Transcription of LocHum,588[3]et589[1]
— 588 —
What is requisite for our Knowledge of Substances.
      §14. Before we can have any tolerable knowledge of this kind, we
— 589 —
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 modifica-
tions 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, that so 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 Opera-
tions of Spirits, both their thinking and moving of Bodies, we at first
sight find our selves 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.
Locke Hum IV, 6, §14, pp. 588-589