Such a metaphysic of morals, completely isolated, not mixed with any anthropology, theology, physics, or hyperphysics, and still less with occult qualities (which we might call hypophysical), is not only an indispensable substratum of all sound theoretical knowledge of duties, but is at the same time a desideratum of the highest importance to the actual fulfilment of their precepts.  For the pure conception of duty, unmixed with any foreign addition of empirical attractions, and, in a word, the conception of the moral law, exercises on the human heart, by way of reason alone (which first becomes aware with this that it can of itself be practical), an influence so much more powerful than all other springs [Footnote:  I have a letter from the late excellent Sulzer, in which he asks me what can be the reason that moral instruction, although containing much that is convincing for the reason, yet accomplishes so little?  My answer was postponed in order that I might make it complete.  But it is simply this, that the teachers themselves have not got their own notions clear, and when they endeavour to make up for this by raking up motives of moral goodness from every quarter, trying to make their physic right strong, they spoil it.  For the commonest understanding shows that if we imagine, on the one hand, an act of honesty done with steadfast mind, apart from every view to advantage of any kind in this world or another, and even under the greatest temptations of necessity or allurement, and, on the other hand, a similar act which was affected, in however low a degree, by a foreign motive, the former leaves far behind and eclipses the second; it elevates the soul, and inspires the wish to be able to act in like manner oneself.  Even moderately young children feel this impression, and one should never represent duties to them in any other light.] which may be derived from the field of experience, that in the consciousness of its worth, despises the latter, and can by degrees become their master; whereas a mixed ethics, compounded partly of motives drawn from feelings and inclinations, and partly also of conceptions of reason, must make the mind waver between motives which cannot be brought under any principle, which lead to good only by mere accident, and very often also to evil.

From what has been said, it is clear that all moral conceptions have their seat and origin completely a priori in the reason, and that, moreover, in the commonest reason just as truly as in that which is in the highest degree speculative; that they cannot be obtained by abstraction from any empirical, and therefore merely contingent knowledge; that it is just this purity of their origin that makes them worthy to serve as our supreme practical principle, and that just in proportion as we add anything empirical, we detract from their genuine influence, and from the absolute value of actions; that it is not only of the greatest necessity, in a purely speculative point