re made up
of nothing but an imperfect collection of those apparent qualities our
senses can discover, there can be few general propositions concerning
substances of whose real truth we can be certainly assured; since there
are but few simple ideas of whose connexion and necessary co-existence
we can have certain and undoubted knowledge. I imagine, amongst all the
secondary qualities of substances, and the powers relating to them,
there cannot any two be named, whose necessary co-existence, or
repugnance to co-exist, can certainly be known; unless in those of the
same sense, which necessarily exclude one another, as I have elsewhere
showed. No one, I think, by the colour that is in any body, can
certainly know what smell, taste, sound, or tangible qualities it has,
nor what alterations it is capable to make or receive on or from other
bodies. The same may be said of the sound or taste, &c. Our specific
names of substances standing for any collections of such ideas, it
is not to be wondered that we can with them make very few general
propositions of undoubted real certainty. But yet so far as any complex
idea of any sort of substances contains in it any simple idea, whose
NECESSARY co-existence with any other MAY be discovered, so far
universal propositions may with certainty be made concerning it: v.g.
could any one discover a necessary connexion between malleableness and
the colour or weight of gold, or any other part of the complex idea
signified by that name, he might make a certain universal proposition
concerning gold in this respect; and the real truth of this proposition,
that ALL GOLD IS MALLIABLE, would be as certain as of this, THE THREE
ANGLES OF ALL RIGHT-LINED TRIANGLES ARE ALL EQUAL TO TWO RIGHT ONES.

11. The Qualities which make our complex Ideas of Substances depend
mostly on external, remote, and unperceived Causes.

Had we such ideas of substances as to know what real constitutions
produce those sensible qualities we find in them, and how those
qualities flowed from thence, we could, by the specific ideas of
their real essences in our own minds, more certainly find out their
properties, and discover what qualities they had or had not, than we can
now by our senses: and to know the properties of gold, it would be
no more necessary that gold should exist, and that we should make
experiments upon it, than it is necessary for the knowing the properties
of a triangle, that a triangle should exist in any