for ascertaining that true colour, and distinguishing it from
apparent ones.

     . I own myself entirely satisfied, that they are all
equally apparent, and that there is no such thing as colour
really inhering in external bodies, but that it is altogether in
the light. And what confirms me in this opinion is, that in
proportion to the light colours are still more or less vivid; and
if there be no light, then are there no colours perceived.
Besides, allowing there are colours on external objects, yet, how
is it possible for us to perceive them? For no external body
affects the mind, unless it acts first on our organs of sense.
But the only action of bodies is motion; and motion cannot be
communicated otherwise than by impulse. A distant object
therefore cannot act on the eye; nor consequently make itself or
its properties perceivable to the soul. Whence it plainly follows
that it is immediately some contiguous substance, which,
operating on the eye, occasions a perception of colours: and such
is light.

     . Howl is light then a substance?

     .. I tell you, Philonous, external light is nothing but
a thin fluid substance, whose minute particles being agitated
with a brisk motion, and in various manners reflected from the
different surfaces of outward objects to the eyes, communicate
different motions to the optic nerves; which, being propagated to
the brain, cause therein various impressions; and these are
attended with the sensations of red, blue, yellow, &c.

     . It seems then the light doth no more than shake the
optic nerves. {187}

     . Nothing else.

     . And consequent to each particular motion of the
nerves, the mind is affected with a sensation, which is some
particular colour.

     . Right.

     . And these sensations have no existence without the
mind.

     . They have not.

     . How then do you affirm that colours are in the
light; since by  you understand a corporeal substance
external to the mind?

     . Light and colours, as immediately perceived by us, I
grant cannot exist without the mind. But in themselves they are
only the motions and configurations of certain insensible
particles of matter.

     . Colours then, in the vulgar sense, or taken for the
immediate objects of sight, cannot agree to any but a perceiving
substance.

     . That is what I say.

     . Well then, since you give up the point as to those
sensible qualities which are alone thought colours by all mankind
beside, you may hold what you please with regard to those
invisible ones of the philosophers. It is not my business to
dispute about ; only I would advise you to bethink
yourself, whether, considering the inquiry we are upon, it be
prudent for you to affirm -- <the red and blue which we see are
not real colours>, <but certain unknown motions and figures which
no man ever did or can see are truly so>. Are not these shocking
notions, and are not they subject to as many ridiculous
inferences, as those you were obliged to renounce before in the
case of sounds?

     . I frankly own, Philonous, that it is in vain to
longer. Colours, sounds, tastes, in a word all those termed
<secondary qualities>, have certainly no existence without the
mind. But by this acknowledgment I must not be supposed to
derogate, the reality of Matter, or external objects; seeing it
is no more than several philosophers maintain, who nevertheless
are the farthest imaginable from denying Matter. For the clearer
understanding of this, you must know sensible qualities are by
philosophers divided into  and . The former
are Extension, Figure, Solidity, Gravity, Motion, and Rest; {188}
and these they hold exist really in bodies. The latter are those
above enumerated; or, briefly, <all sensible qualities beside the
Primary>; which they assert are only so many sensations or ideas
existing nowhere but in the mind. But all this, I doubt not, you
are apprised of. For my part, I have been a long time sensible
there was such an opinion current among philosophers, but was
never thoroughly convinced of its truth until now.

     . You are still then of opinion that  and
<figures are> inherent in external unthinking substances?

     . I am.

     . But what if the same arguments which are brought
against Secondary Qualities will hold good against these also?