stand, whenever they have any distinct
and determinate signification, have a discoverable connexion or
inconsistency with but a very few other ideas, the certainty of
universal propositions concerning substances is very narrow and scanty,
in that part which is our principal inquiry concerning them; and there
are scarce any of the names of substances, let the idea it is applied
to be what it will, of which we can generally, and with certainty,
pronounce, that it has or has not this or that other quality belonging
to it, and constantly co-existing or inconsistent with that idea,
wherever it is to be found.

14. What is requisite for our Knowledge of Substances.

Before we can have any tolerable knowledge of this kind, we must First
know what changes the primary qualities of one body do regularly produce
in the primary qualities of another, and how. Secondly, We must know
what primary qualities of any body produce certain sensations or ideas
in us. This is in truth no less than to know ALL the effects of matter,
under its divers modifications of bulk, figure, cohesion of parts,
motion and rest. Which, I think every body will allow, is utterly
impossible to be known by us without revelation. Nor if it were revealed
to us what sort of figure, bulk, and motion of corpuscles would produce
in us the sensation of a yellow colour, and what sort of figure, bulk,
and texture of parts in the superficies of any body were fit to give
such corpuscles their due motion to produce that colour; would that be
enough to make universal propositions with certainty, concerning the
several sorts of them; unless we had faculties acute enough to perceive
the precise bulk, figure, texture, and motion of bodies, in those minute
parts, by which they operate on our senses, so that we might by those
frame our abstract ideas of them. I have mentioned here only
corporeal substances, whose operations seem to lie more level to our
understandings. For as to the operations of spirits, both their thinking
and moving of bodies, we at first sight find ourselves at a loss; though
perhaps, when we have applied our thoughts a little nearer to the
consideration of bodies and their operations, and examined how far our
notions, even in these, reach with any clearness beyond sensible matter
of fact, we shall be bound to confess that, even in these too, our
discoveries amount to very little beyond perfect ignorance and
incapacity.

15. Whilst our complex Ideas