Reason continually seeks to establish newer and newer principles. The newer principles become more and more removed from experience. This progression would lead reason to continue questioning experience indefinitely. "Thus it [reason] finds itself compelled to resort to principles that go beyond all possible use in experience, and that nonetheless seem so little suspect that even common human reason agrees with them" (634). This is where the real problem surfaces. Many conflicts and contradictions are found on the level of principles which experience cannot test. The presence of the contradictions implies that reason must have made some mistakes along its upward path from experience to metaphysics. These mistakes remain hidden, however, and reason does not seem able to find them.
Kant uses this situation as an opportunity to define metaphysics. Metaphysics is the field which deals with issues beyond the scope of experience. Metaphysics is a battlefield of ideas. True metaphysical principles will have to be able to resolve conflicts that experience is unable to. Because metaphysics is a natural end of human reason, it is inevitably tied to the human condition. Humanity has a vested interest in establishing some true metaphysical principles. This task appears rather daunting. Reason constantly fails to achieve answers beyond any controversy in the arena of metaphysics.
Next, Kant explains the meaning of the title of his essay. Kant realizes that reason is the only faculty we have that could possibly be of use in establishing metaphysical principles. None of our physical or emotional faculties have the ability to combat reason on the metaphysical level. Kant says that we must turn reason against itself. This act of self-cognition, says Kant, is the most difficult of all reason's tasks. Using only its principles, reason must check itself. Reason must "set up a tribunal that will make reason secure in its rightful claims and will dismiss all baseless pretensions not by fiat, but in accordance with reason's eternal and immutable laws.
