Plato's unwritten doctrines are metaphysical theories ascribed to him by his students and other ancient philosophers but not clearly formulated in his writings. In recent research, they are sometimes known as Plato's 'principle theory' (German: Prinzipienlehre) because they involve two fundamental principles from which the rest of the system derives.
The main sources ascribing esoteric doctrines to Plato are first-generation members of his Academy, most notably Aristotle. These sources indicate that Plato believed certain parts of his teachings could not be explained in writing in a way that would be accessible to general readers; therefore, he restricted their teaching to students in the Academy.
In the middle of the twentieth century, historians of philosophy initiated a wide-ranging project aiming at systematically reconstructing the foundations of the unwritten doctrines. The group of researchers who led this investigation came to be called the 'Tübingen School' (in German: Tübinger Platonschule), because some of its leading members were based at the University of Tübingen in southern Germany. While its advocates have described the Tübingen reconstruction as a 'paradigm shift' in Plato studies, critics of the Tübingen School have argued that the available evidence is insufficient to establish that Plato deliberately withheld a systematic metaphysical doctrine from his written dialogues.
Key terms
The expression 'unwritten doctrines' (in Greek: ἄγραφα δόγματα, ágrapha dógmata) refers to doctrines of Plato taught inside his school and was first used by his student Aristotle. In his treatise on physics, he wrote that Plato had used a concept in one dialogue differently than 'in the so-called unwritten doctrines.'See below and Aristotle, Physics, 209b13–15. Modern scholars who defend the authenticity of the unwritten doctrines ascribed to Plato lay stress on this ancient expression. They hold that Aristotle used the phrase 'so-called' not in any ironic sense, but neutrally.
The scholarly literature sometimes also uses the term 'esoteric doctrines.' This has nothing to do with the meanings of 'esoteric' common today: it does not indicate a secret doctrine. For scholars, 'esoteric' indicates only that the unwritten doctrines were intended for a circle of philosophy students inside Plato's school (in Greek, 'esoteric' literally means 'inside the walls'). Presumably they had the necessary preparation and had already studied Plato's published doctrines, especially his Theory of Forms, which is called his 'exoteric doctrine' ('exoteric' means 'outside the walls' or perhaps 'for public consumption').For a general discussion of esotericism in ancient philosophy, see W. Burkert, Lore and Science in Ancient Pythagoreanism (Cambridge: Harvard University Press, 1972), pp. 19, 179 ff., etc. On the distinction between esotericism and secrecy in ancient philosophy, see C. S. O'Brien, Plato's Unwritten Doctrines (Cambridge: Cambridge University Press, 2025), pp. 6-7.
Modern advocates of the possibility of reconstructing the unwritten doctrines are often called in a short and casual way 'esotericists' and their skeptical opponents are thus 'anti-esotericists.'For example, in Konrad Gaiser: Platons esoterische Lehre.
The Tübingen School is sometimes called the Tübingen School of Plato studies to distinguish it from an earlier 'Tübingen School' of theologians based at the same university. Some also refer to the 'Tübingen paradigm.' Since Plato's unwritten doctrines were also vigorously defended by the Italian scholar Giovanni Reale, who taught in Milan, some also refer to the 'Tübingen and Milanese School' of Plato interpretation. Reale introduced the term 'protology,' i.e., 'doctrine of the One,' for the unwritten doctrines, since the highest of the principles ascribed to Plato is known as the 'One.'For Reale's research, see Further Reading below.
Evidence and sources The case for the unwritten doctrines involves two steps.See Dmitri Nikulin, ed., The Other Plato: The Tübingen Interpretation of Plato's Inner-Academic Teachings (Albany: SUNY, 2012), and Hans Joachim Krämer and John R. Catan, Plato and the Foundations of Metaphysics: A Work on the Theory of the Principles and Unwritten Doctrines of Plato with a Collection of the Fundamental Documents (SUNY Press, 1990). The first step consists in the presentation of the direct and circumstantial evidence for the existence of special philosophical doctrines taught orally by Plato. This, it is claimed, shows that Plato's dialogues, which have all survived, do not contain all of his teaching, but only those doctrines suitable for dissemination by written texts. In the second step, the range of sources for the supposed content of the unwritten doctrines is evaluated and the attempt made to reconstruct a coherent philosophical system.
Arguments for the existence of the unwritten doctrines
The chief evidence and arguments for the existence of Plato's unwritten doctrines are the following:
Passages in Aristotle's Metaphysics and Physics, especially the one in the Physics where Aristotle explicitly refers to the 'so-called unwritten doctrines.'Aristotle, Physics, 209b13–15. Aristotle was for many years a student of Plato, and it is assumed that he was well-acquainted with the teaching activity in the Academy and thus a good informant. The report of Aristoxenus, a student of Aristotle, about Plato's public lecture 'On the Good.'Aristoxenos, Elementa harmonica 2,30–31. According to Aristoxenus, Aristotle told him that the lecture contained mathematical and astronomical illustrations and Plato's theme was the 'One,' his highest principle. This together with the title of the lecture implies it dealt with the two principles at the heart of the unwritten doctrines. According to Aristotle's report, the philosophically unprepared audience met the lecture with incomprehension.
The criticism of writing in Plato's dialogues (German: Schriftkritik).See ch. 1 of Hans Joachim Krämer and John R. Catan, Plato and the Foundations of Metaphysics: A Work on the Theory of the Principles and Unwritten Doctrines of Plato with a Collection of the Fundamental Documents (SUNY Press, 1990). Many dialogues accepted as authentic are skeptical about the written word as a medium for transferring knowledge and express a preference for oral transmission. Plato's Phaedrus explains this position in detail. There the superiority of oral over written teaching for transmitting philosophy is grounded in the far greater flexibility of oral discourse, which is held to be a decisive advantage. Authors of texts cannot adapt to the level of knowledge and the needs of individual readers. Moreover, they cannot answer readers' questions and criticisms. These are only possible in conversation, which is alive and psychologically responsive. Written texts are mere images of speech. Writing and reading are thought not only to lead to a weakening of our minds, but also to be unsuited for communicating wisdom, which can only succeed in oral instruction. Written words are useful only as reminders for those who already know something but may have forgotten it. Literary activity is therefore portrayed as mere play. Personal discussions with students are essential and may permit words in various individualized ways to be inscribed in the soul. Only those who can teach in this way, the Phaedrus continues, can be considered true philosophers. In contrast, those authors who have nothing 'more precious' (Gk., timiōtera) than a written text, which they have long polished, are only authors or writers but not yet philosophers. The meaning here of the Greek for 'more precious' is debated but is thought to point toward the unwritten doctrines.Platon, Phaedrus 274b–278e. The criticism of writing in Plato's Seventh Letter, whose authenticity is contested, is nonetheless accepted by the Tübingen School. There Plato asserts—if he is really the author—that his teaching can only be communicated orally (at least, he says, that part of it he is 'serious' about). He emphatically says that there is no text capable of expressing his philosophy and never will be, since it cannot be communicated like other teachings. Real understanding in the soul, the letter continues, arises only from intense, common effort and a shared path in life. Deep insights occur suddenly, the way a spark flies up and lights a fire. Fixing thought in writing is damaging since it produces illusions in the minds of readers, who either despise what they do not understand or become arrogant about their superficial learning.Plato, Seventh Letter, 341b–342a. The 'doctrine of reserve' in the dialogues. There are numerous passages in the dialogues in which an especially important theme is introduced but then not further discussed. In many cases, the conversation breaks off just where it approaches the crux of the issue. These often concern questions which are of fundamental significance for philosophy. The defenders of the Tübingen School interpret these instances of 'reserve' as pointers to the content of the unwritten doctrines, which cannot be directly handled in written dialogues.See ch. 7 of Hans Joachim Krämer and John R. Catan, Plato and the Foundations of Metaphysics: A Work on the Theory of the Principles and Unwritten Doctrines of Plato with a Collection of the Fundamental Documents (SUNY Press, 1990). The fact that it was common in antiquity to distinguish between 'exoteric' matters, suitable for open and public discussion, and 'esoteric' matters, suitable only for instruction within a school. Even Aristotle employed this distinction.Hans Joachim Krämer: Die platonische Akademie und das Problem einer systematischen Interpretation der Philosophie Platons. The widespread view in antiquity that the content of Plato's doctrines that had been reserved for oral transmission went significantly beyond the philosophy expressed in the dialogues.See Appendix 3 of Hans Joachim Krämer and John R. Catan, Plato and the Foundations of Metaphysics: A Work on the Theory of the Principles and Unwritten Doctrines of Plato with a Collection of the Fundamental Documents (SUNY Press, 1990). The unwritten doctrines are thought to be the logical consequence of Plato's supposed project of reducing multiplicity to unity and particularity to generality. Plato's Theory of Forms reduces the multiplicity of appearances to the relatively smaller multiplicity of the Forms that are their foundation. Within Plato's hierarchy of Forms, the many lower-level Forms of the species derive from and depend on the higher and more general Forms of each genus. This leads to the supposition that the introduction of Forms was only a step on the way from the maximum multiplicity of appearances to the greatest possible unity. Plato's thought naturally leads therefore to the consequence that the reduction of multiplicity to unity must be brought to a conclusion, and this must occur in the unpublished theory of his highest principles.Michael Erler: Platon, München 2006, pp. 162–164; Detlef Thiel: Die Philosophie des Xenokrates im Kontext der Alten Akademie, München 2006, pp. 143–148.
The ancient sources for the reconstruction
If the Seventh Letter is authentic, Plato sharply disapproved of disclosing the contents of the supposed unwritten doctrines in writing. However, no obligation to remain silent was imposed upon the 'initiated.' The 'esoteric' character of the teachings should not be understood as a requirement to keep them secret or as a ban on writing about them. Indeed, students in the Academy did later publish writings about the unwritten doctrines or reuse them in their own works.SeeMichael Erler: Platon (= Hellmut Flashar, ed.) This 'indirect tradition,' the evidence drawn from other ancient authors, supplies a basis for the reconstruction of doctrines that Plato communicated only orally.