sense--the one intelligible or in the mind, the other real and without
the mind; whereby unthinking things are thought to have a natural
subsistence of their own distinct from being perceived by spirits. This,
which, if I mistake not, has been shown to be a most groundless and
absurd notion, is the very root of Scepticism; for, so long as men
thought that real things subsisted without the mind, and that their
knowledge was only so far forth real as it was conformable to real
things, it follows they could not be certain they had any real knowledge
at all. For how can it be known that the things which are perceived are
conformable to those which are not perceived, or exist without the mind?

87. Colour, figure, motion, extension, and the like, considered only as
so many sensations in the mind, are perfectly known, there being nothing
in them which is not perceived. But, if they are looked on as notes or
images, referred to things or archetypes existing without the mind, then
are we involved all in scepticism. We see only the appearances, and not
the real qualities of things. What may be the extension, figure, or
motion of anything really and absolutely, or in itself, it is impossible
for us to know, but only the proportion or relation they bear to our
senses. Things remaining the same, our ideas vary, and which of them, or
even whether any of them at all, represent the true quality really
existing in the thing, it is out of our reach to determine. So that, for
aught we know, all we see, hear, and feel may be only phantom and vain
chimera, and not at all agree with the real things existing in rerum
natura. All this scepticism follows from our supposing a difference
between things and ideas, and that the former have a subsistence without
the mind or unperceived. It were easy to dilate on this subject, and show
how the arguments urged by sceptics in all ages depend on the supposition
of external objects.