418. Philosophical Teaching. -- The three books of his great work, De Docta Ignorantia, are devoted respectively to God, or the Infinite; the universe and man, or the finite; and God the Redeemer, or the union of finite and Infinite. The influence of Neo-Platonism on the theories of Nicholas of Cusa was profound and far-reaching: he is much nearer Plotinus and Proclus than Witelo and Theoderic of Freiburg were in the thirteenth century.

The theosophical lines on which he establishes relations between philosophy and theology are likewise in keeping with his Neo-Platonic sympathies. His teaching is borrowed from the theosophy of Lully (355). On the one hand, the light of faith is indispensable for the discovery of truth (spiritus veritatis et virtus illuminativa caeci nati qui per fidem visum acquirit): without it the human spirit is like one born blind. On the other hand, reason is but a blossoming of faith, and can therefore attain to a demonstrative knowledge of mysteries. To get fully at the mind of Nicholas we must put this theosophical theory into relation with the mysticism of the Docta Ignorantia.

Our knowledge of God is negative. We cannot describe as truth either sense knowledge (sensus), or abstract, rational knowledge (ratio) based on the former, for both alike are changeable and fragmentary. Intellect alone, sustained by the supernatural aid of grace, can raise us up to the one, immutable Truth, which is God. Then we can understand how the Infinite is impenetrable and unknowable to us. And this consciousness of our own ignorance constitutes true wisdom, Docta Ignorantia: which should be made the basis of a new and negative theology to take the place of the false and misleading speculations of the current or positive theology (cf. Pseudo-Denis, 105).

Whilst reason often arrives at divergent or contradictory conclusions, intellect attains to the intuition of the Divine Unity. In God, all contradictories will be found to merge and coincide (coincidentia oppositorum). Borrowing copious analogies from mathematics, Nicholas compares this coincidence of contradictories with the curve that becomes a straight line by lessening the curvature indefinitely, or with the hypotenuse which coincides with the other two sides of a triangle when the angle between the latter is increased indefinitely. God, says Nicholas, is infinitely great, and therefore, since He could not be any less than He is (!), He is likewise infinitely small. Excluding from His being everything opposed to Himself, God is the sole being; He is the complicatio omnium: in Him are all the manifold beings of the universe reduced to unity. Man can have positive knowledge of no essence whatsoever, because he can have no positive knowledge of God, Who contains them all. Consequens est omnem humanam veri positionem esse conjecturam. Here we touch the fundamental error of Nicholas's teaching: the theory he borrowed from the German mystics -- who certainly influenced his philosophy profoundly -- that God is a sort of consubstantial substratum or subsoil into which the whole universe plunges its roots. The universe contains explicitly what God contains implicitly; or, to make use of an appropriate and time-honoured expression, things are but Divine theophanies. Is the Catholic cardinal then a pantheist, like Scotus Eriugena, whose terminology he adopts, or like David of Dinant, for whom he does not conceal his sympathies? He defends himself vigorously against the charge in his Apologia Doctae Ignorantiae, against a certain VENCHUS who had attacked him and accused him of heresy. But we may say of him as of Eckhart, that he preserved his orthodoxy only at the expense of his logic, and that it was only by a deliberate effort he repressed the natural conclusions from his premisses.

About the created universe, Nicholas taught that God created matter, or being in potency, but that matter cannot exist as such, that it needs a substantial form (286). And when he had described God as the form of all things, actus omnium, he added, in order to avoid pantheism, that God is in the creature only as the prototype of the latter, not as identical with its reality. Man is the centre of creation and the most perfect image of God, for he embodies the universe in a manner within himself, by the mental representation he forms of it: as God also sums up in Himself the reality of all created things.

In the main lines of his psychology Nicholas is scholastic: the soul, the substantial form of the body, is spiritual and immortal (303). Our abstract cognitions have their origin in sense knowledge; but above reason there is intellect, which puts us into contact with the supreme Truth. In this exalted vision of things, wherein all the contradictions of human science are resolved, the union of the soul with God is so intimate that it is a sort of deification.