Proofs of transcendental propositions about pure reason (God, soul, free will, causality, simplicity) must first prove whether the concept is valid. Reason should be moderated and not asked to perform beyond its power. The three rules of the proofs of pure reason are: (1) consider the legitimacy of your principles, (2) each proposition can have only one proof because it is based on one concept and its general object, and (3) only direct proofs can be used, never indirect proofs (e.g., a proposition is true because its opposite is false). By attempting to directly prove transcendental assertions, it will become clear that pure reason can gain no speculative knowledge and must restrict itself to practical, moral principles. The dogmatic use of reason is called into question by the skeptical use of reason but skepticism does not present a permanent state for human reason. Kant proposes instead a critique of pure reason by means of which the limitations of reason are clearly established and the field of knowledge is circumscribed by experience. According to the rationalists and skeptics, there are analytic judgments "a priori" and synthetic judgments "a posteriori". Analytic judgments "a posteriori" do not really exist. Added to all these rational judgments is Kant's great discovery of the synthetic judgment "a priori".