“Some logicians, indeed, affirm that logic presupposes _psychological_ principles. But it is just as inappropriate to bring principles of this kind into logic as to derive the science of morals from life. If we were to take the principles from psychology, that is, from observations on our understanding, we should merely see _how_ thought takes place, and _how_ it is affected by the manifold subjective hindrances and conditions; so that this would lead only to the knowledge of _contingent_ laws. But in logic the question is not of _contingent_, but of _necessary_ laws; not how we do think, but how we ought to think. The rules of logic, then, must not be derived from the _contingent_, but from the _necessary_ use of the understanding which without any psychology a man finds in himself. In logic we do not want to know how the understanding is and thinks, and how it has hitherto proceeded in thinking, but how it ought to proceed in thinking. Its business is to teach us the correct use of reason, that is, the use which is consistent with itself.”[651] By a canon Kant means a system of _a priori_ principles for the correct employment of a certain faculty of knowledge.[652] By an organon Kant means instruction as to how knowledge may be extended, how new knowledge may be acquired. A canon formulates positive principles through the application of which a faculty can be directed and disciplined. A canon is therefore a discipline based on positive principles of correct use. The term discipline is, however, reserved by Kant[653] to signify a purely negative teaching, which seeks only to prevent error and to check the tendency to deviate from rules. When a faculty has no correct use (as, for instance, pure speculative reason), it is subject only to a discipline, not to a canon. A discipline is thus “a separate, negative code,” “a system of caution and self-examination.” It is further distinguished from a canon by its taking account of other than purely _a priori_ conditions. It is related to a pure canon much as applied is related to general logic. As a canon supplies principles for the _directing_ of a faculty, its distinction from an organon obviously cannot be made hard and fast. But here as elsewhere Kant, though rigorous and almost pedantic in the drawing of distinctions, is correspondingly careless in their application. He describes special logic as the organon of this or that science.[654] We should expect from the definition given in the preceding sentence that it would rather be viewed as a canon. In A 46 = B 63 Kant speaks of the _Aesthetic_ as an organon.