HISTORY OF PHILOSOPHY

as true all propositions which manifest themselves in clear and dis
tinct light before the reason. Here belong, firstly, all truths of
mathematics, but here belongs also the ontological proof for the
existence of God. For with the same necessity of thought thus
Descartes takes up Anselm s argument 1 with which the geometri
cal propositions with regard to a triangle follow from the definition
of the triangle, it follows from the mere definition of the most Real
being that the attribute of existence belongs to him. The possibility
of thinking God suffices to prove his existence.
In this way it follows from the criterion of clearness and distinct
ness, that of finite things also, and especially of bodies, so much can
be known as is clearly and distinctly perceived. But this is for
Descartes the mathematical element, and is limited to the quantitative
determinations, while all the sensuous-qualitative elements in percep
tion are regarded by the philosopher as unclear and confused. On this
account metaphysics and the theory of knowledge terminate for him,
too, in a mathematical physics. He designates 2 the sensuous appre-
1 Med. V. 2 Med. VI.
394 The Renaissance : Natural Science Period. [PAKT IV.
hension of the qualitative, "imagination" (imaginatio). The appre
hension of that which can be mathematically constructed he terms, on
the other hand, "intellectual" knowledge (intellectio) , and strongly as
he knows how to prize the help which experience gives in the former,
a really scientific insight rests, in his opinion, only upon the latter.
The distinction between distinct and confused presentations
(which goes back to Duns Scotus and farther) serves Descartes
also to solve the problem of error, which results for him out of his
principle of the veracitas dei, because it does not seem possible to
see how, in accordance with that principle, perfect deity could so
arrange human nature as to allow it to err at all. Here Descartes
helps himself 1 by a peculiarly limited doctrine of freedom, which
might be consistent with either Thomistic determinism or Scotist
indeterminism. It is assumed, that is, that only clear and distinct
presentations exercise so cogent and compelling a power upon the
mind that it cannot avoid recognising them, while with reference to
the unclear and confused presentations it retains the boundless and
groundless activity of the liberum arbitrium indijfer entice (its farthest-
reaching power, which in the Scotist fashion is set in analogy with
the freedom of God). Thus error arises when affirmation and nega