The Works of Dionysius the Areopagite, tr. by John Parker, [1897], at sacred-texts.com
LETTER VI. To Sopatros 72 --Priest.
Do not imagine this a victory, holy Sopatros, to have denounced 73 a devotion, or an opinion, which apparently is not good. For neither--even if you should have convicted it accurately--are the (teachings) of Sopatros consequently good. For it is possible, both that you and others, whilst occupied in many things that are false and apparent, should overlook the true, which is One and hidden. For neither, if anything is not red, is it therefore white, nor if something is not a horse, is it necessarily a man. But thus will you do, if you follow my advice, you will cease indeed to speak against others, but will so speak on behalf of truth, that every thing said is altogether unquestionable.
145:72 Acts xx. 4; Rom. xvi. 21.