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Chapter III

Of Ideas of one Sense.
Division of simple Ideas.       §1. The better to conceive the Ideas, we receive from Sensation, it
may not be amiss for us to consider them, in reference to the
different ways, whereby they make their Approaches to our minds,
and make themselves perceivable by us.
      First then, There are some, which come into our minds by one
Sense only.
      Secondly, There are others, that convey themselves into the mind
by more Senses than one.
      Thirdly, Others that are had from Reflection only.
      Fourthly, There are some that make themselves way, and are
suggested to the mind by all the ways of Sensation and Reflection.
We shall consider them apart under these several Heads.
Ideas of one Sense.       First, There are some Ideas, which have admittance only through one
Sense, which is peculiarly adapted to receive them. Thus Light and
Colours, as white, red, yellow, blue; with their several Degrees or
Shades, and Mixtures, as Green, Scarlet, Purple, Sea-green, and the
rest, come in only by the Eyes: All kinds of Noises, Sounds, and
Tones only by the Ears: The several Tastes and Smells, by the Nose
and Palate. And if these Organs, or the Nerves which are the
Conduits, to convey them from without to their Audience in the
Brain, the mind’s Presence-room (as I may so call it) are any of
them so disordered, as not to perform their Functions, they have no
Postern to be admitted by; no other way to bring themselves into
view, and be perceived by the Understanding.
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The most considerable of those, belonging to the Touch, are
Heat and Cold, and Solidity; all the rest, consisting almost wholly
in the sensible Configuration, as smooth and rough; or else more,
or less firm adhesion of the Parts, as hard and soft, tough and
brittle, are obvious enough.
Locke Hum II, 3, §1, pp. 121-122