Because our sense organs are themselves part of physical reality, the message that they convey from reality is necessarily reliable and free of illusion. That message is rich but essentially uninterpreted, informing us that something is, that some fact of nature—which we must then identify—has occurred.

Furthermore, the very notion that the previous example constitutes an "optical illusion" derives from prior sensory data. Those who call this experience an "illusion" must have already inferred that the stick is in fact straight—and that inference ultimately depends upon previous sensory experiences. All such attempts to disprove the validity of the senses will be similarly found to rest on the implicit assumption that the senses do in fact convey valid knowledge—and for this reason we can treat the validity of the senses as axiomatic. (Regarding axioms, cf. p. 1.2:1 or the Glossary.) Such so-called "optical illusions" indicate, not that our senses can deceive us, but that we can deceive ourselves by failing to integrate fully the knowledge deriving from all of our sensory experiences.