Full Idea
The dogmatists ask how the sceptic can show there is no criterion. If without a criterion, he is untrustworthy; with a criterion he is turned upside down. He says there is no criterion, but accepts a criterion to establish this.
Gist of Idea
How can sceptics show there is no criterion? Weak without, contradiction with
Source
Sextus Empiricus (Against the Mathematicians [c.180], 440)
A Reaction
This is also the classic difficulty for foundationalist views of knowledge. Is the foundation justified, or not?
Book Reference
'The Stoics Reader', ed/tr. Inwood,B/Gerson,L.P. [Hackett 2008], p.36