Is Knowledge Just Perception? — Plato’s Theaetetus (Lecture 1)

Lecture 1 of "Plato’s Theaetetus: An Inquiry into Knowledge." Watch the full lecture series: Plato’s Theaetetus: An Inquiry into Knowledge Presented by Ergo, a nonprofit that publishes structured philosophical lectures online, free to anyone. https://ergo.org About this lecture In this opening lecture of a course on Plato's Theaetetus, Richard Polt guides viewers through one of philosophy's most entertaining and enduring dialogues. He begins by addressing the challenge of reading Plato, a writer who never speaks in his own voice, and the paradox of a philosopher who distrusted writing yet produced some of the greatest texts in history. Polt then walks through the prologue's themes of death, character, and everyday knowledge before introducing the dialogue's central question: what is knowledge? Along the way, he unpacks Socrates' role as intellectual midwife, the difference between giving examples and offering definitions, and the problem of circular reasoning. The lecture builds toward the first major answer proposed in the dialogue: that knowledge is perception, connecting it to Protagoras' relativism and even modern physics. Polt shows why this ancient conversation still matters for anyone trying to understand what it means to truly know something. About this course Richard Polt leads a five-lecture exploration of Plato's Theaetetus, one of philosophy's most fascinating dialogues. The course takes up the fundamental question: what is knowledge? Theaetetus’s first proposal is that knowledge is simply perception. Polt traces how Socrates connects this idea to the relativism of Protagoras and the flux theory of Heraclitus, then dismantles it through arguments about expertise, self-refutation, and the role of the soul in grasping concepts. The inquiry shifts from perception to judgment, ending without a final answer. No prior background in philosophy is needed. About Richard Polt Richard Polt is a Professor of Philosophy at Xavier University. He holds a B.A. in philosophy from the University of California at Berkeley and a Ph.D. from the Committee on Social Thought at the University of Chicago. His interests include German and Greek philosophy, and he has taught courses on Heidegger, memory, history, technology, and African-American philosophy. Polt's publications include Heidegger: An Introduction, The Emergency of Being: On Heidegger's Contributions to Philosophy, and Time and Trauma: Thinking Through Heidegger in the Thirties. He has also edited or co-edited volumes including A Companion to Heidegger's Introduction to Metaphysics, Heidegger's Being and Time: Critical Essays, After Heidegger?, and The Task of Philosophy in the Anthropocene. Chapters 00:00 Welcome to the Course on Plato's Theaetetus 01:47 How to Read Plato When He Never Speaks 03:52 Why Plato Thought Writing Was Dangerous 07:24 The Paradox of Writing About Writing's Futility 10:15 The Prologue: Death and Character 12:14 Knowledge in Everyday Life Before Philosophy 14:40 Socrates Meets His Ugly Double 16:37 Is Wisdom the Same as Knowledge? 19:24 Examples Are Not Definitions 20:51 The Clay Analogy and Circular Definitions 23:46 Irrational Numbers and the Limits of Language 26:16 Socrates the Intellectual Midwife 30:28 Knowledge Is Perception — The First Answer 34:08 Protagoras and the Measure of All Things 37:57 Ancient Relativism Meets Quantum Mechanics 39:11 Why Perception Destroys Absolute Reality