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lines； there is no contradiction； for the conceptions of two
straight lines and of their junction contain no negation of a
figure。 The impossibility in such a case does not rest upon the
conception in itself； but upon the construction of it in space； that
is to say； upon the conditions of space and its determinations。 But
these have themselves objective reality； that is； they apply to
possible things； because they contain a priori the form of
experience in general。
And now we shall proceed to point out the extensive utility and
influence of this postulate of possibility。 When I represent to myself
a thing that is permanent； so that everything in it which changes
belongs merely to its state or condition； from such a conception alone
I never can cognize that such a thing is possible。 Or； if I
represent to myself something which is so constituted that； when it is
posited； something else follows always and infallibly； my thought
contains no self…contradiction； but whether such a property as
causality is to be found in any possible thing； my thought alone
affords no means of judging。 Finally； I can represent to myself
different things （substances） which are so constituted that the
state or condition of one causes a change in the state of the other；
and reciprocally； but whether such a relation is a property of
things cannot be perceived from these conceptions； which contain a
merely arbitrary synthesis。 Only from the fact； therefore； that
these conceptions express a priori the relations of perceptions in
every experience； do we know that they possess objective reality； that
is； transcendental truth； and that independent of experience； though
not independent of all relation to form of an experience in general
and its synthetical unity； in which alone objects can be empirically
cognized。
But when we fashion to ourselves new conceptions of substances；
forces； action； and reaction； from the material presented to us by
perception； without following the example of experience in their
connection； we create mere chimeras； of the possibility of which we
cannot discover any criterion； because we have not taken experience
for our instructress； though we have borrowed the conceptions from
her。 Such fictitious conceptions derive their character of possibility
not； like the categories； a priori； as conceptions on which all
experience depends； but only； a posteriori； as conceptions given by
means of experience itself； and their possibility must either be
cognized a posteriori and empirically； or it cannot be cognized at
all。 A substance which is permanently present in space； yet without
filling it （like that tertium quid between matter and the thinking
subject which some have tried to introduce into metaphysics）； or a
peculiar fundamental power of the mind of intuiting the future by
anticipation （instead of merely inferring from past and present
events）； or； finally； a power of the mind to place itself in munity
of thought with other men； however distant they may be… these are
conceptions the possibility of which has no ground to rest upon。 For
they are not based upon experience and its known laws； and； without
experience； they are a merely arbitrary conjunction of thoughts；
which； though containing no internal contradiction； has no claim to
objective reality； neither； consequently； to the possibility of such
an object as is thought in these conceptions。 As far as concerns
reality； it is self…evident that we cannot cogitate such a possibility
in concreto without the aid of experience； because reality is
concerned only with sensation； as the matter of experience； and not
with the form of thought； with which we can no doubt indulge in
shaping fancies。
But I pass by everything which derives its possibility from
reality in experience； and I purpose treating here merely of the
possibility of things by means of a priori conceptions。 I maintain；
then； that the possibility of things is not derived from such
conceptions per se； but only when considered as formal and objective
conditions of an experience in general。
It seems； indeed； as if the possibility of a triangle could be
cognized from the conception of it alone （which is certainly
independent of experience）； for we can certainly give to the
conception a corresponding object pletely a priori； that is to say；
we can construct it。 But as a triangle is only the form of an
object； it must remain a mere product of the imagination； and the
possibility of the existence of an object corresponding to it must
remain doubtful； unless we can discover some other ground； unless we
know that the figure can be cogitated under the conditions upon
which all objects of experience rest。 Now； the facts that space is a
formal condition a priori of external experience； that the formative
synthesis； by which we construct a triangle in imagination； is the
very same as that we employ in the apprehension of a phenomenon for
the purpose of making an empirical conception of it； are what alone
connect the notion of the possibility of such a thing； with the
conception of it。 In the same manner； the possibility of continuous
quantities； indeed of quantities in general； for the conceptions of
them are without exception synthetical； is never evident from the
conceptions in themselves； but only when they are considered as the
formal conditions of the determination of objects in experience。 And
where； indeed； should we look for objects to correspond to our
conceptions； if not in experience； by which alone objects are
presented to us？ It is； however； true that without antecedent
experience we can cognize and characterize the possibility of
things； relatively to the formal conditions； under which something
is determined in experience as an object； consequently； pletely a
priori。 But still this is possible only in relation to experience
and within its limits。
The postulate concerning the cognition of the reality of things
requires perception； consequently conscious sensation； not indeed
immediately； that is； of the object itself； whose existence is to be
cognized； but still that the object have some connection with a real
perception；