evil will._
Let no one, therefore, look for an efficient cause of the evil will;
for it is not efficient, but deficient, as the will itself is not an
effecting of something, but a defect. For defection from that which
supremely is, to that which has less of being,--this is to begin
to have an evil will. Now, to seek to discover the causes of these
defections,--causes, as I have said, not efficient, but deficient,--is
as if some one sought to see darkness, or hear silence. Yet both of
these are known by us, and the former by means only of the eye, the
latter only by the ear; but not by their positive actuality,[526] but
by their want of it. Let no one, then, seek to know from me what I know
that I do not know; unless he perhaps wishes to learn to be ignorant of
that of which all we know is, that it cannot be known. For those things
which are known not by their actuality, but by their want of it, are
known, if our expression may be allowed and understood, by not knowing
them, that by knowing them they may be not known. For when the eyesight
surveys objects that strike the sense, it nowhere sees darkness but
where it begins not to see. And so no other sense but the ear can
perceive silence, and yet it is only perceived by not hearing. Thus,
too, our mind perceives intelligible forms by understanding them; but
when they are deficient, it knows them by not knowing them; for "who
can understand defects?"[527]