The Megarians flourished during the fourth and the early third centuries BCE. They derived their name from their connection with Megara on the Isthmus (a city one day's walk west of Athens). They constituted a 'philosophical school' only in a weak sense: no shared lifestyle, no rigid body of doctrine. Since no work of any Megarian has survived, knowledge of them must rely on fragments and reports of other authors.

The earliest Megarian was Euclides of Megara. Diogenes Laertius (2.106) reports that Euclides' followers "were called 'Megarians,' then 'Eristics,' and later 'Dialecticians.'" Modern scholars traditionally understood this report as indicating that a single school had three successive labels. However, in 1977 David Sedley argued that the three labels designated three distinct groups of philosophers that were influenced to some extent by Euclides but, far from constituting a single school, were in competition with one another. Sedley's reconstruction...