The cause of these mistakes is no other than the following:  Those who are accustomed only to physiological explanations will not admit into their heads the categorical imperative from which these laws dictatorially proceed, notwithstanding that they feel themselves irresistibly forced by it.  Dissatisfied at not being able to explain what lies wholly beyond that sphere, namely, freedom of the elective will, elevating as is this privilege, that man has of being capable of such an idea.  They are stirred up by the proud claims of speculative reason, which feels its power so strongly in the fields, just as if they were allies leagued in defence of the omnipotence of theoretical reason and roused by a general call to arms to resist that idea; and thus they are at present, and perhaps for a long time to come, though ultimately in vain, to attack the moral concept of freedom and if possible render it doubtful.

INTRODUCTION

INTRODUCTION TO THE METAPHYSICAL ELEMENTS OF ETHICS

Ethics in ancient times signified moral philosophy (philosophia moral is) generally, which was also called the doctrine of duties.  Subsequently it was found advisable to confine this name to a part of moral philosophy, namely, to the doctrine of duties which are not subject to external laws (for which in German the name Tugendlehre was found suitable).  Thus the system of general deontology is divided into that of jurisprudence (jurisprudentia), which is capable of external laws, and of ethics, which is not thus capable, and we may let this division stand.

I. Exposition of the Conception of Ethics

The notion of duty is in itself already the notion of a constraint of the free elective will by the law; whether this constraint be an external one or be self-constraint.  The moral imperative, by its categorical (the unconditional ought) announces this constraint, which therefore does not apply to all rational beings (for there may also be holy beings), but applies to men as rational physical beings who are unholy enough to be seduced by pleasure to the transgression of the moral law, although they themselves recognize its authority; and when they do obey it, to obey it unwillingly (with resistance of their inclination); and it is in this that the constraint properly consists. * Now, as man is a free (moral) being, the notion of duty can contain only self-constraint (by the idea of the law itself), when we look to the internal determination of the will (the spring), for thus only is it possible to combine that constraint (even if it were external) with the freedom of the elective will.  The notion of duty then must be an ethical one.

{Introduction ^paragraph 5}