he mind,
therefore, will think as before, that is to say, it will again
contemplate the external body as present. This will happen as often as
the fluid parts of the human body strike against those planes by their
own spontaneous motion. Therefore, although the external bodies by which
the human body was once affected do not exist the mind will perceive
them as if they were present so often as this action is repeated in the
body.

We see, therefore, how it is possible for us to contemplate things which
do not exist as if they were actually present. This may indeed be
produced by other causes, but I am satisfied with having here shown one
cause through which I could explain it, just as if I had explained it
through the true cause. I do not think, however, that I am far from the
truth, since no postulate which I have assumed contains anything which
is not confirmed by an experience that we cannot mistrust, after we have
proved the existence of the human body as we perceive it.

We clearly see, moreover, what is the difference between the idea, for
example, of Peter, which constitutes the essence of the mind itself of
Peter, and the idea of Peter himself which is in another man; for
example, in Paul. For the former directly manifests the essence of the
body of Peter himself, nor does it involve existence unless so long as
Peter exists; the latter, on the other hand, indicates rather the
constitution of the body of Paul than the nature of Peter; and therefore
so long as Paul's body exists with that constitution, so long will
Paul's mind contemplate Peter as present, although he does not exist.
But in order that we may retain the customary phraseology, we will give
to those modifications of the human body, the ideas of which represent
to us external bodies as if they were present, the name of _images of
things_, although they do not actually reproduce the forms of the
things. When the mind contemplates bodies in this way, we will say that
it imagines. Here I wish it to be observed, in order that I may begin to
show what _error_ is, that these imaginations of the mind, regarded by
themselves, contain no error, and that the mind is not in error because
it imagines, but only in so far as it is considered as wanting in an
idea which excludes the existence of those things which it imagines as
present. For if the mind, when it imagines non-existent things to be
present, could at the same time know that those things did not really