within the province of method, it belongs rather to inquiries
concerning obstinacy and its cure.

[78] (1) Real doubt is never produced in the mind by the thing
doubted of. (2) In other words, if there were only one idea in
the mind, whether that idea were true or false, there would be no
doubt or certainty present, only a certain sensation. (3) For an
idea is in itself nothing else than a certain sensation. (4) But
doubt will arise through another idea, not clear and distinct
enough for us to be able to draw any certain conclusions with
regard to the matter under consideration; that is, the idea which
causes us to doubt is not clear and distinct. (5) To take an example.
(78:6) Supposing that a man has never reflected, taught by experience
or by any other means, that our senses sometimes deceive us, he will
never doubt whether the sun be greater or less than it appears.
(7) Thus rustics are generally astonished when they hear that the
sun is much larger than the earth. (8) But from reflection on the
deceitfulness of the senses [78a] doubt arises, and if, after
doubting, we acquire a true knowledge of the senses, and how things
at a distance are represented through their instrumentality, doubt
is again removed.

[79] (1) Hence we cannot cast doubt on true ideas by the supposition
that there is a deceitful Deity, who leads us astray even in what is
most certain. (2) We can only hold such an hypothesis so long as we
have no clear and distinct idea - in other words, until we reflect
the knowledge which we have of the first principle of all things, and
find that which teaches us that God is not a deceiver, and until we
know this with the same certainty as we know from reflecting on the
are equal to two right angles. (3) But if we have a knowledge of God