Thrassylus’ division of the Platonic Corpus into groups of four dialogues (tetralogies).

The standard editions of the Platonic Corpus that we currently use reproduce a canonical arrangement of presentation of the Platonic dialogues. This arrangement, which is also preserved in the oldest extant manuscripts, follows the ancient canonical ordering into tetralogies, that is in groups of four dialogues.

Who was the first to divide Plato’s dialogues into tetralogies remains an open question. According to a later testimony, Plato published (some of) his dialogues on the basis of the model of the theatrical tetralogies that were presented in ancient theater competitions (three tragedies and one satyr play). It is likely that the first attempt to arrange the platonic work occurred in the context of the activity of the Academy, by Plato’s successors.

It seems, however, that the first systematic attempt to arrange the Platonic Corpus was the work of the Alexandrian philologists Aristophanes of Byzantium (3rd century BC). Aristophanes attempted to arrange the Platonic dialogues into trilogies, that is into groups of three dialogues, but for unknown reasons he never completed this task.

The final arrangement of the Platonic dialogues into tetralogies was rather the product of a multiple process which involved, among other things, the edition of the entire Platonic corpus. Among the people that appear in the sources as involved in this process of arrangement, the name of Thrasyllus (1st century B.C.-1st century A.D.) as the inventor of the tetralogies is the one that occurs more often.

We know that Thrasyllus was the personal astrologist of emperor Tiberius. He was a mathematician with a special interest in Pythagorean and Platonic philosophy. He wrote at least two introductory philosophical textbooks, on Plato and Democritus respectively: Prolegomena to the reading of Plato’s dialogues and Prolegomena to the reading of Democritus’ books. In these he included the division of the works of these two philosophers into tetralogies and he may have added a second title in accordance to the topic of each dialogue. It is possible that his was a more systematic treatment based on an earlier source.

The arrangement of Plato’s dialogues according to Thrasyllus is the following:

1st tetralogy:

Euthyphro

Socrates’ Apology

Crito

Phaedo

2nd tetralogy:

Cratylus

Theatetus

The Sophist

The Statesman

3rd tetralogy:

Parmenides

Philebus

Symposium

Phaedrus

4th tetralogy:

Alcibiades

Alcibiades II

Hipparchus

Rival lovers

5th tetralogy:

Theages

Charmides

Laches

Lysis

6th tetralogy:

Euthydemus

Protagoras

Gorgias

Meno

7th tetralogy:

Hippias a

Hippias b

Ion

Menexenus

8th tetralogy:

Clitophon

Republic

Timaeus

Critias

9th tetralogy:

Minos

Laws or o

Epinomis

Letters

The nine tetralogies cover the entire Platonic Corpus, including the letters as well as the spurious or disputed texts. The principle on which the dialogues were organized remains a question of for scholarly research and controversy. The only tetralogy that presents a clear thematic unity is the first, since the four dialogues describe Socrates’ last days and present the model of the life of philosophy.

Two basic interpretations have been proposed for the rest of the tetralogies. According to the first interpretation, the principle of the tetralogical ordering is the philosophical themes of the dialogues. Setting aside the first tetralogy, the remaining eight are grouped as follows: the second and the third tetralogies contain dialogues about knowledge and dialectic, the fourth and the fifth about the method of midwifery and education, the two next tetralogies on sophistic, and the two last ones on political philosophy.

The alternative interpretation is based on the idea of dramatic tetralogies and suggest that in each group the first three dialogues share a common character, while the fourth one varies, just as would be the case in the difference between tragedies and a satyr play. Besides the specific difficulties that each interpretation faces, there are some shared problems: a) their failure to explain the presence of spurious dialogues; and b) the changes both interpretations introduce with respect to the ordering of the dialogues in order to match the suggested scheme.