Greek philosophy began in the 6th century BCE with the Presocratics. Rebelling against mythic cosmology, they relied on reason to explain nature's order. So also did Socrates and Plato, but the subjects of their analyses remained primarily within the human domain. Instead of asking, like Thales and Democritus, what element was common to all objects, they posed epistemological and ethical questions, such as: How do we know what we know? What is love? What is virtue? What are the duties of a citizen to the state, and of a ruler to his subjects? What is the soul and how is it psychologically constituted?
Relevant to all these questions, and the underpinning to Plato’s philosophy, was the dichotomy he saw between the material world and the world of Forms: the material world was an illusion, imperfect, and subject to change; that of Forms was immutable, perfect, and the repository of Truth. Boldly he went further by claiming that Forms existed independently of their objects: if you see a tree, you not only see the form of a tree but also experience the forms of height, color, hardness, etc. In tandem with material forms are forms of abstraction, such as Courage, Beauty, and Goodness. Our attempts to capture their essence--on a battlefield or on a canvas--are invariably futile.
To separate truth from falsehood, Socrates devised a pedagogical tool that continues to be popular in law and many other disciplines: the Socratic method. Instead of stating a proposition (e.g., “Virtue is moderation in all things”), then defending it, Socrates begins with an open ended question, such as “Can Virtue be taught?” His collocutors attempt an answer, but Socrates reveals its flaws. A second attempt is made, and it too fails. This process, the dialectic, is repeated several times until one of two outcomes occurs: either an unassailable answer is found, or the characters in the dialogue reach aporia, admitting there is no solution. What makes Plato’s dialogues so noteworthy is that Socrates’s argumentation is usually impeccable and its linear progression easy to follow; the format also is unusual, not stiffly prosaic but dramatic, rife with conflict and characters having distinctive personalities.
The three dialogues we will discuss--Theaetetus, Parmenides, and Sophist--are concerned with epistemology. They address a variety of questions having to do with true knowledge, such as: To what extent do the senses provide reliable information? Is the theory of Forms incoherent and contradictory–how can a Form be a unified whole yet also be a part separate from itself? If Heraclitus's theory of flux is true, then how can we have any knowledge, since the moment we have that knowledge it too will be in flux? Do Sophists convey original ideas or do they imitate what others have said?
Any edition of Plato's works is acceptable. Translations by Benjamin Jowett are often reprinted and inexpensive; however, having been written during the Victorian period, they sometimes sacrifice linguistic accuracy for the sake of propriety. If you think you'll want to continue reading more of Plato and are not deterred by the price, the standard English edition of Plato is now Plato: Complete Works . Edited by John M. Cooper and D. S. Hutchinson. Hackett Publishing Company, 1997 (available from amazon.com for $47.44 new and from $34.66 used). Also acceptable is The Collected Dialogues of Plato Including the Letters. Ed. Edith Hamilton and Huntington Cairns. Princeton University Press, 1961. (available from amazon.com for $37.98 new and from $13.76 used). Slightly lowers prices can be found at bookfinder.com. For those who prefer free public domain copies of the dialogues, click here or here.
The following resources provide analyses, bibliographies, lecture notes, and videos.
Wikipedia: “Plato”, “Socrates”, “Socratic Problem”, “Socratic Method“, “Platonic Epistemology”, “Theory of Forms”, “Problem of Universals”, “Platonic Realism”, “Platonism”, “Theaetetus (dialogue)”, “Parmenides (dialogue)”, “Sophist (dialogue)”, “Sophism”, "List of Speakers in Plato’s Dialogues”
Stanford Encyclopedia of Philosophy: “Socrates”, “Plato”, “Method and Metaphysics in Plato's Sophist and Statesman”, “Plato on Knowledge in the Theaetetus”, “Plato’s Parmenides”
Internet Encyclopedia of Philosophy: “Plato”, "Universals", “Theaetetus”, “The Sophists”
Plato Quotations: The European Graduate School. "Plato-Quotes"; The MacTutor History of Mathematics Archive. "Quotations by Plato"
Lloyd P. Gerson. “What is Platonism?” Journal of the History of Philosophy 43 (2005), pp. 253-276.
Lloyd P. Gerson. “Platonism and the Invention of the Problem of Universals .” Archiv für Geschichte der Philosophie 87 (2004), pp. 1-26.
Samuel C. Wheeler III. “Plato’s Enlightenment: The Good as the Sun.” History of Philosophy Quarterly 14. 2 (April 1997), pp. 177-188.
European Graduate Scbool. "Plato. Theaetetus" and "Plato: Sophist." (contains introduction and analysis followed by the full text of the dialogues)
Samuel C. Wheeler III. “The Conclusion of the Theaetetus.” History of Philosophy Quarterly 1.4 (October 1984), pp. 355-367.
Catherine Osborne. “Knowledge is Perception: In Defense of Theaetetus.” In Ideal and Culture of Knowledge in Plato. Ed. Wolfgang Detel. Franz Steiner Verlag, 2003: 133-158.
Graham Priest. “The Parmenides: A Dialetheic Interpretation.” PLATO: The Electronic Journal of the International Plato Society 12 (2012), pp. 1-63.
Pirmin Stekeler-Weithofer. “Plato and Parmenides on Ideal Truth, Invariant Meaning, and Participation.” Conference Presentation at the Wittgenstein Workshop, University of Chicago. 2003-2004.
Michael J. Hansen. “Plato’s Parmenides: Interpretations and Solutions to the Third Man.” Aporia 20.1 (2010), pp. 65-74. (at time of publication author was a senior majoring in Philosophy at Brigham Young University; this essay placed third in the 2010 David H. Yarn Philosophical Essay Contest)
Christine J. Thomas. "Speaking of Something: Plato's Sophist and Plato's Beard." Canadian Journal of Philosophy 38.4 (December 2008), pp. 631-668.
Fernando Ferrera. "A Two-Worlds, Two-Semantics Interpretation of Plato's Sophist". In Greek Philosophy and Epistemology, volume II (ed. Constantine Boudouris), Ionia Publications 2001, pp. 61-68.
Devin Henry. "A Sharp Eye for Kinds: Plato on Collection and Division." Oxford Studies in Ancient Philosophy 41 (January 2012), pp. 229-55.
Blake E. Hestir. “A ‘Conception’ of Truth in Plato’s Sophist.” Journal of the History of Philosophy 41.1 (2003), pp. 1-24.
“Plato’s Metaphysics.” Powerpoint presentation by Professor Jim Martin, Dept. Of Philosophy, Palomar College.
"The Parmenides" by Professor David Bradshaw, Dept. of Philosophy, University of Kentucky.
"Platonic Forms and the 'Third Man'" by Prof. Sally Haslanger, Dept. of Linguistics and Philosophy, MIT.
"Theaetetus" by Professor Mike Raven, Dept. of Philosophy, New York University.
“The Path of Knowledge: The Theaetetus” by Professor Robert Cavalier, Dept. of Philosophy, Carnegie Mellon University.
"Plato's Epistemology and the Theory of the Forms" by Professor Dennis M. Weiss, Dept. of Philosophy, York College of Pennsylvania.
"Plato’s Theaetetus" (authors' backgrounds unknown).
"Understanding the Third Man Argument" by Professor Taylor Marshall, Dept. of Philosophy, College of Saint Thomas More.
"Bryan Magee Talks to Miles Burnyeat on Plato" Section 1; Section 2; Section 3; Section 4; Section 5.
"Plato in 90 Minutes" by Paul Strathern" Part 1; Part 2; Part 3; Part 4; Part 5; Part 6; Part 7.
“An Introduction to Plato’s Dialogues”; "Plato's Forms"; "Final Reflections on Plato" by Professor David Roochnik, Dept. of Philosophy, Boston University.
"Third Man Argument" (a succinct, one minute explanation; author unknown).