"It is evident to any one who takes a survey
of the objects of human knowledge,
that they are either ideas actually imprinted on the senses;
or else such as are perceived by attending
to the passions and operations of the mind;
or lastly, ideas formed by help of memory and imagination
--either compounding, dividing,
or barely representing those originally perceived in the aforesaid ways.
By sight I have the ideas of light and colours,
with their several degrees and variations.
By touch I perceive hard and soft, heat and cold, motion and resistance,
and of all these more and less either as to quantity or degree.
Smelling furnishes me with odours; the palate with tastes;
and hearing conveys sounds to the mind
in all their variety of tone and composition.
And as several of these are observed to accompany each other,
they come to be marked by one name, and so to be reputed as one thing.
Thus, for example a certain colour, taste, smell, figure and consistence
having been observed to go together, are accounted one distinct thing,
signified by the name apple".
A Treatise Concerning the Principles of Human Knowledge.