representations of space and time。 and from the elementary conceptions
of the understanding。
This attempt to introduce a plete revolution in the procedure
of metaphysics； after the example of the geometricians and natural
philosophers； constitutes the aim of the Critique of Pure
Speculative Reason。 It is a treatise on the method to be followed； not
a system of the science itself。 But； at the same time； it marks out
and defines both the external boundaries and the internal structure of
this science。 For pure speculative reason has this peculiarity；
that； in choosing the various objects of thought； it is able to define
the limits of its own faculties； and even to give a plete
enumeration of the possible modes of proposing problems to itself； and
thus to sketch out the entire system of metaphysics。 For； on the one
hand； in cognition a priori； nothing must be attributed to the objects
but what the thinking subject derives from itself； and； on the other
hand； reason is； in regard to the principles of cognition； a perfectly
distinct； independent unity； in which； as in an organized body；
every member exists for the sake of the others； and all for the sake
of each； so that no principle can be viewed； with safety； in one
relationship； unless it is； at the same time； viewed in relation to
the total use of pure reason。 Hence； too； metaphysics has this
singular advantage… an advantage which falls to the lot of no other
science which has to do with objects… that； if once it is conducted
into the sure path of science； by means of this criticism； it can then
take in the whole sphere of its cognitions； and can thus plete
its work； and leave it for the use of posterity； as a capital which
can never receive fresh accessions。 For metaphysics has to deal only
with principles and with the limitations of its own employment as
determined by these principles。 To this perfection it is； therefore；
bound； as the fundamental science； to attain； and to it the maxim
may justly be applied：
Nil actum reputans； si quid superesset agendum。*
*〃He considered nothing done； so long as anything remained to be
done。〃
But； it will be asked； what kind of a treasure is this that we
propose to bequeath to posterity？ What is the real value of this
system of metaphysics； purified by criticism； and thereby reduced to a
permanent condition？ A cursory view of the present work will lead to
the supposition that its use is merely negative； that it only serves
to warn us against venturing； with speculative reason； beyond the
limits of experience。 This is； in fact； its primary use。 But this；
at once； assumes a positive value； when we observe that the principles
with which speculative reason endeavours to transcend its limits
lead inevitably； not to the extension； but to the contraction of the
use of reason； inasmuch as they threaten to extend the limits of
sensibility； which is their proper sphere； over the entire realm of
thought and； thus； to supplant the pure （practical） use of reason。
So far； then； as this criticism is occupied in confining speculative
reason within its proper bounds； it is only negative； but； inasmuch as
it thereby； at the same time； removes an obstacle which impedes and
even threatens to destroy the use of practical reason； it possesses
a positive and very important value。 In order to admit this； we have
only to be convinced that there is an absolutely necessary use of pure
reason… the moral use… in which it inevitably transcends the limits of
sensibility； without the aid of speculation； requiring only to be
insured against the effects of a speculation which would involve it in
contradiction with itself。 To deny the positive advantage of the
service which this criticism renders us would be as absurd as。 to
maintain that the system of police is productive of no positive
benefit； since its main business is to prevent the violence which
citizen has to apprehend from citizen； that so each may pursue his
vocation in peace and security。 That space and time are only forms
of sensible intuition； and hence are only conditions of the
existence of things as phenomena； that； moreover； we have no
conceptions of the understanding； and； consequently； no elements for
the cognition of things； except in so far as a corresponding intuition
can be given to these conceptions； that； accordingly； we can have no
cognition of an object； as a thing in itself； but only as an object of
sensible intuition； that is； as phenomenon… all this is proved in
the analytical part of the Critique； and from this the limitation of
all possible speculative cognition to the mere objects of
experience； follows as a necessary result。 At the same time； it must
be carefully borne in mind that； while we surrender the power of
cognizing； we still reserve the power of thinking objects； as things
in themselves。* For； otherwise； we should require to affirm the
existence of an appearance； without something that appears… which
would be absurd。 Now let us suppose； for a moment； that we had not
undertaken this criticism and； accordingly； had not drawn the
necessary distinction between things as objects of experience and
things as they are in themselves。 The principle of causality； and；
by consequence； the mechanism of nature as determined by causality；
would then have absolute validity in relation to all things as
efficient causes。 I should then be unable to assert； with regard to
one and the same being； e。g。； the human soul； that its will is free；
and yet； at the same time； subject to natural necessity； that is；
not free； without falling into a palpable contradiction； for in both
propositions I should take the soul in the same signification； as a
thing in general； as a thing in itself… as； without previous
criticism； I could not but take it。 Suppose now； on the other hand；
that we have undertaken this criticism； and have learnt that an object
may be taken in two senses； first； as a phenomenon； secondly； as a
thing in itself； and that； according to the deduction of the
conceptions of the understanding； the principle of causality has
reference only to things in the first sense。 We then see how it does
not involve any contradiction to assert； on the one hand； that the
will； in the phenomenal sphere… in visible action… is necessarily
obedient to the law of nature； and； in so far； not free； and； on the
other hand； that； as belonging to a thing in itself； it is not subject
to that law； and； accordingly； is free。 Now； it is true that I cannot；
by means of speculative reason； and still less by empirical
observation； cognize my soul as a thing in itself and consequently；
cannot cognize liberty as the property of a being to which I ascribe
effects in the world of sense。 For； to do so； I must cognize this
being as existing； and yet not in time； which… since I cannot
support my conception by any intuition… is impossible。 At the same
time； while I cannot cognize； I can quite well think freedom； that
is to say； my representation of it involves at least no contradiction；
if we bear in mind the critical distinction of the two modes of
representation （the sensible and the intellectual） and the
consequent limitation of the conceptions of the pure understanding and
of the principles which flow from them。 Suppose now that morality
necessarily presupposed liberty； in the strictest sense； as a property
of our will； suppose that reason contained certain practical； original
principles a priori； which were absolutely impossible without this
presupposition； and suppose； at the same time； that speculative reason
had proved that liberty was incapable of being thought at all。 It
would then follow that the moral presupposition must give way to the
speculative affirmation； the opposite of which involves an obvious
contradiction； and that liberty and； with it； morality must yield to
the mechanism of nature； for the negation of morality involves no
contradiction； except on the presupposition of liberty。 Now morality
does not require the speculative cognition of liberty； it is enough
that I can think it； that its conception involves no contradiction；
that it does not interfere with the mechanism of nature。 But even this
requirement we could not satisfy； if we had not learnt the twofold
sense in which things may be taken； and it is only in this way that
the doctrine of morality and the doctrine of nature are confined
within their proper limits。 For this result； then； we are indebted
to a criticism which warns us of our unavoidable ignorance with regard
to things in themselves； and establishes the necessary limitation of
our theoretical cognition to mere phenomena。
*In order to cognize an object； I must be able to prove its
possibility； either from its reality as attested by experience； or a
priori； by means of reason。 But I can think what I please； provided
only I do not contradict myself； that is； provided my conception is
a possible thought； though I may be unable to answer for the existence
of a corresponding object in the sum of possibilities。 But something
more is required before I can attribute to such a conception objective
validity； that is real possibility… the other possibility being merely