From Twilight of the Idols:
2 With the highest respect, I except the name of Heraclitus. When the rest of the philosophic folk rejected the testimony of the senses because they showed multiplicity and change, he rejected their testimony because they showed things as if they had permanence and unity. Heraclitus too did the senses an injustice. They lie neither in the way the Eleatics believed, nor as he believed--they do not lie at all. What we make of their testimony, that alone introduces lies; for example, the lie of unity, the lie of thinghood, of substance, of permanence. "Reason" is the cause of our falsification of the testimony of the senses. Insofar as the senses show becoming, passing away, and change, they do not lie. But Heraclitus will remain eternally right with his assertion that being is an empty fiction. The "apparent" world is the only one: the "true" world is merely added by a lie.
3 And what magnificent instruments of observation we possess in our senses! This nose, for example, of which no philosopher has yet spoken with reverence and gratitude, is actually the most delicate instrument so far at our disposal: it is able to detect minimal differences of motion which even a spectroscope cannot detect. Today we possess science precisely to the extent to which we have decided to accept the testimony of the senses--to the extent to which we sharpen them further, arm them, and have learned to think them through. The rest is miscarriage and not-yet-science--in other words, metaphysics, theology, psychology, epistemology--or formal science, a doctrine of signs, such as logic and that applied logic which is called mathematics. In them reality is not encountered at all, not even as a problem--no more than the question of the value of such a sign-convention as logic.