sense is necessarily connected with that of the internal； in order
to the possibility of experience in general； that is； I am just as
certainly conscious that there are things external to me related to my
sense as I am that I myself exist as determined in time。 But in
order to ascertain to what given intuitions objects； external me；
really correspond； in other words； what intuitions belong to the
external sense and not to imagination； I must have recourse； in
every particular case； to those rules according to which experience in
general （even internal experience） is distinguished from
imagination； and which are always based on the proposition that
there really is an external experience。 We may add the remark that the
representation of something permanent in existence； is not the same
thing as the permanent representation； for a representation may be
very variable and changing… as all our representations； even that of
matter； are… and yet refer to something permanent； which must；
therefore； be distinct from all my representations and external to me；
the existence of which is necessarily included in the determination of
my own existence； and with it constitutes one experience… an
experience which would not even be possible internally； if it were not
also at the same time； in part； external。 To the question How？ we
are no more able to reply； than we are； in general； to think the
stationary in time； the coexistence of which with the variable；
produces the conception of change。
In attempting to render the exposition of my views as intelligible
as possible； I have been pelled to leave out or abridge various
passages which were not essential to the pleteness of the work； but
which many readers might consider useful in other respects； and
might be unwilling to miss。 This trifling loss； which could not be
avoided without swelling the book beyond due limits； may be
supplied； at the pleasure of the reader； by a parison with the
first edition； and will； I hope； be more than pensated for by the
greater clearness of the exposition as it now stands。
I have observed； with pleasure and thankfulness； in the pages of
various reviews and treatises； that the spirit of profound and
thorough investigation is not extinct in Germany； though it may have
been overborne and silenced for a time by the fashionable tone of a
licence in thinking； which gives itself the airs of genius； and that
the difficulties which beset the paths of criticism have not prevented
energetic and acute thinkers from making themselves masters of the
science of pure reason to which these paths conduct… a science which
is not popular； but scholastic in its character； and which alone can
hope for a lasting existence or possess an abiding value。 To these
deserving men； who so happily bine profundity of view with a talent
for lucid exposition… a talent which I myself am not conscious of
possessing… I leave the task of removing any obscurity which may still
adhere to the statement of my doctrines。 For； in this case； the danger
is not that of being refuted； but of being misunderstood。 For my own
part； I must henceforward abstain from controversy； although I shall
carefully attend to all suggestions； whether from friends or
adversaries； which may be of use in the future elaboration of the
system of this propaedeutic。 As； during these labours； I have advanced
pretty far in years this month I reach my sixty…fourth year… it will
be necessary for me to economize time； if I am to carry out my plan of
elaborating the metaphysics of nature as well as of morals； in
confirmation of the correctness of the principles established in
this Critique of Pure Reason； both speculative and practical； and I
must； therefore； leave the task of clearing up the obscurities of
the present work… inevitable； perhaps； at the outset… as well as；
the defence of the whole； to those deserving men； who have made my
system their own。 A philosophical system cannot e forward armed
at all points like a mathematical treatise； and hence it may be
quite possible to take objection to particular passages； while the
organic structure of the system； considered as a unity； has no
danger to apprehend。 But few possess the ability； and still fewer
the inclination； to take a prehensive view of a new system。 By
confining the view to particular passages； taking these out of their
connection and paring them with one another； it is easy to pick out
apparent contradictions； especially in a work written with any freedom
of style。 These contradictions place the work in an unfavourable light
in the eyes of those who rely on the judgement of others； but are
easily reconciled by those who have mastered the idea of the whole。 If
a theory possesses stability in itself； the action and reaction
which seemed at first to threaten its existence serve only； in the
course of time； to smooth down any superficial roughness or
inequality； and… if men of insight； impartiality； and truly popular
gifts； turn their attention to it… to secure to it； in a short time；
the requisite elegance also。
Konigsberg； April 1787。
INTRODUCTION
INTRODUCTION。
I。 Of the difference between Pure and Empirical Knowledge
That all our knowledge begins with experience there can be no doubt。
For how is it possible that the faculty of cognition should be
awakened into exercise otherwise than by means of objects which affect
our senses； and partly of themselves produce representations； partly
rouse our powers of understanding into activity； to pare to
connect； or to separate these； and so to convert the raw material of
our sensuous impressions into a knowledge of objects； which is
called experience？ In respect of time； therefore； no knowledge of ours
is antecedent to experience； but begins with it。
But； though all our knowledge begins with experience； it by no means
follows that all arises out of experience。 For； on the contrary； it is
quite possible that our empirical knowledge is a pound of that
which we receive through impressions； and that which the faculty of
cognition supplies from itself （sensuous impressions giving merely the
occasion）； an addition which we cannot distinguish from the original
element given by sense； till long practice has made us attentive to；
and skilful in separating it。 It is； therefore； a question which
requires close investigation； and not to be answered at first sight；
whether there exists a knowledge altogether independent of experience；
and even of all sensuous impressions？ Knowledge of this kind is called
a priori； in contradistinction to empirical knowledge； which has its
sources a posteriori； that is； in experience。
But the expression； 〃a priori；〃 is not as yet definite enough
adequately to indicate the whole meaning of the question above
started。 For； in speaking of knowledge which has its sources in
experience； we are wont to say； that this or that may be known a
priori； because we do not derive this knowledge immediately from
experience； but from a general rule； which； however； we have itself
borrowed from experience。 Thus； if a man undermined his house； we say；
〃he might know a priori that it would have fallen；〃 that is； he needed
not to have waited for the experience that it did actually fall。 But
still； a priori； he could not know even this much。 For； that bodies
are heavy； and； consequently； that they fall when their supports are
taken away； must have been known to him previously； by means of
experience。
By the term 〃knowledge a priori；〃 therefore； we shall in the
sequel understand； not such as is independent of this or that kind
of experience； but such as is absolutely so of all experience。 Opposed
to this is empirical knowledge； or that which is possible only a
posteriori； that is； through experience。 Knowledge a priori is
either pure or impure。 Pure knowledge a priori is that with which no
empirical element is mixed up。 For example； the proposition； 〃Every
change has a cause；〃 is a proposition a priori； but impure； because
change is a conception which can only be derived from experience。
II。 The Human Intellect； even in an Unphilosophical State；
is in Possession of Certain Cognitions 〃a priori〃。
The question now is as to a criterion； by which we may securely
distinguish a pure from an empirical cognition。 Experience no doubt
teaches us that this or that object is constituted in such and such
a manner； but not that it could not possibly exist otherwise。 Now；
in the first place； if we have a proposition which contains the idea
of necessity in its very conception； it is a if； moreover； it is not
derived from any other proposition； unless from one equally
involving the idea of necessity； it is absolutely priori。 Secondly； an
empirical judgement never exhibits strict and absolute； but only
assumed and parative universality （by induction）； therefore； the
most we can say is… so far as we have hitherto observed； there is no
exception to this or that rule。 If； on the other hand； a judgement
carries with it strict and absolute universality； that is； admits of
no possible exception； it is not derived from experience； but is valid
absolutely a priori。
Empirical universality is； therefore； only an arbitrary extension of
validity； from that which may be predicated of a proposition valid
in most cases； to that which is asserted of a proposition which
holds good in all； as； for example； in the affirmation； 〃All bodies
are heavy。〃 When； on the contrary； strict universality characterizes a
judgement； it necessarily indicates another peculiar source of
knowledge； namely； a faculty of cognition a priori。 Necessity and
strict universality； therefore； are infallible tests for
distinguishing pure from empirical knowledge； and are inseparably
connected with each other。 But as in the use of these criteria the
empirical limitation is sometimes more easily detected than the
contingency of the judgement； or the unlimited universality which we
attach to a judgement is often a more convincing proof than its
necessity； it may be advisable to use the criteria separately； each
being by itself infallible。
Now； that in the sphere of human cognition we have judgements
which