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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 community
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 completely 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； completely 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； in accordance with the analogies of experience； which
exhibit all kinds of real connection in experience。
From the mere conception of a thing it is impossible to conclude its
existence。 For； let the conception be ever so complete； and containing
a statement of all the determinations of the thing； the existence of
it has nothing to do with all this； but only with thew question
whether such a thing is given； so that the perception of it can in
every case precede the conception。 For the fact that the conception of
it precedes the perception； merely indicates the possibility of its
existence； it is perception which presents matter to the conception；
that is the sole criterion of reality。 Prior to the perception of
the thing； however； and therefore comparatively a priori； we are
able to cognize its existence； provided it stands in connection with
some perceptions according to the principles of the empirical
conjunction of these； that is； in conformity with the analogies of
perception。 For； in this case； the existence of the supposed thing
is connected with our perception in a possible experience； and we
are able； with the guidance of these analogies； to reason in the
series of possible perceptions from a thing which we do really
perceive to the thing we do not perceive。 Thus； we cognize the
existence of a magnetic matter penetrating all bodies from the
perception of the attraction of the steel…filings by the magnet；
although the constitution of our organs renders an immediate
perception of this matter impossible for us。 For； according to the
laws of sensibility and the connected context of our perceptions； we
should in an experience come also on an immediate empirical
intuition of this matter； if our senses were more acute… but this
obtuseness has no influence upon and cannot alter the form of possible
experience in general。 Our knowledge of the existence of things
reaches as far as our perceptions； and what may be inferred from
them according to empirical laws； extend。 If we do not set out from
experience； or do not proceed according to the laws of the empirical
connection of phenomena； our pretensions to discover the existence
of a thing which we do not immediately perceive are vain。 Idealism；
however； brings forward powerful objections to these rules for proving
existence mediately。 This is； therefore； the proper place for its
refutation。
REFUTATION OF IDEALISM。
Idealism… I mean material idealism… is the theory which declares the
existence of objects in space without us to be either （） doubtful
and indemonstrable； or （2） false and impossible。 The first is the
problematical idealism of Descartes； who admits the undoubted
certainty of only one empirical assertion （assertio）； to wit； 〃I
am。〃 The second is the dogmatical idealism of Berkeley； who
maintains that space； together with all the objects of which it is the
inseparable condition； is a thing which is in itself impossible； and
that consequently the objects in space are mere products of the
imagination。 The dogmatical theory of idealism is unavoidable； if we
regard space as a property of things in themselves； for in that case
it is； with all to which it serves as condition； a nonentity。 But
the foundation for this kind of idealism we have alrea