Critique of Pure Reason (Preface to Second Edition)

Immanuel Kant's
Critique
trans. by Norman Kemp Smith
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PREFACE TO THE SECOND EDITION
WHETHER the treatment of such knowledge as lies within the
province of reason does or does not follow the secure path of a
science, is easily to be determined from the outcome. For if
after elaborate preparations, frequently renewed, it is brought
to a stop immediately it nears its goal; if often it is 
compelled to retrace its steps and strike into some new line of
approach; or again, if the various participants are unable to
agree in any common plan of procedure, then we may rest
assured that it is very far from having entered upon the secure
path of a science, and is indeed a merely random groping. In
these circumstances, we shall be rendering a service to reason
should we succeed in discovering the path upon which it can
securely travel, even if, as a result of so doing, much that is
comprised in our original aims, adopted without reflection,
may have to be abandoned as fruitless.
That logic has already, from the earliest times, proceeded
upon this sure path is evidenced by the fact that since Aristotle
it has not required to retrace a single step, unless, indeed,
we care to count as improvements the removal of certain needless
subtleties or the clearer exposition of its recognised teaching,
features which concern the elegance rather than the certainty
of the science. It is remarkable also that to the present
day this logic has not been able to advance a single step, and
is thus to all appearance a closed and completed body of 
doctrine. If some of the moderns have thought to enlarge it by
introducing psychological chapters on the different faculties of
knowledge (imagination, wit, etc. ), metaphysical chapters on
the origin of knowledge or on the different kinds of certainty
according to difference in the objects (idealism, scepticism, etc. ),
or anthropological chapters on prejudices, their causes and
remedies, this could only arise from their ignorance of the
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peculiar nature of logical science. We do not enlarge but
disfigure sciences, if we allow them to trespass upon one
another's territory. The sphere of logic is quite precisely 
delimited; its sole concern is to give an exhaustive exposition and
a strict proof of the formal rules of all thought, whether it be
a priori or empirical, whatever be its origin or its object, and
whatever hindrances, accidental or natural, it may encounter
in our minds.
That logic should have been thus successful is an advantage
which it owes entirely to its limitations, whereby it is
justified in abstracting -- indeed, it is under obligation to do
so -- from all objects of knowledge and their differences, leaving
the understanding nothing to deal with save itself and its
form. But for reason to enter on the sure path of science is,
of course, much more difficult, since it has to deal not with
itself alone but also with objects. Logic, therefore, as a 
propaedeutic, forms, as it were, only the vestibule of the sciences;
and when we are concerned with specific modes of knowledge,
while logic is indeed presupposed in any critical
estimate of them, yet for the actual acquiring of them we
have to look to the sciences properly and objectively so
called.
Now if reason is to be a factor in these sciences, something
in them must be known a priori, and this knowledge may be
related to its object in one or other of two ways, either as
merely determining it and its concept (which must be supplied
from elsewhere) or as also making it actual. The former is
theoretical, the latter practical knowledge of reason. In both,
that part in which reason determines its object completely
a priori, namely, the pure part -- however much or little this part
may contain -- must be first and separately dealt with, in case
it be confounded with what comes from other sources. For it
is bad management if we blindly pay out what comes in, and
are not able, when the income falls into arrears, to distinguish
which part of it can justify expenditure, and in which line we
must make reductions.
Mathematics and physics, the two sciences in which reason
yields theoretical knowledge, have to determine their objects
a priori, the former doing so quite purely, the latter having
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to reckon, at least partially, with sources of knowledge other
than reason.
In the earliest times to which the history of human reason
extends, mathematics, among that wonderful people, the
Greeks, had already entered upon the sure path of science. But
it must not be supposed that it was as easy for mathematics as
it was for logic -- in which reason has to deal with itself alone --
to light upon, or rather to construct for itself, that royal road.
On the contrary, I believe that it long remained, especially
among the Egyptians, in the groping stage, and that the 
transformation must have been due to a revolution brought about
by the happy thought of a single man, the experiment which
he devised marking out the path upon which the science must
enter, and by following which, secure progress throughout all
time and in endless expansion is infallibly secured. The history
of this intellectual revolution -- far more important than
the discovery of the passage round the celebrated Cape of
Good Hope -- and of its fortunate author, has not been 
preserved. But the fact that Diogenes Laertius, in handing down
an account of these matters, names the reputed author of even
the least important among the geometrical demonstrations,
even of those which, for ordinary consciousness, stand in need
of no such proof, does at least show that the memory of the
revolution, brought about by the first glimpse of this new path,
must have seemed to mathematicians of such outstanding importance
as to cause it to survive the tide of oblivion. A new light
flashed upon the mind of the first man (be he Thales or some
other) who demonstrated the properties of the isosceles triangle.
The true method, so he found, was not to inspect what he discerned
either in the figure, or in the bare concept of it, and from
this, as it were, to read off its properties; but to bring out what
was necessarily implied in the concepts that he had himself
formed a priori, and had put into the figure in the construction
by which he presented it to himself. If he is to know anything
with a priori certainty he must not ascribe to the figure 
anything save what necessarily follows from what he has himself
set into it in accordance with his concept.
Natural science was very much longer in entering upon the
highway of science. It is, indeed, only about a century and a
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half since Bacon, by his ingenious proposals, partly initiated
this discovery, partly inspired fresh vigour in those who were
already on the way to it. In this case also the discovery can
be explained as being the sudden outcome of an intellectual
revolution. In my present remarks I am referring to natural
science only in so far as it is founded on empirical principles.
When Galileo caused balls, the weights of which he had
himself previously determined, to roll down an inclined plane;
when Torricelli made the air carry a weight which he had 
calculated beforehand to be equal to that of a definite column of
water; or in more recent times, when Stahl changed metal
into lime, and lime back into metal, by withdrawing something
and then restoring it, a light broke upon all students of
nature. They learned that reason has insight only into that
which it produces after a plan of its own, and that it must not
allow itself to be kept, as it were, in nature's leading-strings,
but must itself show the way with principles of judgment based
upon fixed laws, constraining nature to give answer to 
questions of reason's own determining. Accidental observations,
made in obedience to no previously thought-out plan, can
never be made to yield a necessary law, which alone reason is
concerned to discover. Reason, holding in one hand its 
principles, according to which alone concordant appearances can
be admitted as equivalent to laws, and in the other hand the
experiment which it has devised in conformity with these 
principles, must approach nature in order to be taught by it. It
must not, however, do so in the character of a pupil who
listens to everything that the teacher chooses to say, but of
an appointed judge who compels the witnesses to answer
questions which he has himself formulated. Even physics,
therefore, owes the beneficent revolution in its point of view
entirely to the happy thought, that while reason must seek in
nature, not fictitiously ascribe to it, whatever as not being
knowable through reason's own resources has to be learnt,
if learnt at all, only from nature, it must adopt as its guide,
in so seeking, that which it has itself put into nature. It is thus
that the study of nature has entered on the secure path of a
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science, after having for so many centuries been nothing but
a process of merely random groping.
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 I am not, in my choice of examples, tracing the exact course of
the history of the experimental method; we have indeed no very 
precise knowledge of its first beginnings.
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Metaphysics is a completely isolated speculative science of
reason, which soars far above the teachings of experience, and
in which reason is indeed meant to be its own pupil. Metaphysics
rests on concepts alone -- not, like mathematics, on their
application to intuition. But though it is older than all other
sciences, and would survive even if all the rest were swallowed
up in the abyss of an all-destroying barbarism, it has not yet
had the good fortune to enter upon the secure path of a science.
For in it reason is perpetually being brought to a stand, even
when the laws into which it is seeking to have, as it professes,
an a priori insight are those that are confirmed by our most 
common experiences. Ever and again we have to retrace our steps,
as not leading us in the direction in which we desire to go. So
far, too, are the students of metaphysics from exhibiting any
kind of unanimity in their contentions, that metaphysics has
rather to be regarded as a battle-ground quite peculiarly suited
for those who desire to exercise themselves in mock combats,
and in which no participant has ever yet succeeded in gaining
even so much as an inch of territory, not at least in such
manner as to secure him in its permanent possession. This
shows, beyond all questioning, that the procedure of 
metaphysics has hitherto been a merely random groping, and,
what is worst of all, a groping among mere concepts.
What, then, is the reason why, in this field, the sure road
to science has not hitherto been found? Is it, perhaps, 
impossible of discovery? Why, in that case, should nature have
visited our reason with the restless endeavour whereby it is
ever searching for such a path, as if this were one of its most
important concerns. Nay, more, how little cause have we to
place trust in our reason, if, in one of the most important
domains of which we would fain have knowledge, it does
not merely fail us, but lures us on by deceitful promises, and
in the end betrays us! Or if it be only that we have thus far
failed to find the true path, are there any indications to justify
the hope that by renewed efforts we may have better fortune
than has fallen to our predecessors?
The examples of mathematics and natural science, which
by a single and sudden revolution have become what they
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now are, seem to me sufficiently remarkable to suggest our
considering what may have been the essential features in the
changed point of view by which they have so greatly benefited.
Their success should incline us, at least by way of experiment,
to imitate their procedure, so far as the analogy which,
as species of rational knowledge, they bear to metaphysics may
permit. Hitherto it has been assumed that all our knowledge
must conform to objects. But all attempts to extend our 
knowledge of objects by establishing something in regard to them
a priori, by means of concepts, have, on this assumption,
ended in failure. We must therefore make trial whether we
may not have more success in the tasks of metaphysics, if
we suppose that objects must conform to our knowledge. This
would agree better with what is desired, namely, that it should
be possible to have knowledge of objects a priori, determining
something in regard to them prior to their being given. We
should then be proceeding precisely on the lines of Copernicus'
primary hypothesis. Failing of satisfactory progress in 
explaining the movements of the heavenly bodies on the supposition
that they all revolved round the spectator, he tried whether
he might not have better success if he made the spectator
to revolve and the stars to remain at rest. A similar experiment
can be tried in metaphysics, as regards the intuition
of objects. If intuition must conform to the constitution of
the objects, I do not see how we could know anything of
the latter a priori; but if the object (as object of the senses)
must conform to the constitution of our faculty of intuition,
I have no difficulty in conceiving such a possibility. Since I
cannot rest in these intuitions if they are to become known,
but must relate them as representations to something as their
object, and determine this latter through them, either I must
assume that the concepts, by means of which I obtain this
determination, conform to the object, or else I assume that the
objects, or what is the same thing, that the experience in
which alone, as given objects, they can be known, conform to
the concepts. In the former case, I am again in the same 
perplexity as to how I can know anything a priori in regard to
the objects. In the latter case the outlook is more hopeful. For
experience is itself a species of knowledge which involves
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understanding; and understanding has rules which I must 
presuppose as being in me prior to objects being given to me, and
therefore as being a priori. They find expression in a priori
concepts to which all objects of experience necessarily 
conform, and with which they must agree. As regards objects
which are thought solely through reason, and indeed as
necessary, but which can never -- at least not in the manner
in which reason thinks them -- be given in experience, the
attempts at thinking them (for they must admit of being
thought) will furnish an excellent touchstone of what we are
adopting as our new method of thought, namely, that we can
know a priori of things only what we ourselves put into them.
This experiment succeeds as well as could be desired, and
promises to metaphysics, in its first part -- the part that is
occupied with those concepts a priori to which the corresponding
objects, commensurate with them, can be given in experience
-- the secure path of a science. For the new point of
view enables us to explain how there can be knowledge
a priori; and, in addition, to furnish satisfactory proofs of the
laws which form the a priori basis of nature, regarded as the
sum of the objects of experience -- neither achievement being
possible on the procedure hitherto followed.
 This method, modelled on that of the student of nature, consists
in looking for the elements of pure reason in what admits of 
confirmation or refutation by experiment. Now the propositions of pure
reason, especially if they venture out beyond all limits of possible
experience, cannot be brought to the test through any experiment
with their objects, as in natural science. In dealing with those concepts
and principles which we adopt a priori, all that we can do is to
contrive that they be used for viewing objects from two different
points of view -- on the one hand, in connection with experience, as
objects of the senses and of the understanding, and on the other
hand, for the isolated reason that strives to transcend all limits of
experience, as objects which are thought merely. If, when things are
viewed from this twofold standpoint, we find that there is agreement
with the principle of pure reason, but that when we regard them
only from a single point of view reason is involved in unavoidable
self-conflict, the experiment decides in favour of the correctness of
this distinction.
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But this deduction
of our power of knowing a priori, in the first part of metaphysics,
has a consequence which is startling, and which has the appearance
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of being highly prejudicial to the whole purpose of metaphysics,
as dealt with in the second part. For we are brought
to the conclusion that we can never transcend the limits of
possible experience, though that is precisely what this science
is concerned, above all else, to achieve. This situation yields,
however, just the very experiment by which, indirectly, we
are enabled to prove the truth of this first estimate of our
a priori knowledge of reason, namely, that such knowledge
has to do only with appearances, and must leave the thing
in itself as indeed real per se, but as not known by us.
For what necessarily forces us to transcend the limits of
experience and of all appearances is the unconditioned,
which reason, by necessity and by right, demands in things
in themselves, as required to complete the series of conditions.
If, then, on the supposition that our empirical knowledge
conforms to objects as things in themselves, we find
that the unconditioned cannot be thought without contradiction,
and that when, on the other hand, we suppose that our 
representation of things, as they are given to us, does not conform
to these things as they are in themselves, but that these objects,
as appearances, conform to our mode of representation, the
contradiction vanishes; and if, therefore, we thus find that
the unconditioned is not to be met with in things, so far as
we know them, that is, so far as they are given to us, but
only so far as we do not know them, that is, so far as they
are things in themselves, we are justified in concluding that
what we at first assumed for the purposes of experiment is
now definitely confirmed.
 This experiment of pure reason bears a great similarity to what
in chemistry is sometimes entitled the experiment of reduction, or
more usually the synthetic process. The analysis of the metaphysician
separates pure a priori knowledge into two very heterogeneous
elements, namely, the knowledge of things as appearances, and the
knowledge of things in themselves; his dialectic combines these
two again, in harmony with the necessary idea of the unconditioned
demanded by reason, and finds that this harmony can never be 
obtained except through the above distinction, which must therefore
be accepted.
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But when all progress in the field
of the supersensible has thus been denied to speculative
reason, it is still open to us to enquire whether, in the practical
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knowledge of reason, data may not be found sufficient to 
determine reason's transcendent concept of the unconditioned,
and so to enable us, in accordance with the wish of metaphysics,
and by means of knowledge that is possible a priori,
though only from a practical point of view, to pass beyond
the limits of all possible experience. Speculative reason has
thus at least made room for such an extension; and if it must
at the same time leave it empty, yet none the less we are at
liberty, indeed we are summoned, to take occupation of it,
if we can, by practical data of reason.
This attempt to alter the procedure which has hitherto
prevailed in metaphysics, by completely revolutionising it
in accordance with the example set by the geometers and
physicists, forms indeed the main purpose of this critique of
pure speculative reason. It is a treatise on the method, not a
system of the science itself. But at the same time it marks out
the whole plan of the science, both as regards its limits and as
regards its entire internal structure. For pure speculative reason
has this peculiarity, that it can measure its powers according
to the different ways in which it chooses the objects of its
thinking, and can also give an exhaustive enumeration of
the various ways in which it propounds its problems, and so
is able, nay bound, to trace the complete outline of a system
of metaphysics. As regards the first point, nothing in a priori
knowledge can be ascribed to objects save what the thinking
subject derives from itself;
 Similarly, the fundamental laws of the motions of the heavenly
bodies gave established certainty to what Copernicus had at first
assumed only as an hypothesis, and at the same time yielded
proof of the invisible force (the Newtonian attraction) which holds
the universe together. The latter would have remained for ever 
undiscovered if Copernicus had not dared, in a manner contradictory
of the senses, but yet true, to seek the observed movements, not in
the heavenly bodies, but in the spectator. The change in point of
view, analogous to this hypothesis, which is expounded in the
Critique, I put forward in this preface as an hypothesis only, in order
to draw attention to the character of these first attempts at such a
change, which are always hypothetical. But in the Critique itself it
will be proved, apodeictically not hypothetically, from the nature
of our representations of space and time and from the elementary
concepts of the understanding.
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 as regards the second point, pure
reason, so far as the principles of its knowledge are concerned,
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is a quite separate self-subsistent unity, in which, as in an
organised body, every member exists for every other, and
all for the sake of each, so that no principle can safely be
taken in any one relation, unless it has been investigated in
the entirety of its relations to the whole employment of pure
reason. Consequently, metaphysics has also this singular
advantage, such as falls to the lot of no other science which
deals with objects (for logic is concerned only with the form
of thought in general), that should it, through this critique,
be set upon the secure path of a science, it is capable of 
acquiring exhaustive knowledge of its entire field. Metaphysics
has to deal only with principles, and with the limits of their
employment as determined by these principles themselves,
and it can therefore finish its work and bequeath it to posterity
as a capital to which no addition can be made. Since it is
a fundamental science, it is under obligation to achieve this
completeness. We must be able to say of it: nil actum 
reputans, si quid superesset agendum.
But, it will be asked, what sort of a treasure is this that
we propose to bequeath to posterity? What is the value of
the metaphysics that is alleged to be thus purified by criticism
and established once for all? On a cursory view of the
present work it may seem that its results are merely negative,
warning us that we must never venture with speculative reason
beyond the limits of experience. Such is in fact its primary use.
But such teaching at once acquires a positive value when we
recognise that the principles with which speculative reason
ventures out beyond its proper limits do not in effect extend
the employment of reason, but, as we find on closer scrutiny,
inevitably narrow it. These principles properly belong [not
to reason but] to sensibility, and when thus employed they
threaten to make the bounds of sensibility coextensive with
the real, and so to supplant reason in its pure (practical) 
employment. So far, therefore, as our Critique limits speculative
reason, it is indeed negative; but since it thereby removes an
obstacle which stands in the way of the employment of practical
reason, nay threatens to destroy it, it has in reality a positive
and very important use. At least this is so, immediately
we are convinced that there is an absolutely necessary 
practical employment of pure reason -- the moral -- in which it
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inevitably goes beyond the limits of sensibility. Though
[practical] reason, in thus proceeding, requires no assistance
from speculative reason, it must yet be assured against its
opposition, that reason may not be brought into conflict
with itself. To deny that the service which the Critique renders
is Positive in character, would thus be like saying that the
police are of no positive benefit, inasmuch as their main business
is merely to prevent the violence of which citizens stand
in mutual fear, in order that each may pursue his vocation in
peace and security. That space and time are only forms of sensible
intuition, and so only conditions of the existence of things
as appearances; that, moreover, we have no concepts of 
understanding, and consequently no elements for the knowledge of
things, save in so far as intuition can be given corresponding
to these concepts; and that we can therefore have no knowledge
of any object as thing in itself, but only in so far as it is an
object of sensible intuition, that is, an appearance -- all this is
proved in the analytical part of the Critique. Thus it does 
indeed follow that all possible speculative knowledge of reason
is limited to mere objects of experience. But our further 
contention must also be duly borne in mind, namely, that though
We cannot know these objects as things in themselves, we
must yet be in position at least to think them as things in 
themselves; otherwise we should be landed in the absurd conclusion
that there can be appearance without anything that appears.
Now let us suppose that the distinction, which our Critique has
shown to be necessary, between things as objects of experience
and those same things as things in themselves, had not been
made.
 To know an object I must be able to prove its possibility, either
from its actuality as attested by experience, or a priori by means of
reason. But I can think whatever I please, provided only that I do
not contradict myself, that is, provided my concept is a possible
thought. This suffices for the possibility of the concept, even though
I may not be able to answer for there being, in the sum of all 
possibilities, an object corresponding to it. But something more is 
required before I can ascribe to such a concept objective validity, that
is, real possibility; the former possibility is merely logical. This 
something more need not, however, be sought in the theoretical sources of
knowledge; it may lie in those that are practical.
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In that case all things in general, as far as they are
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efficient causes, would be determined by the principle of 
causality and consequently by the mechanism of nature. I could
not, therefore, without palpable contradiction, say of one and
the same being, for instance the human soul, that its will is free
and yet is subject to natural necessity, that is, is not free. For
I have taken the soul in both propositions in one and the same
sense, namely as a thing in general, that is, as a thing in itself;
and save by means of a preceding critique, could not have done
otherwise. But if our Critique is not in error in teaching that
the object is to be taken in a twofold sense, namely as appearance
and as thing in itself; if the deduction of the concepts of
understanding is valid, and the principle of causality therefore
applies only to things taken in the former sense, namely,
in so far as they are objects of experience -- these same objects,
taken in the other sense, not being subject to the principle --
then there is no contradiction in supposing that one and the
same will is, in the appearance, that is, in its visible acts,
necessarily subject to the law of nature, and so far not free,
while yet, as belonging to a thing in itself, it is not subject
to that law, and is therefore free. My soul, viewed from the
latter standpoint, cannot indeed be known by means of speculative
reason (and still less through empirical observation);
and freedom as a property of a being to which I attribute effects
in the sensible world, is therefore also not knowable in any
such fashion. For I should then have to know such a being as
determined in its existence, and yet as not determined in time --
which is impossible, since I cannot support my concept by any
intuition. But though I cannot know, I can yet think freedom;
that is to say, the representation of it is at least not 
self-contradictory, provided due account be taken of our critical 
distinction between the two modes of representation, the sensible
and the intellectual, and of the resulting limitation of the pure
concepts of understanding and of the principles which flow
from them.
If we grant that morality necessarily presupposes freedom
(in the strictest sense) as a property of our will; if, that is to
say, we grant that it yields practical principles -- original 
principles, proper to our reason -- as a priori data of reason, and
that this would be absolutely impossible save on the 
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assumption of freedom; and if at the same time we grant that
speculative reason has proved that such freedom does not
allow of being thought, then the former supposition -- that
made on behalf of morality -- would have to give way to this
other contention, the opposite of which involves a palpable
contradiction. For since it is only on the assumption of freedom
that the negation of morality contains any contradiction,
freedom, and with it morality, would have to yield to the
mechanism of nature.
Morality does not, indeed, require that freedom should be
understood, but only that it should not contradict itself, and
so should at least allow of being thought, and that as thus
thought it should place no obstacle in the way of a free act
(viewed in another relation) likewise conforming to the mechanism
of nature. The doctrine of morality and the doctrine of
nature may each, therefore, make good its position. This,
however, is only possible in so far as criticism has previously
established our unavoidable ignorance of things in themselves,
and has limited all that we can theoretically know to mere
appearances.
This discussion as to the positive advantage of critical
principles of pure reason can be similarly developed in regard
to the concept of God and of the simple nature of our soul; but
for the sake of brevity such further discussion may be omitted.
[From what has already been said, it is evident that] even the
assumption--as made on behalf of the necessary practical 
employment of my reason -- of God, freedom, and immortality is
not permissible unless at the same time speculative reason be
deprived of its pretensions to transcendent insight. For in order
to arrive at such insight it must make use of principles which,
in fact, extend only to objects of possible experience, and
which, if also applied to what cannot be an object of experience,
always really change this into an appearance, thus rendering
all practical extension of pure reason impossible. I have therefore
found it necessary to deny knowledge, in order to make room
for faith. The dogmatism of metaphysics, that is, the preconception
that it is possible to make headway in metaphysics without
a previous criticism of pure reason, is the source of all that
unbelief, always very dogmatic, which wars against morality.
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Though it may not, then, be very difficult to leave to posterity
the bequest of a systematic metaphysic, constructed in
conformity with a critique of pure reason, yet such a gift is
not to be valued lightly. For not only will reason be enabled
to follow the secure path of a science, instead of, as hitherto,
groping at random, without circumspection or self-criticism;
our enquiring youth will also be in a position to spend
their time more profitably than in the ordinary dogmatism
by which they are so early and so greatly encouraged to
indulge in easy speculation about things of which they
understand nothing, and into which neither they nor anyone
else will ever have any insight -- encouraged, indeed, to
invent new ideas and opinions, while neglecting the study
of the better-established sciences. But, above all, there is
the inestimable benefit, that all objections to morality and
religion will be for ever silenced, and this in Socratic fashion,
namely, by the clearest proof of the ignorance of the objectors.
There has always existed in the world, and there will always
continue to exist, some kind of metaphysics, and with it the
dialectic that is natural to pure reason. It is therefore the first
and most important task of philosophy to deprive metaphysics,
once and for all, of its injurious influence, by 
attacking its errors at their very source.
Notwithstanding this important change in the field of the
sciences, and the loss of its fancied possessions which speculative
reason must suffer, general human interests remain in the
same privileged position as hitherto, and the advantages which
the world has hitherto derived from the teachings of pure
reason are in no way diminished. The loss affects only the
monopoly of the schools, in no respect the interests of humanity.
I appeal to the most rigid dogmatist, whether the proof of the
continued existence of our soul after death, derived from the
simplicity of substance, or of the freedom of the will as opposed
to a universal mechanism, arrived at through the subtle but
ineffectual distinctions between subjective and objective practical
necessity, or of the existence of God as deduced from the
concept of an ens realissimum (of the contingency of the
changeable and of the necessity of a prime mover), have ever,
upon passing out from the schools, succeeded in reaching the
public mind or in exercising the slightest influence on its 
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convictions? That has never been found to occur, and in view of
the unfitness of the common human understanding for such
subtle speculation, ought never to have been expected. Such
widely held convictions, so far as they rest on rational grounds,
are due to quite other considerations. The hope of a future life
has its source in that notable characteristic of our nature,
never to be capable of being satisfied by what is temporal (as
insufficient for the capacities of its whole destination); the
consciousness of freedom rests exclusively on the clear 
exhibition of duties, in opposition to all claims of the 
inclinations; the belief in a wise and great Author of the world is
generated solely by the glorious order, beauty, and providential
care everywhere displayed in nature. When the schools
have been brought to recognise that they can lay no claim
to higher and fuller insight in a matter of universal human
concern than that which is equally within the reach of the
great mass of men (ever to be held by us in the highest
esteem), and that, as Schools of philosophy, they should limit
themselves to the study of those universally comprehensible,
and, for moral purposes, sufficient grounds of proof, then
not only do these latter possessions remain undisturbed, but
through this very fact they acquire yet greater authority. The
change affects only the arrogant pretensions of the Schools,
which would fain be counted the sole authors and possessors
of such truths (as, indeed, they can justly claim to be in many
other branches of knowledge), reserving the key to themselves,
and communicating to the public their use only -- quod mecum
nescit, solus vult scire videri. At the same time due regard is
paid to the more moderate claims of the speculative philosopher.
He still remains the sole authority in regard to a science which
benefits the public without their knowing it, namely, the critique
of reason. That critique can never become popular, and indeed
there is no need that it should. For just as fine-spun arguments
in favour of useful truths make no appeal to the general mind,
so neither do the subtle objections that can be raised against
them. On the other hand, both inevitably present themselves
to everyone who rises to the height of speculation; and it is
therefore the duty of the Schools, by means of a thorough
investigation of the rights of speculative reason, once for all
to prevent the scandal which, sooner or later, is sure to
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break out even among the masses, as the result of the
disputes in which metaphysicians (and, as such, finally also
the clergy) inevitably become involved to the consequent
perversion of their teaching. Criticism alone can sever the
root of materialism, fatalism, atheism, free-thinking, fanaticism,
and superstition, which can be injurious universally; as
well as of idealism and scepticism, which are dangerous chiefly
to the Schools, and hardly allow of being handed on to the
public. If governments think proper to interfere with the
affairs of the learned, it would be more consistent with a wise
regard for science as well as for mankind, to favour the 
freedom of such criticism, by which alone the labours of reason
can be established on a firm basis, than to support the
ridiculous despotism of the Schools, which raise a loud cry of
public danger over the destruction of cobwebs to which the
public has never paid any attention, and the loss of which it
can therefore never feel.
This critique is not opposed to the dogmatic procedure of
reason in its pure knowledge, as science, for that must always
be dogmatic, that is, yield strict proof from sure principles
a priori. It is opposed only to dogmatism, that is, to the 
presumption that it is possible to make progress with pure 
knowledge, according to principles, from concepts alone (those that
are philosophical), as reason has long been in the habit of
doing; and that it is possible to do this without having first 
investigated in what way and by what right reason has come into
possession of these concepts. Dogmatism is thus the dogmatic
procedure of pure reason, without previous criticism of its own
powers. In withstanding dogmatism we must not allow ourselves
to give free rein to that loquacious shallowness, which assumes
for itself the name of popularity, nor yet to scepticism, which
makes short work with all metaphysics. On the contrary, such
criticism is the necessary preparation for a thoroughly grounded
metaphysics, which, as science, must necessarily be developed
dogmatically, according to the strictest demands of system,
in such manner as to satisfy not the general public but the 
requirements of the Schools. For that is a demand to which it
stands pledged, and which it may not neglect, namely, that it
carry out its work entirely a priori, to the complete satisfaction
of speculative reason. In the execution of the plan prescribed
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by the critique, that is, in the future system of metaphysics
we have therefore to follow the strict method of the celebrated
Wolff, the greatest of all the dogmatic philosophers. He was
the first to show by example (and by his example he awakened
that spirit of thoroughness which is not extinct in Germany)
how the secure progress of a science is to be attained only
through orderly establishment of principles, clear determination
of concepts, insistence upon strictness of proof, and avoidance
of venturesome, non-consecutive steps in our inferences.
He was thus peculiarly well fitted to raise metaphysics to the
dignity of a science, if only it had occurred to him to prepare
the ground beforehand by a critique of the organ, that is, of
pure reason itself. The blame for his having failed to do so
lies not so much with himself as with the dogmatic way
of thinking prevalent in his day, and with which the philosophers
of his time, and of all previous times, have no right
to reproach one another. Those who reject both the method
of Wolff and the procedure of a critique of pure reason can
have no other aim than to shake off the fetters of science
altogether, and thus to change work into play, certainty into
opinion, philosophy into philodoxy.
Now, as regards this second edition, I have, as is fitting,
endeavoured to profit by the opportunity, in order to remove,
wherever possible, difficulties and obscurity which, not 
perhaps without my fault, may have given rise to the many
misunderstandings into which even acute thinkers have fallen
in passing judgment upon my book. In the propositions themselves
and their proofs, and also in the form and completeness
of the [architectonic] plan, I have found nothing to alter. This
is due partly to the long examination to which I have subjected
them, before offering them to the public, partly to the
nature of the subject-matter with which we are dealing. For
pure speculative reason has a structure wherein everything
is an organ, the whole being for the sake of every part, and
every part for the sake of all the others, so that even the
smallest imperfection, be it a fault (error) or a deficiency, must
inevitably betray itself in use. This system will, as I hope,
maintain, throughout the future, this unchangeableness. It
is not self-conceit which justifies me in this confidence, but
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the evidence experimentally obtained through the parity of
the result, whether we proceed from the smallest elements
to the whole of pure reason or reverse-wise from the whole
(for this also is presented to reason through its final end
in the sphere of the practical) to each part. Any attempt to
change even the smallest part at once gives rise to 
contradictions, not merely in the system, but in human reason in
general. As to the mode of exposition, on the other hand,
much still remains to be done; and in this edition I have
sought to make improvements which should help in removing,
first, the misunderstanding in regard to the Aesthetic, especially
concerning the concept of time; secondly, the obscurity
of the deduction of the concepts of understanding; thirdly, a
supposed want of sufficient evidence in the proofs of the principles
of pure understanding; and finally, the false interpretation
placed upon the paralogisms charged against rational
psychology. Beyond this point, that is, beyond the end of the
first chapter of the Transcendental Dialectic, I have made no
changes in the mode of exposition. Time was too short to
P 035
allow of further changes;
P 034n
 The only addition, strictly so called, though one affecting the
method of proof only, is the new refutation of psychological idealism
(cf. below, p. 244), and a strict (also, as I believe, the only possible)
proof of the objective reality of outer intuition. However harmless
idealism may be considered in respect of the essential aims of metaphysics
(though, in fact, it is not thus harmless), it still remains a
scandal to philosophy and to human reason in general that the
existence of things outside us (from which we derive the whole
material of knowledge, even for our inner sense) must be accepted
merely on faith, and that if anyone thinks good to doubt their existence,
we are unable to counter his doubts by any satisfactory proof.
Since there is some obscurity in the expressions used in the proof,
from the third line to the sixth line, I beg to alter the passage as
follows: "But this permanent cannot be an intuition in me. For all
grounds of determination of my existence which are to be met with
in me are representations; and as representations themselves require a
permanent distinct from them, in relation to which their change,
and so my existence in the time wherein they change, may be 
determined. To this proof it will probably be objected, that I am 
immediately conscious only of that which is in me, that is, of my 
representation of outer things; and consequently that it must still remain
uncertain whether outside me there is anything corresponding to it,
or not.
P 035
 and besides, I have not found among
competent and impartial critics any misapprehension in regard
to the remaining sections. Though I shall not venture to name
these critics with the praise that is their due, the attention
which I have paid to their comments will easily be recognised
in the [new] passages [above mentioned]. These improvements
involve, however, a small loss, not to be prevented save by
making the book too voluminous, namely, that I have had
to omit or abridge certain passages, which, though not
indeed essential to the completeness of the whole, may yet
be missed by many readers as otherwise helpful. Only so
could I obtain space for what, as I hope, is now a more
intelligible exposition, which, though altering absolutely
nothing in the fundamentals of the propositions put forward
or even in their proofs, yet here and there departs
so far from the previous method of treatment, that mere 
interpolations could not be made to suffice. This loss, which is
small and can be remedied by consulting the first edition, will,
I hope, be compensated by the greater clearness of the new
P 036
text.
P 034n
But through inner experience I am conscious of my existence
P 035n
in time (consequently also of its determinability in time), and this is
more than to be conscious merely of my representation. It is identical
with the empirical consciousness of my existence, which is determinable
only through relation to something which, while bound up with
my existence, is outside me. This consciousness of my existence in
time is bound up in the way of identity with the consciousness of a
relation to something outside me, and it is therefore experience not
invention, sense not imagination, which inseparably connects this
outside something with my inner sense. For outer sense is already
in itself a relation of intuition to something actual outside me, and
the reality of outer sense, in its distinction from imagination, rests
simply on that which is here found to take place, namely, its being
inseparably bound up with inner experience, as the condition of its
possibility. If, with the intellectual consciousness of my existence, in
the representation 'I am', which accompanies all my judgments and
acts of understanding, I could at the same time connect a determination
of my existence through intellectual intuition, the consciousness
of a relation to something outside me would not be required.
But though that intellectual consciousness does indeed come first,
the inner intuition, in which my existence can alone be determined,
is sensible and is bound up with the condition of time. This 
determination, however, and therefore the inner experience itself, depends
P 036n
upon something permanent which is not in me, and consequently
can be only in something outside me, to which I must regard 
myself as standing in relation.
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I have observed, with pleasure and thankfulness, in
various published works -- alike in critical reviews and in 
independent treatises -- that the spirit of thoroughness is not
extinct in Germany, but has only been temporarily overshadowed
by the prevalence of a pretentiously free manner of
thinking; and that the thorny paths of the Critique have not
discouraged courageous and clear heads from setting themselves
to master my book -- a work which leads to a methodical,
and as such alone enduring, and therefore most necessary,
science of pure reason. To these worthy men, who so happily
combine thoroughness of insight with a talent for lucid 
exposition -- which I cannot regard myself as possessing -- I
leave the task of perfecting what, here and there, in its
exposition, is still somewhat defective; for in this regard
the danger is not that of being refuted, but of not being
P 037
understood.
P 036n
The reality of outer sense is thus necessarily
bound up with inner sense, if experience in general is to be
possible at all; that is, I am just as certainly conscious that there are
things outside me, which are in relation to my sense, as I am conscious
that I myself exist as determined in time. In order to determine
to which given intuitions objects outside me actually correspond,
and which therefore belong to outer sense (to which, and not
to the faculty of imagination, they are to be ascribed), we must in
each single case appeal to the rules according to which experience
in general, even inner experience, is distinguished from imagination
 -- the proposition that there is such a thing as outer experience being
always presupposed. This further remark may be added. The 
representation of something permanent in existence is not the same as
permanent representation. For though the representation of [something
permanent] may be very transitory and variable like all our
other representations, not excepting those of matter, it yet refers to
something permanent. This latter must therefore be an external
thing distinct from all my representations, and its existence must be
included in the determination of my own existence, constituting with
it but a single experience such as would not take place even inwardly
if it were not also at the same time, in part, outer. How this should
be possible we are as little capable of explaining further as we are of
accounting for our being able to think the abiding in time, the 
coexistence of which with the changing generates the concept of 
alteration. 
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From now on, though I cannot allow myself to
enter into controversy, I shall take careful note of all 
suggestions, be they from friends or from opponents, for use, in
accordance with this propaedeutic, in the further elaboration
of the system. In the course of these labours I have advanced
somewhat far in years (this month I reach my sixty-fourth
year), and I must be careful with my time if I am to succeed
in my proposed scheme of providing a metaphysic of nature
and of morals which will confirm the truth of my Critique in
the two fields, of speculative and of practical reason. The
clearing up of the obscurities in the present work -- they are
hardly to be avoided in a new enterprise -- and the defence
of it as a whole, I must therefore leave to those worthy men
who have made my teaching their own. A philosophical work
cannot be armed at all points, like a mathematical treatise,
and may therefore be open to objection in this or that respect,
while yet the structure of the system, taken in its unity, is not
in the least endangered. Few have the versatility of mind to
familiarise themselves with a new system; and owing to the
general distaste for all innovation, still fewer have the 
inclination to do so. If we take single passages, torn from their
contexts, and compare them with one another, apparent 
contradictions are not likely to be lacking, especially in a work
that is written with any freedom of expression. In the eyes of
those who rely on the judgment of others, such contradictions
have the effect of placing the work in an unfavourable
light; but they are easily resolved by those who have mastered
the idea of the whole. If a theory has in itself stability, the
stresses and strains which may at first have seemed very
threatening to it serve only, in the course of time, to smooth
away its inequalities; and if men of impartiality, insight, and
true popularity devote themselves to its exposition, it may also,
in a short time, secure for itself the necessary elegance of
statement.
Königsberg, April 1787.