Is Knowledge Justified True Belief? A Lucky Guess Isn't Knowledge — Plato’s Theaetetus (Lecture 5)

Lecture 5 of "Plato’s Theaetetus: An Inquiry into Knowledge." In this fifth lecture, Richard Polt walks through the final stretch of Plato's Theaetetus, where Socrates and his interlocutors try every available strategy to pin down what knowledge really is. Starting from the problem of false judgment, the discussion moves through the aviary model of memory, the dream theory of perceivable but unknowable elements, and three versions of what it means to give an "account" of something: putting judgment into words, listing elements, and identifying a distinguishing mark. Each attempt collapses under scrutiny. The lecture highlights how spelling a name correctly could be a lucky guess, anticipating the modern Gettier problem that undermines justified true belief. Polt also connects these ancient puzzles to Descartes's self-evident truths, the unity of music and memory, and even questions about AI and learning. The dialogue ends without a definition of knowledge, but Socrates insists this apparent defeat is itself a philosophical victory. Watch the full lecture series:    • Plato’s Theaetetus: An Inquiry into Knowledge   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 Recap: True Judgment and the Wax Block Problem 01:03 The Aviary Model of Memory 02:56 Philosophy as Recollection 04:21 How False Judgment Works in the Aviary 06:18 The Circularity Trap in Explaining Error 09:15 The Jury Counter-Example 10:33 Justified True Belief and the Gettier Problem 13:10 Can Putting Judgment into Words Be Enough? 15:28 Listing Elements as an Account 18:16 The Dream Theory: Perceivable but Unknowable 22:18 The Parts and Wholes Dilemma 26:20 Self-Evidence and the Limits of Analysis 29:57 Descartes and Self-Evident Truths 31:39 Music, Memory, and Temporal Unity 33:56 Account as Distinguishing Mark 35:45 Wind Eggs and Socratic Wisdom 41:22 Snatching Victory from Defeat 44:16 Falsifiability, Learning, and AI Presented by Ergo, a nonprofit that publishes in-depth philosophy courses taught by leading scholars. Every course is freely available. https://ergo.org Connect with Ergo: Subscribe:    / @ergo_org   Instagram:   / ergo_org   LinkedIn:   / ergoorg