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； 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 plete； 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 paratively 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 e 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 already destroyed
in the transcendental aesthetic。 Problematical idealism； which makes
no such assertion； but only alleges our incapacity to prove the
existence of anything besides ourselves by means of immediate
experience； is a theory rational and evidencing a thorough and
philosophical mode of thinking； for it observes the rule not to form a
decisive judgement before sufficient proof be shown。 The desired proof
must therefore demonstrate that we have experience of external things；
and not mere fancies。 For this purpose； we must prove； that our
internal and； to Descartes； indubitable experience is itself
possible only under the previous assumption of external experience。
THEOREM。
The simple but empirically determined consciousness of
my own existence proves the existence of external
objects in space。
PROOF
I am conscious of my own existence as determined in time。 All
determination in regard to time presupposes the existence of something
permanent in perception。 But this permanent something cannot be
something in me； for the very reason that my existence in time is
itself determined by this permanent something。 It follows that the
perception of this permanent existence is possible only through a
thing without me and not through the mere representation of a thing
without me。 Consequently； the determination of my existence in time is
possible only through the existence of real things external to me。
Now； consciousness in time is necessarily connected with the
consciousness of the possibility of this determination in time。
Hence it follows that consciousness in time is necessarily connected
also with the existence of things without me； inasmuch as the
existence of these things is the condition of determination in time。
That is to say； the consciousness of my own existence is at the same
time an immediate consciousness of the existence of other things
without me。
Remark I。 The reader will observe； that in the foregoing proof the
game which idealism plays is retorted upon itself； and with more
justice。 It assumed that the only immediate experience is internal and
that from this we can only infer the existence of external things。
But； as always happens； when we reason from given effects to
determined causes； idealism bas reasoned with too much haste and
uncertainty； for it is quite possible that the cause of our
representations may lie in ourselves； and that we ascribe it falsely
to external things。 But our proof shows that external experience is
properly immediate；* that only by virtue of it… not； indeed； the
consciousness of our own existence； but certainly the determination of
our existence in time； that is； internal experience… is possible。 It
is true； that the representation 〃I am；〃 which is the expression of
the consciousness which can acpany all my thoughts； is that which
immediately includes the existence of a subject。 But in this
representation we cannot find any knowledge of the subject； and
therefore also no empirical knowledge； that is； experience。 For
experience contains； in addition to the thought of something existing；
intuition； and in this case it must be internal intuition； that is；
time； in relation to which the subject must be determined。 But the
existence of external things is absolutely requisite for this purpose；
so that it follows that internal experience is itself possible only
mediately and through external experience。
*The immediate consciousness of the existence of external things is；
in the preceding theorem； not presupposed； but proved； by the
possibility of this consciousness understood by us or not。 The
question as to the possibility of it would stand thus： 〃Have we an
internal sense； but no external sense； and is our belief in external
perception a mere delusion？〃 But it is evident that； in order merely
to fancy to ourselves anything as external； that is； to present it
to the sense in intuition we must already possess an external sense；
and must thereby distinguish immediately the mere receptivity of an
external intuition from the spontaneity which characterizes every
act of imagination。 For merely to imagine also an external sense；
would annihilate the faculty of intuition itself which is to be
determined by the imagination。
Remark II。 Now with this view all empirical use of our faculty of
cognition in the determination of time is in perfect accordance。 Its
truth is supported by the fact that it is possible to perceive a
determination of time only by means of a change in external
relations （motion） to the permanent in space （for example； we bee
aware of the sun's motion by observing the changes of his relation
to the objects of this earth）。 But this is not all。 We find that we
possess nothing p