— 142 —
      §25. The Reason, Why the one are ordinarily taken for real Qualities,
and the other only for bare Powers, seems to be, because the Ideas we
have of distinct Colours, Sounds, etc. containing nothing at all in
them, of Bulk, Figure, or Motion, we are not apt to think them the
Effects of these primary Qualities, which appear not to our Senses to
operate in their Production; and with which, they have not any
apparent Congruity, or conceivable Connexion. Hence it is, that
we are so forward to imagine, that those Ideas are the resemblances
of something really existing in the Objects themselves: Since
Sensation discovers nothing of Bulk, Figure, or Motion of parts in
their Production; nor can Reason shew, how Bodies by their Bulk,
Figure, and Motion, should produce in the Mind the Ideas of Blue,
or Yellow, etc. But in the other Case, in the Operations of Bodies,
changing the Qualities one of another, we plainly discover, that the
Quality produced, hath commonly no resemblance with any thing
in the thing producing it; wherefore we look on it as a bare Effect of
Power. For though receiving the Idea of Heat, or Light, from the
Sun, we are apt to think,’tis a Perception and Resemblance of such
a Quality in the Sun: yet when we see Wax, or a fair Face, receive
change of Colour from the Sun, we cannot imagine, that to be the
Reception or Resemblance of any thing in the Sun, because we
find not those different Colours in the Sun it self. For our Senses,
being able to observe a likeness, or unlikeness of sensible Qualities
in two different external Objects, we forwardly enough conclude
the Production of any sensible Quality in any Subject, to be an
Effect of bare Power, and not the Communication of any Quality,
which was really in the efficient, when we find no such sensible
Quality in the thing that produced it. But our Senses, not being
able to discover any unlikeness between the Idea produced in us,
and the Quality of the Object producing it, we are apt to imagine,
that our Ideas are resemblances of something in the Objects, and not
the Effects of certain Powers, placed in the Modification of their
primary Qualities, with which primary Qualities the Ideas produced
in us have no resemblance.
Locke Hum II, 8, §25, p. 142