2 adverbs to describe how to cogent

One of his arguments, in favour of a common learned language, was ludicrously cogent: "Consider, sir, how you should feel, were you to find, at Rotterdam, an epitaph, upon Erasmus, in Dutch!"

To my mind it would need external proof of an unusually cogent description to render plausible the theory that the year, say, of the Shepherd's Calender saw the appearance of such lines as: What lack I now but an imperiall throne, And Ariadnaes star-lyght Diadem? (II. i.) or:

2 adverbs to describe how to  cogent  - Adverbs for  cogent