25. Why the secondary are ordinarily taken for real qualities, and not for bare powers.
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 show 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 anything in the thing producing it; wherefore we look on it as a
bare effect of power. For, through receiving the idea of heat or light from the sun, we are apt to think it is 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 anything in the sun, because we
find not those different colours in the sun itself. 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.