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produce the conception of it； for example… 〃With a given line； to
describe a circle upon a plane； from a given point〃； and such a
proposition does not admit of proof； because the procedure； which it
requires； is exactly that by which alone it is possible to generate
the conception of such a figure。 With the same right； accordingly； can
we postulate the principles of modality； because they do not
augment* the conception of a thing but merely indicate the manner in
which it is connected with the faculty of cognition。
*When I think the reality of a thing； I do really think more than
the possibility； but not in the thing； for that can never contain more
in reality than was contained in its complete possibility。 But while
the notion of possibility is merely the notion of a position of
thing in relation to the understanding （its empirical use）； reality is
the conjunction of the thing with perception。
GENERAL REMARK ON THE SYSTEM OF PRINCIPLES。
It is very remarkable that we cannot perceive the possibility of a
thing from the category alone； but must always have an intuition； by
which to make evident the objective reality of the pure conception
of the understanding。 Take； for example； the categories of relation。
How （1） a thing can exist only as a subject； and not as a mere
determination of other things； that is； can be substance； or how
（2）； because something exists； some other thing must exist；
consequently how a thing can be a cause； or how （3）； when several
things exist； from the fact that one of these things exists； some
consequence to the others follows； and reciprocally； and in this way a
community of substances can be possible… are questions whose
solution cannot be obtained from mere conceptions。 The very same is
the case with the other categories； for example； how a thing can be of
the same sort with many others； that is； can be a quantity； and so on。
So long as we have not intuition we cannot know whether we do really
think an object by the categories； and where an object can anywhere be
found to cohere with them； and thus the truth is established； that the
categories are not in themselves cognitions； but mere forms of thought
for the construction of cognitions from given intuitions。 For the same
reason is it true that from categories alone no synthetical
proposition can be made。 For example： 〃In every existence there is
substance；〃 that is； something that can exist only as a subject and
not as mere predicate； or； 〃Everything is a quantity〃… to construct
propositions such as these； we require something to enable us to go
out beyond the given conception and connect another with it。 For the
same reason the attempt to prove a synthetical proposition by means of
mere conceptions； for example： 〃Everything that exists contingently
has a cause；〃 has never succeeded。 We could never get further than
proving that； without this relation to conceptions； we could not
conceive the existence of the contingent； that is； could not a
priori through the understanding cognize the existence of such a
thing； but it does not hence follow that this is also the condition of
the possibility of the thing itself that is said to be contingent。 If；
accordingly； we look back to our proof of the principle of
causality； we shall find that we were able to prove it as valid only
of objects of possible experience； and； indeed； only as itself the
principle of the possibility of experience； Consequently of the
cognition of an object given in empirical intuition； and not from mere
conceptions。 That； however； the proposition： 〃Everything that is
contingent must have a cause；〃 is evident to every one merely from
conceptions； is not to be denied。 But in this case the conception of
the contingent is cogitated as involving not the category of
modality （as that the non…existence of which can be conceive but
that of relation （as that which can exist only as the consequence of
something else）； and so it is really an identical proposition： 〃That
which can exist only as a consequence； has a cause。〃 In fact； when
we have to give examples of contingent existence； we always refer to
changes； and not merely to the possibility of conceiving the
opposite。* But change is an event； which； as such； is possible only
through a cause； and considered per se its non…existence is
therefore possible； and we become cognizant of its contingency from
the fact that it can exist only as the effect of a cause。 Hence； if
a thing is assumed to be contingent； it is an analytical proposition
to say； it has a cause。
*We can easily conceive the non…existence of matter； but the
ancients did not thence infer its contingency。 But even the
alternation of the existence and non…existence of a given state in a
thing； in which all change consists； by no means proves the
contingency of that state… the ground of proof being the reality of
its opposite。 For example； a body is in a state of rest after
motion； but we cannot infer the contingency of the motion from the
fact that the former is the opposite of the latter。 For this
opposite is merely a logical and not a real opposite to the other。
If we wish to demonstrate the contingency of the motion； what we ought
to prove is that； instead of the motion which took place in the
preceding point of time； it was possible for the body to have been
then in rest； not； that it is afterwards in rest； for in this case；
both opposites are perfectly consistent with each other。
But it is still more remarkable that； to understand the
possibility of things according to the categories and thus to
demonstrate the objective reality of the latter； we require not merely
intuitions； but external intuitions。 If； for example； we take the pure
conceptions of relation； we find that （1） for the purpose of
presenting to the conception of substance something permanent in
intuition corresponding thereto and thus of demonstrating the
objective reality of this conception； we require an intuition （of
matter） in space； because space alone is permanent and determines
things as such； while time； and with it all that is in the internal
sense； is in a state of continual flow； （2） in order to represent
change as the intuition corresponding to the conception of
causality； we require the representation of motion as change in space；
in fact； it is through it alone that changes； the possibility of which
no pure understanding can perceive； are capable of being intuited。
Change is the connection of determinations contradictorily opposed
to each other in the existence of one and the same thing。 Now； how
it is possible that out of a given state one quite opposite to it in
the same thing should follow； reason without an example can not only
not conceive； but cannot even make intelligible without intuition； and
this intuition is the motion of a point in space； the existence of
which in different spaces （as a consequence of opposite
determinations） alone makes the intuition of change possible。 For；
in order to make even internal change cognitable； we require to
represent time； as the form of the internal sense； figuratively by a
line； and the internal change by the drawing of that line （motion）；
and consequently are obliged to employ external intuition to be able
to represent the successive existence of ourselves in different
states。 The proper ground of this fact is that all change to be
perceived as change presupposes something permanent in intuition；
while in the internal sense no permanent intuition is to be found。
Lastly； the objective possibility of the category of community
cannot be conceived by mere reason； and consequently its objective
reality cannot be demonstrated without an intuition； and that external
in space。 For how can we conceive the possibility of community； that
is； when several substances exist； that some effect on the existence
of the one follows from the existence of the other； and
reciprocally； and therefore that； because something exists in the
latter； something else must exist in the former； which could not be
understood from its own existence alone？ For this is the very
essence of community… which is inconceivable as a property of things
which are perfectly isolated。 Hence； Leibnitz； in attributing to the
substances of the world… as cogitated by the understanding alone… a
community； required the mediating aid of a divinity； for； from their
existence； such a property seemed to him with justice inconceivable。
But we can very easily conceive the possibility of community （of
substances as phenomena） if we represent them to ourselves as in
space； consequently in external intuition。 For external intuition
contains in itself a priori formal external relations； as the
conditions of the possibility of the real relations of action and
reaction； and therefore of the possibility of community。 With the same
ease can it be demonstrated； that the possibility of things as