10. As far as any such co-existence can be known, so far universal
propositions may be certain. But this will go but a little way. The
more, indeed, of these coexisting qualities we unite into one
complex idea, under one name, the more precise and determinate we make
the signification of that word; but never yet make it thereby more
capable of universal certainty, in respect of other qualities not
contained in our complex idea: since we perceive not their connexion
or dependence on one another; being ignorant both of that real
constitution in which they are all founded, and also how they flow
from it. For the chief part of our knowledge concerning substances
is not, as in other things, barely of the relation of two ideas that
may exist separately; but is of the necessary connexion and
co-existence of several distinct ideas in the same subject, or of
their repugnancy so to co-exist. Could we begin at the other end,
and discover what it was wherein that colour consisted, what made a
body lighter or heavier, what texture of parts made it malleable,
fusible, and fixed, and fit to be dissolved in this sort of liquor,
and not in another;- if, I say, we had such an idea as this of bodies,
and could perceive wherein all sensible qualities originally
consist, and how they are produced; we might frame such abstract ideas
of them as would furnish us with matter of more general knowledge, and
enable us to make universal propositions, that should carry general
truth and certainty with them.
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