Returning to the perception, it is regarded as due to an interaction between the object and the sense-organ, both of which, according to the doctrine of Heraclitus, are always changing, and both of which, in changing, change the percept. Socrates remarks that when he is well he finds wine sweet, but when ill, sour. Here it is a change in the percipient that causes the change in the percept.p. 150.

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