This lucid and important book was considered by Schopenhauer as the introduction to his magnum opus "The World as Will and as Representation". It can be conceived as Schopenhauer's alternative version to Kant's "Critique of Pure Reason" as an attempt to map all A-PRIORI knowledge. Schopenhauer, an obvious sequel to Kant, differentiates himself from Kant in this book in two basic assumptions: 1. There is no distinction between REPRESENTATION and OBJECT. We perceive objects directly, not through a subjective "buffer". 2. PERCEPTION is not logically independent of UNDERSTANDING, on the contrary. We perceive objects (necessarily) already understood, i.e. determined and related to other objects. Schopenhauer interprets the last premiss as the Principle of Sufficient Reason, which he claims to be the root of all A-PRIORI knowledge.