All supreme principles of morality, that are genuine, must rest on pure Reason solely; and the mistake of the popular practical philosophies in vogue, one and all--whether advancing as their principle a special determination of human nature, or Perfection, or Happiness, or Moral Feeling, or Fear of God, or a little of this and a little of that--is that there has been no previous consideration whether the principles of morality are to be sought for in our empirical knowledge of human nature at all. Such consideration would have shown them to be altogether _à priori_, and would have appeared as a _pure_ practical philosophy or metaphysic of morals (upon the completion of which any popularizing might have waited), kept free from admixture of Anthropology, Theology, Physics, Hyperphysics, &c., and setting forth the conception of Duty as purely rational, without the confusion of empirical motives. To a metaphysic of this kind, Kant is now to ascend from the popular philosophy, with its stock-in-trade of single instances, following out the practical faculty of Reason from the general rules determining it, to the point where the conception of Duty emerges. While things in nature work according to laws, rational beings alone can act according to a conceived idea of laws, _i.e._, to principles. This is to have a Will, or, what is the same, Practical Reason, reason being required in deducing actions from laws. If the Will follows Reason exactly and without fail, actions objectively necessary are necessary also subjectively; if, through subjective conditions (inclinations, &c.), the Will does not follow Reason inevitably, objectively necessary actions become subjectively contingent, and towards the objective laws the attitude of the will is no longer unfailing choice, but _constraint_. A constraining objective principle mentally represented, is a _command_; its formula is called _Imperative_, for which the expression is _Ought_. A will perfectly good--_i.e._, subjectively determined to follow the objective laws of good as soon as conceived--knows no Ought. Imperatives are only for an imperfect, such as is the human, will. _Hypothetical_ Imperatives represent the practical necessity of an action as a means to an end, being _problematical_ or _assertory_ principles, according as the end is possible or real. _Categorical_ Imperatives represent an action as objectively necessary for itself, and count as _apodeictical_ principles.