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      §9. But this is not, I think, usual in any of our Ideas, but those
received by Sight : Because Sight, the most comprehensive of all our
Senses, conveying to our Minds the Ideas of Light and Colours,
which are peculiar only to that Sense; and also the far different
Ideas of Space, Figure, and Motion, the several varieties whereof
change the appearances of its proper Object, viz. Light and Colours,
we bring our selves by use, to judge of the one by the other. This in
many cases, by a settled habit, in things whereof we have frequent
experience, is performed so constantly, and so quick, that we take
that for the Perception of our Sensation, which is an Idea formed by
our Judgment; so that one, viz. that of Sensation, serves only to
excite the other, and is scarce taken notice of it self; as a Man who
— 147 —
reads or hears with attention and understanding, takes little notice
of the Characters, or Sounds, but of the Ideas, that are excited in
him by them.
Locke Hum II, 9, §9, pp. 146-147