Discourses, "What the Beginning of Philosophy is" (§1)

“Observe, this is the beginning of philosophy, a perception of the disagreement of men with one another, and an inquiry into the cause of the disagreement, and a condemnation and distrust of that which only “seems,” and a certain investigation of that which “seems” whether it “seems” rightly, and a discovery of some rule, as we have discovered a balance in the determination of weights, and a carpenter’s rule (or square) in the case of straight and crooked things.”