_Grundzüge der Philosophie des Nikolaus Cusanus mit besonderer
Berücksichtigung der Lehre vom Erkennen_, Breslau, 1880. R. Eucken,
_Beiträge zur Geschichte der neueren Philosophie_, Heidelberg, 1886, p. 6
seq.; Joh. Uebinger, _Die Gotteslehre des Nikolaus Cusanus_, Münster,
1888. Scharpff, _Des Nikolaus von Cusa wichtigste Schriften in deutscher
Uebersetzung, Freiburg i. Br_., 1862.]

Human knowledge and the relation of God to the world are the two poles of
the Cusan's system. He distinguishes four stages of knowledge. Lowest of
all stands sense (together with imagination), which yields only confused
images; next above, the understanding (_ratio_), whose functions comprise
analysis, the positing of time and space, numerical operations, and
denomination, and which keeps the opposites distinct under the law of
contradiction; third, the speculative reason (_intellectus_), which finds
the opposites reconcilable; and highest of all the mystical, supra-rational
intuition (_visio sine comprehensione, intuitio, unio, filiatio_),
for which the opposites coincide in the infinite unity. The intuitive
culmination of knowledge, in which the soul is united with God,--since
here even the antithesis of subject and object disappears,--is but seldom
attained; and it is difficult to keep out the disturbing symbols and images
of sense, which mingle themselves in the intuition. But it is just this
insight into the incomprehensibility of the infinite which gives us a true
knowledge of God; this is the meaning of the "learned ignorance," the
_docta ignorantia_. The distinctions between these several stages of
cognition are not, however, to be understood in any rigid sense, for
each higher function comprehends the lower, and is active therein. The
understanding can discriminate only when it is furnished by sensation with
images of that which is to be discriminated, the reason can combine only
when the understanding has supplied the results of analysis as material for
combination; while, on the other hand, it is the understanding which is