations Bundle—everything you need to understand the origins of Western thought.

Then keep reading—where did history come from?