— 633 —
Thirdly, Pleasure or Pain, which accompanies actual Sensation, accompanies not the returning of those Ideas without the external Objects.
      §6. Thirdly, Add to this, that many of those Ideas are produced in us
with pain, which afterwards we remember without the least offence. Thus
the pain of Heat or Cold, when the Idea of it is revived in our
Minds, gives us no disturbance; which, when felt, was very
troublesome, and is again, when actually repeated: which is oc-
casioned by the disorder the external Object causes in our Bodies,
when applied to it: And we remember the pain of Hunger, Thirst, or
the Head-ach, without any pain at all; which would either never dis-
turb us, or else constantly do it, as often as we thought of it, were
there nothing more but Ideas floating in our Minds, and appearances
entertaining our Fancies, without the real Existence of Things
affecting us from abroad. The same may be said of Pleasure,
accompanying several actual Sensations: And though mathematical
demonstrations depend not upon sense, yet the examining them by
Diagrams, gives great credit to the Evidence of our Sight, and seems
to give it a Certainty approaching to that of the Demonstration it
self. For it would be very strange, that a Man should allow it for an
undeniable Truth, that two Angles of a Figure, which he measures
by Lines and Angles of a Diagram, should be bigger one than the
other; and yet doubt of the Existence of those Lines and Angles,
which by looking on, he makes use of to measure that by.
Locke Hum IV, 11, §6, p. 633