The author critiques sensism and Condillac's claim that all mental activity reduces to transformed sensation, arguing for distinct intellectual acts and the existence of pure ideas and intellectual intuition. He distinguishes geometrical and non-geometrical ideas, examines the role of sensible intuition versus discursive cognition, and compares Aristotelian and Kantian accounts of the intellect. Subsequent sections develop the idea of being—its simplicity, negation, identity, distinction between essence and existence—and explore the origins of unity and number, the necessity in ideas, and the relation between language and general concepts, defending the reality and explanatory power of universal reason.