THE CRITIQUE OF PRACTICAL REASON
by Immanuel Kant
translated by Thomas Kingsmill Abbott
PREFACE
PREFACE。
This work is called the Critique of Practical Reason； not of the
pure practical reason； although its parallelism with the speculative
critique would seem to require the latter term。 The reason of this
appears sufficiently from the treatise itself。 Its business is to show
that there is pure practical reason； and for this purpose it
criticizes the entire practical faculty of reason。 If it succeeds in
this； it has no need to criticize the pure faculty itself in order
to see whether reason in making such a claim does not presumptuously
overstep itself （as is the case with the speculative reason）。 For
if； as pure reason； it is actually practical； it proves its own
reality and that of its concepts by fact； and all disputation
against the possibility of its being real is futile。
With this faculty； transcendental freedom is also established；
freedom； namely； in that absolute sense in which speculative reason
required it in its use of the concept of causality in order to
escape the antinomy into which it inevitably falls； when in the
chain of cause and effect it tries to think the unconditioned。
Speculative reason could only exhibit this concept （of freedom）
problematically as not impossible to thought； without assuring it
any objective reality； and merely lest the supposed impossibility of
what it must at least allow to be thinkable should endanger its very
being and plunge it into an abyss of scepticism。
Inasmuch as the reality of the concept of freedom is proved by an
apodeictic law of practical reason； it is the keystone of the whole
system of pure reason； even the speculative； and all other concepts
（those of God and immortality） which； as being mere ideas； remain in
it unsupported； now attach themselves to this concept； and by it
obtain consistence and objective reality； that is to say； their
possibility is proved by the fact that freedom actually exists； for
this idea is revealed by the moral law。
Freedom； however； is the only one of all the ideas of the
speculative reason of which we know the possibility a priori （without；
however； understanding it）； because it is the condition of the moral
law which we know。* The ideas of God and immortality； however； are not
conditions of the moral law； but only conditions of the necessary
object of a will determined by this law； that is to say； conditions of
the practical use of our pure reason。 Hence； with respect to these
ideas； we cannot affirm that we know and understand； I will not say
the actuality； but even the possibility of them。 However they are
the conditions of the application of the morally determined will to
its object； which is given to it a priori； viz。； the summum bonum。
Consequently in this practical point of view their possibility must be
assumed； although we cannot theoretically know and understand it。 To
justify this assumption it is sufficient； in a practical point of
view； that they contain no intrinsic impossibility （contradiction）。
Here we have what； as far as speculative reason is concerned； is a
merely subjective principle of assent； which； however； is
objectively valid for a reason equally pure but practical； and this
principle； by means of the concept of freedom； assures objective
reality and authority to the ideas of God and immortality。 Nay；
there is a subjective necessity （a need of pure reason） to assume
them。 Nevertheless the theoretical knowledge of reason is not hereby
enlarged； but only the possibility is given； which heretofore was
merely a problem and now bees assertion； and thus the practical use
of reason is connected with the elements of theoretical reason。 And
this need is not a merely hypothetical one for the arbitrary
purposes of speculation； that we must assume something if we wish in
speculation to carry reason to its utmost limits； but it is a need
which has the force of law to assume something without which that
cannot be which we must inevitably set before us as the aim of our
action。
*Lest any one should imagine that he finds an inconsistency here
when I call freedom the condition of the moral law； and hereafter
maintain in the treatise itself that the moral law is the condition
under which we can first bee conscious of freedom； I will merely
remark that freedom is the ratio essendi of the moral law； while the
moral law is the ratio cognoscendi of freedom。 For Pad not the moral
law been previously distinctly thought in our reason； we should
never consider ourselves justified in assuming such a thing as
freedom； although it be not contradictory。 But were there no freedom
it would be impossible to trace the moral law in ourselves at all。
It would certainly be more satisfactory to our speculative reason if
it could solve these problems for itself without this circuit and
preserve the solution for practical use as a thing to be referred
to； but in fact our faculty of speculation is not so well provided。
Those who boast of such high knowledge ought not to keep it back；
but to exhibit it publicly that it may be tested and appreciated。 They
want to prove： very good； let them prove； and the critical
philosophy lays its arms at their feet as the victors。 Quid statis？
Nolint。 Atqui licet esse beatis。 As they then do not in fact choose to
do so； probably because they cannot； we must take up these arms
again in order to seek in the mortal use of reason； and to base on
this； the notions of God； freedom； and immortality； the possibility of
which speculation cannot adequately prove。
Here first is explained the enigma of the critical philosophy； viz。：
how we deny objective reality to the supersensible use of the
categories in speculation and yet admit this reality with respect to
the objects of pure practical reason。 This must at first seem
inconsistent as long as this practical use is only nominally known。
But when； by a thorough analysis of it； one bees aware that the
reality spoken of does not imply any theoretical determination of
the categories and extension of our knowledge to the supersensible；
but that what is meant is that in this respect an object belongs to
them； because either they are contained in the necessary determination
of the will a priori； or are inseparably connected with its object；
then this inconsistency disappears； because the use we make of these
concepts is different from what speculative reason requires。 On the
other hand； there now appears an unexpected and very satisfactory
proof of the consistency of the speculative critical philosophy。 For
whereas it insisted that the objects of experience as such；
including our own subject； have only the value of phenomena； while
at the same time things in themselves must be supposed as their basis；
so that not everything supersensible was to be regarded as a fiction
and its concept as empty； so now practical reason itself； without
any concert with the speculative； assures reality to a supersensible
object of the category of causality； viz。； freedom； although （as
bees a practical concept） only for practical use； and this
establishes on the evidence of a fact that which in the former case
could only be conceived。 By this the strange but certain doctrine of
the speculative critical philosophy； that the thinking subject is to
itself in internal intuition only a phenomenon； obtains in the
critical examination of the practical reason its full confirmation；
and that so thoroughly that we should be pelled to adopt this
doctrine； even if the former had never proved it at all。*
*The union of causality as freedom with causality as rational
mechanism； the former established by the moral law； the latter by
the law of nature in the same subject； namely； man； is impossible；
unless we conceive him with reference to the former as a being in
himself； and with reference to the latter as a phenomenon… the
former in pure consciousness； the latter in empirical consciousness。
Otherwise reason inevitably contradicts itself。
By this also I can understand why the most considerable objections
which I have as yet met with against the Critique turn about these two
points； namely； on the one side； the objective reality of the
categories as applied to noumena； which is in the theoretical
department of knowledge denied； in the practical affirmed； and on
the other side； the paradoxical demand to regard oneself qua subject
of freedom as a noumenon； and at the same time from the point of
view of physical nature as a phenomenon in one's own empirical
consciousness； for as long as one has formed no definite notions of
morality and freedom； one could not conjecture on the one side what
was intended to be the noumenon； the basis of the alleged
phenomenon； and on the other side it seemed doubtful whether it was at
all possible to form any notion of it； seeing that we had previously
assigned all the notions of the pure understanding in its
theoretical use exclusively to phenomena。 Nothing but a detailed
criticism of the practical reason can remove all this
misapprehension