3. We may have the ideas when we are ignorant of their physical
causes. A painter or dyer who never inquired into their causes hath
the ideas of white and black, and other colours, as clearly,
perfectly, and distinctly in his understanding, and perhaps more
distinctly, than the philosopher who hath busied himself in
considering their natures, and thinks he knows how far either of
them is, in its cause, positive or privative; and the idea of black is
no less positive in his mind than that of white, however the cause
of that colour in the external object may be only a privation.
4. Why a privative cause in nature may occasion a positive idea.
If it were the design of my present undertaking to inquire into the
natural causes and manner of perception, I should offer this as a
reason why a privative cause might, in some cases at least, produce
a positive idea; viz. that all sensation being produced in us only
by different degrees and modes of motion in our animal spirits,
variously agitated by external objects, the abatement of any former
motion must as necessarily produce a new sensation as the variation or
increase of it; and so introduce a new idea, which depends only on a
different motion of the animal spirits in that organ.
5. Negative names need not be meaningless. But whether this be so or
not I will not here determine, but appeal to every one's own
experience, whether the shadow of a man, though it consists of nothing
but the absence of light (and the more the absence of light is, the
more discernible is the shadow) does not, when a man looks on it,
cause as clear and positive idea in his mind as a man himself,
though covered over with clear sunshine? And the picture of a shadow
is a positive thing.
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