ons,
can ever lead to any solid and rational system. They are the coherence
and constancy of our perceptions, which produce the opinion of their
continued existence; though these qualities of perceptions have no
perceivable connexion with such an existence. The constancy of our
perceptions has the most considerable effect, and yet is attended with
the greatest difficulties. It is a gross illusion to suppose, that
our resembling perceptions are numerically the same; and it is this
illusion, which leads us into the opinion, that these perceptions are
uninterrupted, and are still existent, even when they are not present
to the senses. This is the case with our popular system. And as to
our philosophical one, it is liable to the same difficulties; and is
over-and-above loaded with this absurdity, that it at once denies and
establishes the vulgar supposition. Philosophers deny our resembling
perceptions to be identically the same, and uninterrupted; and yet have
so great a propensity to believe them such, that they arbitrarily invent
a new set of perceptions, to which they attribute these qualities. I
say, a new set of perceptions: For we may well suppose in general, but
it is impossible for us distinctly to conceive, objects to be in their
nature any thing but exactly the same with perceptions. What then can
we look for from this confusion of groundless and extraordinary opinions
but error and falshood? And how can we justify to ourselves any belief
we repose in them?

This sceptical doubt, both with respect to reason and the senses, is
a malady, which can never be radically cured, but must return upon
us every moment, however we may chace it away, and sometimes may seem
entirely free from it. It is impossible upon any system to defend either
our understanding or senses; and we but expose them farther when we
endeavour to justify them in that manner. As the sceptical doubt arises
naturally from a profound and intense reflection on those subjects,
it always encreases, the farther we carry our reflections, whether in
opposition or conformity to it. Carelessness and in-attention alone can
afford us any remedy. For this reason I rely entirely upon them; and
take it for granted, whatever may be the reader's opinion at this
present moment, that an hour hence he will be persuaded there is both an
external and internal world; and going upon that supposition, I intend
to examine some general systems both ancient and modern, which ha