The Timaeus comes to us as part of a single huge complex. What remains of the rest is the unfinished Critias, which also mainly consists of a monologue, the ‘history’ of the ancient confrontation of Athens and Atlantis. The Critias is not linked to the Timaeus as a distinct although dramatically sequential dialogue in the way the Sophist (coupled with the Statesman) is to the Theaetetus. The Sophist discussion is assigned dramatically to the day following that of the Theaetetus discussion (Theaetetus 210d3–4; Sophist 216a1–2), and it brings in a major new speaker not present ‘yesterday’. By contrast, the discourses of the Timaeus and Critias unfold on the same day dramatically speaking, and the characters are the same throughout. Plato may not have had the Sophist and Statesman in view at all when he wrote the Theaetetus; stylometry shows that they were written at a later period. By contrast, the Timaeus–Critias from the start was planned and written as a complex unit.
Even in a book devoted mainly to the cosmology, we should try to find a perspective, perhaps more than one perspective, that gives point to the coupling of the Timaeus with the Critias. The presentation of the Athens–Atlantis ‘history’ is so deeply puzzling in so many ways that it may well seem that there is more to be learnt about the Critias than about the Timaeus through looking at them together. And that may indeed be true. Even so, it remains a fact about the cosmology that it is set in the context of Critias’s story, and this fact is a surprising and unsettling one. It should be enough to motivate interpreters of the Timaeus to attempt an explanation.