And for the
same reason, although these general things, to with, [a body],
eyes, a head, hands, and such like, may be imaginary, we are
bound at the same time to confess that there are at least some
other objects yet more simple and more universal, which are
real and true; and of these just in the same way as with
certain real colours, all these images of things which dwell
in our thoughts, whether true and real or false and fantastic,
are formed.
To such a class of things pertains corporeal nature in
general, and its extension, the figure of extended things,
their quantity or magnitude and number, as also the place in
which they are, the time which measures their duration, and so
on.
That is possibly why our reasoning is not unjust when we
conclude from this that Physics, Astronomy, Medicine and all
other sciences which have as their end the consideration of
composite things, are very dubious and uncertain; but that
Arithmetic, Geometry and other sciences of that kind which
only treat of things that are very simple and very general,
without taking great trouble to ascertain whether they are
actually existent or not, contain some measure of certainty
and an element of the indubitable.
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