Even those who seem to be "devils," derive their existence from the Good, and are naturally good, and desire the Beautiful and Good in desiring existence, life, and consciousness, ... And they are called evil through the deprivation and the loss whereby they have lapsed from their proper virtues. Hence they are evil only insofar as they lack [true] existence; and in desiring evil, they desire non-existence.
... Even so, we say that the air is darkened around us by a deficiency and absence of the light; while yet the light is itself always light and illumines the darkness. Therefore, evil inheres not in the devils or in us, as evil, but only as a deficiency and lack of the perfection of our proper virtues.
Thus evil has no being, nor any inherence in things that have being. Evil is nowhere qua evil; and it arises not through any power but through weakness. ... in a word, evil is weakness, impotence, and deficiency of knowledge...
~ Dionysius the Areopagite
Reply from leoj99
As good arises in your thoughts evil arises too because they exists as the contrast. How can there be just light without conrast.
Drop your thoughts and both good and evil cancels out.
Reply from Joe Chip
Drop your pants. Dionysius is talking about intuitive knowledge.