After deny, speak against, doubt, etc., followed by ὡς or ὅτι, a redundant οὐ is often inserted. Thus, ὡς μὲν οὐκ ἀληθῆ ταῦτ᾽ ἐστίν, οὐχ ἕξετ᾽ ἀντιλέγειν
that this is true you will not be able to deny 8.31.
a. Here the ὡς clause is an internal accusative (accusative of content) after ἀντιλέγειν. Originally the meaning seems to have been ‘you will not be able to deny in this way—this is not true’ where οὐ is not redundant.