— 545 —
      §13. That the size, figure, and motion of one Body should cause
a change in the size, figure, and motion of another Body, is not
beyond our Conception; the separation of the Parts of one Body,
upon the intrusion of another; and the change from rest to motion,
upon impulse; these, and the like, seem to us to have some connexion
one with another. And if we knew these primary Qualities of Bodies,
we might have reason to hope, we might be able to know a great
deal more of these Operations of them one upon another: But our
Minds not being able to discover any connexion betwixt these pri-
mary qualities of Bodies, and the sensations that are produced in us
by them, we can never be able to establish certain and undoubted
Rules, of the Consequence or Co-existence of any secondary Qualities,
though we could discover the size, figure, or motion of those
invisible Parts, which immediately produce them. We are so far
from knowing what figure, size, or motion of parts produce a yellow
Colour, a sweet Taste, or a sharp Sound, that we can by no means
conceive how any size, figure, or motion of any Particles, can possibly
produce in us the Idea of any Colour, Taste, or Sound whatsoever;
there is no conceivable
Locke Hum IV, 3, §13, p. 545