nature has ever actually been so formed, the perception remains
true, and is the easiest manner of conceiving a sphere.
(72:5) We must observe that this perception asserts the rotation
of a semicircle - which assertion would be false, if it were not
associated with the conception of a sphere, or of a cause
determining a motion of the kind, or absolutely, if the assertion
were isolated. (6) The mind would then only tend to the
affirmation of the sole motion of a semicircle, which is not
contained in the conception of a semicircle, and does not arise
from the conception of any cause capable of producing such motion.
(72:7) Thus falsity consists only in this, that something is
affirmed of a thing, which is not contained in the conception
we have formed of that thing, as motion or rest of a semicircle.
(8) Whence it follows that simple ideas cannot be other than
true - e.g., the simple idea of a semicircle, of motion, of rest,
of quantity, &c.
(72:9) Whatsoever affirmation such ideas contain is equal to the
concept formed, and does not extend further. (10) Wherefore we
form as many simple ideas as we please, without any fear of error.

[73] (1) It only remains for us to inquire by what power our mind
can form true ideas, and how far such power extends. (2) It is
certain that such power cannot extend itself infinitely. (3) For
when we affirm somewhat of a thing, which is not contained in the
concept we have formed of that thing, such an affirmation shows a
defect of our perception, or that we have formed fragmentary or
mutilated ideas. (4) Thus we have seen that the notion of a
semicircle is false when it is isolated in the mind, but true when
it is associated with the concept of a sphere, or of some cause
determining such a motion. (73:5) But if it be the nature of a