— 286 —
      §73. And thus I have, in a short draught, given a view of our
original Ideas, from whence all the rest are derived, and of which
they are made up; which if I would consider, as a Philosopher, and
examine on what Causes they depend, and of what they are made,
I believe they all might be reduced to these very few primary, and
original ones, viz.

Extension,
Solidity,
Mobility, or the Power of being moved;

which by our Senses we receive from Body:

Perceptivity, or the Power of perception, or thinking;
Motivity, or the Power of moving;

which by reflection we receive from our Minds. I crave leave to
— 287 —
make use of these two new Words, to avoid the danger of being
mistaken in the use of those which are aequivocal. To which if we
add

Existence,
Duration,
Number;

which belong both to the one, and the other, we have, perhaps, all
the Original Ideas on which the rest depend. For by these, I imagine,
might be explained the nature of Colours, Sounds, Tastes, Smells,
and all other Ideas we have, if we had but Faculties acute enough to
perceive the severally modified Extensions, and Motions, of these
minute Bodies, which produce those several Sensations in us. But
my present purpose being only to enquire into the Knowledge the
Mind has of Things, by those Ideas, and Appearances, which God has
fitted it to receive from them, and how the Mind comes by that
Knowledge; rather than into their Causes, or manner of Production,
I shall not, contrary to the Design of this Essay, set my self to
enquire philosophically into the peculiar Constitution of Bodies,
and the Configuration of Parts, whereby they have the power to
produce in us the Ideas of their sensible Qualities: I shall not enter
any farther into that Disquisition; it sufficing to my purpose to
observe, That Gold, or Saffron, has a power to produce in us the
Idea of Yellow; and Snow, or Milk, the Idea of White; which we can
only have by our Sight, without examining the Texture of the
Parts of those Bodies, or the particular Figures, or Motion of the
Particles, which rebound from them, to cause in us that particular
Sensation: though when we go beyond the bare Ideas in our Minds,
and would enquire into their Causes, we cannot conceive any thing
else, to be in any sensible Object, whereby it produces different
Ideas in us, but the different Bulk, Figure, Number, Texture, and
Motion of its insensible Parts.
Locke Hum II, 21, §73, pp. 286-287