Theodorus of Cyrene on Incommensurable Magnitudes

Theodorus of Cyrene, late fifth century BCE, is the name this site attaches to a Greek geometer. Plato’s Theaetetus is the Greek host: Socrates names him as teacher in γεωμετρία, ἀστρονομία, ἀριθμητική, and μουσική.

What this site holds is Testimonies: five passages from that dialogue, on incommensurable sides from 3 to 17. No book of Theodorus survives. Theaetetus’s later generalisation is another name. Euclid book X is a later arrangement. It is quotation in Plato, not an autograph.