The Critique of Practical Reason

by Immanuel Kant

* A reviewer who wanted to find some fault with this work
has hit the truth better, perhaps, than he thought, when he
says that no new principle of morality is set forth in it,
but only a new formula. But who would think of introducing a
new principle of all morality and making himself as it were
the first discoverer of it, just as if all the world before
him were ignorant what duty was or had been in thorough-
going error? But whoever knows of what importance to a
mathematician a formula is, which defines accurately what is
to be done to work a problem, will not think that a formula
is insignificant and useless which does the same for all
duty in general.

In the second part of the Analytic I have given, as I trust, a sufficient answer to the objection of a truth-loving and acute critic * of the Fundamental Principles of the Metaphysic of Morals- a critic always worthy of respect- the objection, namely, that the notion of good was not established before the moral principle, as he thinks it ought to have been. ** I have also had regard to many of the objections which have reached me from men who show that they have at heart the discovery of the truth, and I shall continue to do so (for those who have only their old system before their eyes, and who have already settled what is to be approved or disapproved, do not desire any explanation which might stand in the way of their own private opinion.)

PREFACE ^paragraph 20

* [See Kant's "Das mag in der Theoric ricktig seyn," etc.
Werke, vol. vii, p. 182.]
** It might also have been objected to me that I have not
first defined the notion of the faculty of desire, or of the
feeling of Pleasure, although this reproach would be unfair,
because this definition might reasonably be presupposed as
given in psychology. However, the definition there given
might be such as to found the determination of the faculty
of desire on the feeling of pleasure (as is commonly done),
and thus the supreme principle of practical philosophy would
be necessarily made empirical, which, however, remains to be
proved and in this critique is altogether refuted. It will,
therefore, give this definition here in such a manner as it
ought to be given, in order to leave this contested point
open at the beginning, as it should be. LIFE is the faculty
a being has of acting according to laws of the faculty of
desire. The faculty of DESIRE is the being's faculty of
becoming by means of its ideas the cause of the actual
existence of the objects of these ideas. PLEASURE is the
idea of the agreement of the object, or the action with the
subjective conditions of life, i.e., with the faculty of
causality of an idea in respect of the actuality of its
object (or with the determination of the forces of the
subject to action which produces it). I have no further need
for the purposes of this critique of notions borrowed from
psychology; the critique itself supplies the rest. It is
easily seen that the question whether the faculty of desire
is always based on pleasure, or whether under certain
conditions pleasure only follows the determination of
desire, is by this definition left undecided, for it is
composed only of terms belonging to the pure understanding,
i.e., of categories which contain nothing empirical. Such
precaution is very desirable in all philosophy and yet is
often neglected; namely, not to prejudge questions by
adventuring definitions before the notion has been
completely analysed, which is often very late. It may be
observed through the whole course of the critical philosophy
(of the theoretical as well as the practical reason) that
frequent opportunity offers of supplying defects in the old
dogmatic method of philosophy, and of correcting errors
which are not observed until we make such rational use of
these notions viewing them as a whole.

When we have to study a particular faculty of the human mind in its sources, its content, and its limits; then from the nature of human knowledge we must begin with its parts, with an accurate and complete exposition of them; complete, namely, so far as is possible in the present state of our knowledge of its elements. But there is another thing to be attended to which is of a more philosophical and architectonic character, namely, to grasp correctly the idea of the whole, and from thence to get a view of all those parts as mutually related by the aid of pure reason, and by means of their derivation from the concept of the whole. This is only possible through the most intimate acquaintance with the system; and those who find the first inquiry too troublesome, and do not think it worth their while to attain such an acquaintance, cannot reach the second stage, namely, the general view, which is a synthetical return to that which had previously been given analytically. It is no wonder then if they find inconsistencies everywhere, although the gaps which these indicate are not in the system itself, but in their own incoherent train of thought.

I have no fear, as regards this treatise, of the reproach that I wish to introduce a new language, since the sort of knowledge here in question has itself somewhat of an everyday character. Nor even in the case of the former critique could this reproach occur to anyone who had thought it through and not merely turned over the leaves. To invent new words where the language has no lack of expressions for given notions is a childish effort to distinguish oneself from the crowd, if not by new and true thoughts, yet by new patches on the old garment. If, therefore, the readers of that work know any more familiar expressions which are as suitable to the thought as those seem to me to be, or if they think they can show the futility of these thoughts themselves and hence that of the expression, they would, in the first case, very much oblige me, for I only desire to be understood: and, in the second case, they would deserve well of philosophy. But, as long as these thoughts stand, I very much doubt that suitable and yet more common expressions for them can be found. *

PREFACE ^paragraph 25

* I am more afraid in the present treatise of occasional
misconception in respect of some expressions which I have
chosen with the greatest care in order that the notion to
which they point may not be missed. Thus, in the table of
categories of the Practical reason under the title of
Modality, the Permitted, and forbidden (in a practical
objective point of view, possible and impossible) have
almost the same meaning in common language as the next
category, duty and contrary to duty. Here, however, the
former means what coincides with, or contradicts, a merely
possible practical precept (for example, the solution of all
problems of geometry and mechanics); the latter, what is
similarly related to a law actually present in the reason;
and this distinction is not quite foreign even to common
language, although somewhat unusual. For example, it is
forbidden to an orator, as such, to forge new words or
constructions; in a certain degree this is permitted to a
poet; in neither case is there any question of duty. For if
anyone chooses to forfeit his reputation as an orator, no
one can prevent him. We have here only to do with the
distinction of imperatives into problematical, assertorial,
and apodeictic. Similarly in the note in which I have pared
the moral ideas of practical perfection in different
philosophical schools, I have distinguished the idea of
wisdom from that of holiness, although I have stated that
essentially and objectively they are the same. But in that
place I understand by the former only that wisdom to which
man (the Stoic) lays claim; therefore I take it subjectively
as an attribute alleged to belong to man. (Perhaps the
expression virtue, with which also the Stoic made great
show, would better mark the characteristic of his school.)
The expression of a postulate of pure practical reason might
give most occasion to misapprehension in case the reader
confounded it with the signification of the postulates in
pure mathematics, which carry apodeictic certainty with
them. These, however, postulate the possibility of an
action, the object of which has been previously recognized a
priori in theory as possible, and that with perfect
certainty. But the former postulates the possibility of an
object itself (God and the immortality of the soul) from
apodeictic practical laws, and therefore only for the
purposes of a practical reason. This certainty of the
postulated possibility then is not at all theoretic, and
consequently not apodeictic; that is to say, it is not a
known necessity as regards the object, but a necessary
supposition as regards the subject, necessary for the
obedience to its objective but practical laws. It is,
therefore, merely a necessary hypothesis. I could find no
better expression for this rational necessity, which is
subjective, but yet true and unconditional.

In this manner, then, the a priori principles of two faculties of the mind, the faculty of cognition and that of desire, would be found and determined as to the conditions, extent, and limits of their use, and thus a sure foundation be paid for a scientific system of philosophy, both theoretic and practical.

Nothing worse could happen to these labours than that anyone should make the unexpected discovery that there neither is, nor can be, any a priori knowledge at all. But there is no danger of this. This would be the same thing as if one sought to prove by reason that there is no reason. For we only say that we know something by reason, when we are conscious that we could have known it, even if it had not been given to us in experience; hence rational knowledge and knowledge a priori are one and the same. It is a clear contradiction to try to extract necessity from a principle of experience (ex pumice aquam), and to try by this to give a judgement true universality (without which there is no rational inference, not even inference from analogy, which is at least a presumed universality and objective necessity). To substitute subjective necessity, that is, custom, for objective, which exists only in a priori judgements, is to deny to reason the power of judging about the object, i.e., of knowing it, and what belongs to it. It implies, for example, that we must not say of something which often or always follows a certain antecedent state that we can conclude from this to that (for this would imply objective necessity and the notion of an a priori connexion), but only that we may expect similar cases (just as animals do), that is that we reject the notion of cause altogether as false and a mere delusion. As to attempting to remedy this want of objective and consequently universal validity by saying that we can see no ground for attributing any other sort of knowledge to other rational beings, if this reasoning were valid, our ignorance would do more for the enlargement of our knowledge than all our meditation. For, then, on this very ground that we have no knowledge of any other rational beings besides man, we should have a right to suppose them to be of the same nature as we know ourselves to be: that is, we should really know them. I omit to mention that universal assent does not prove the objective validity of a judgement (i.e., its validity as a cognition), and although this universal assent should accidentally happen, it could furnish no proof of agreement with the object; on the contrary, it is the objective validity which alone constitutes the basis of a necessary universal consent.