For determining the order of Plato's works there is little help either from external sources or internally. Regarding the former, the only information likely to be reliable is Aristotle's statement, that the Laws was written after the Republic. This is repeated by Diogenes Laertius (3.37) and Olympiodorus (Prol. 6.24), who add that it was still on wax tablets when Plato died and was published posthumously by one of his students, Philip of Opus. As for internal evidence, cross-references in the Sophist and Politicus3 indicate the prior composition of the former, while the Timaeus mentions the Critias as its sequel. Rather less definite is the apparent reference in the Timaeus (17b–19b.) to the Republic, in the Sophist to the Parmenides and Theaetetus and in the Theaetetus to the Parmenides (183c). There is one other important piece of evidence: in the introduction to the Theaetetus (143c) Plato renounced his use of the reported dialogue form with a clear indication that the use of introductory formulae, such as καὶ ἐγὼ εἶπον, and of interlocutor's replies was becoming a nuisance. It seems unlikely, therefore, that any of his works written in this form are later than the Theaetetus.

In the eighteenth and the first half of the nineteenth century attempts to solve this problem of chronology were based on an interpretation of the dialogues’ contents followed by the formulation of a line of development for Plato's thought. Unsurprisingly the subjective nature of this approach led to a considerable discrepancy between the conclusions of the various scholars.