— 140 —
Three sorts of Qualities in Bodies.       §23. The Qualities then that are in Bodies rightly considered, are
of Three sorts.
      First, The Bulk, Figure, Number, Situation, and Motion, or Rest of
their solid Parts; those are in them, whether we perceive them or
no; and when they are of that size, that we can discover them, we
have by these an Idea of the thing, as it is in it self, as is plain in
artificial things. These I call primary Qualities.
      Secondly, The Power that is in any Body, by Reason of its insensible
primary Qualities, to operate after a peculiar manner on any of our
Senses, and thereby produce in us the different Ideas of several Colours,
Sounds, Smells, Tasts, etc. These are usually called sensible
      Thirdly, The Power that is in any Body, by Reason of the particular
Constitution of its primary Qualities, to make such a change in the
Bulk, Figure, Texture, and Motion of another Body, as to make it
operate on our Senses, differently from what it did before. Thus the
— 141 —
Sun has a Power to make Wax white, and Fire to make Lead fluid.
These are usually called Powers.
      The First of these, as has been said, I think, may be properly
called real Original, or primary Qualities, because they are in the
things themselves, whether they are perceived or no: and upon their
different Modifications it is, that the secondary Qualities depend.
      The other two, are only Powers to act differently upon other
things, which Powers result from the different Modifications of
those primary Qualities.
Locke Hum II, 8, §23, pp. 140-141