Full Idea
The main basic principle of the sceptic system is that of opposing to every proposition an equal proposition.
Gist of Idea
The basis of scepticism is the claim that every proposition has an equal opposing proposition
Source
Sextus Empiricus (Outlines of Pyrrhonism [c.180], I.12)
Book Reference
Sextus Empiricus: 'Outlines of Pyrrhonism', ed/tr. Bury,R.G. [Prometheus 1990], p.19