Nicene and Post-Nicene Fathers, Vol. IV:
Writings in Connection with the Manichæan Controversy.: Chapter 18

Chapter 18.—The Understanding Judges of the Truth of Things, and of Its Own Action.

What, then, must be said of the power of perceiving truth, and of making a vigorous resistance against these very images which take their shape from impressions on the bodily senses, when they are opposed to the truth?  This power discerns the difference between, to take a particular example, the true Carthage and its own imaginary one, which it changes as it pleases with perfect ease.  It p. 138 shows that the countless worlds of Epicurus, in which his fancy roamed without restraint, are due to the same power of imagination, and, not to multiply examples, that we get from the same source that land of light, with its boundless extent, and the five dens of the race of darkness, with their inmates, in which the fancies of Manichæus have dared to usurp for themselves the name of truth.  What then is this power which discerns these things?  Clearly, whatever its extent may be, it is greater than all these things, and is conceived of without any such material images.  Find, if you can, space for this power; give it a material extension; provide it with a body of huge size.  Assuredly if you think well, you cannot.  For of everything of this corporeal nature your mind forms an opinion as to its divisibility, and you make of such things one part greater and another less, as much as you like; while that by which you form a judgment of these things you perceive to be above them, not in local loftiness of place, but in dignity of power.