Principle of Succession in Time, in accordance with the
Law of Causality
All alterations take place in conformity with the law of the
connection of cause and effect.
(The preceeding principle has shown that all appearances
of succession in time are one and all only alterations, that is
a successive being and not-being of the determinations of
substance which abides; and therefore that the being of
substance as following on its not-being, or its not-being as
following upon its being cannot be admitted -- in other words, B233
that there is no coming into being or passing away of substance
itself. Still otherwise expressed the principle is, that
all change (succession) of appearances is merely alteration.
Coming into being and passing away of substance are not
alterations of it, since the concept of alteration presupposes
one and the same subject as existing with two opposite
determinations, and therefore as abiding. With this preliminary
reminder, we pass to the proof. )
I perceive that appearances follow one another, that is, that
there is a state of things at one time the opposite of which was
in the preceding time. Thus I am really connecting two
perceptions in time. Now connection is not the work of mere sense
and intuition, but is here the product of a synthetic faculty
of imagination, which determines inner sense in respect of the
But imagination can connect these two states
in two ways, so that either the one or the other precedes in
time. For time cannot be perceived in itself, and what precedes
and what follows cannot, therefore, by relation to it, be
empirically determined in the object. I am conscious only that
my imagination sets the one state before and the other after,
not that the one state precedes the other in the object. In other
words, the objective relation of appearances that follow upon B234
one another is not to be determined through mere perception.
In order that this relation be known as determined, the relation
between the two states must be so thought that it is thereby
determined as necessary which of them must be placed
before, and which of them after, and that they cannot be
placed in the reverse relation. But the concept which carries
with it a necessity of synthetic unity can only be a pure
concept that lies in the understanding, not in perception;
and in this case it is the concept of the relation of cause
and effect, the former of which determines the latter in time,
as its consequence -- not as in a sequence that may occur
solely in the imagination (or that may not be perceived at
all). Experience itself -- in other words, empirical knowledge
of appearances -- is thus possible only in so far as we subject
the succession of appearances, and therefore all alteration,
to the law of causality; and, as likewise follows, the appearances,
as objects of experience, are themselves possible only
in conformity with the law.
The apprehension of the manifold of appearance is always
successive. The representations of the parts follow upon one
another. Whether they also follow one another in the object
is a point which calls for further reflection, and which is not
decided by the above statement. Everything, every representation
even, in so far as we are conscious of it, may be
entitled object. But it is a question for deeper enquiry what B235
the word 'object' ought to signify in respect of appearances A190
when these are viewed not in so far as they are (as representations)
objects, but only in so far as they stand for an object. The
appearances, in so far as they are objects of consciousness
simply in virtue of being representations, are not in any way
distinct from their apprehension, that is, from their reception
in the synthesis of imagination; and we must therefore
agree that the manifold of appearances is always generated in
the mind successively. Now if appearances were things in themselves,
then since we have to deal solely with our representations,
we could never determine from the succession of the representations
how their manifold may be connected in the object. How
things may be in themselves, apart from the representations
through which they affect us, is entirely outside our sphere of
knowledge. In spite, however, of the fact that the appearances
are not things in themselves, and yet are what alone can be
given to us to know, in spite also of the fact that their
representation in apprehension is always successive, I have to show
what sort of a connection in time belongs to the manifold
in the appearances themselves. For instance, the apprehension
of the manifold in the appearance of a house which
stands before me is successive. The question then arises,
whether the manifold of the house is also in itself
successive. This, however, is what no one will grant. Now
immediately I unfold the transcendental meaning of my concepts B236
of an object, I realise that the house is not a thing in itself,
but only an appearance, that is, a representation, the  A191
transcendental object of which is unknown. What, then, am I to
understand by the question: how the manifold may be connected
in the appearance itself, which yet is nothing in itself?
That which lies in the successive apprehension is here viewed
as representation, while the appearance which is given to
me, notwithstanding that it is nothing but the sum of these
representations, is viewed as their object; and my concept,
which I derive from the representations of apprehension, has
to agree with it. Since truth consists in the agreement of
knowledge with the object, it will at once be seen that we can
here enquire only regarding the formal conditions of empirical
truth, and that appearance, in contradistinction to the
representations of apprehension, can be represented as an object
distinct from them only if it stands under a rule which
distinguishes it from every other apprehension and necessitates
some one particular mode of connection of the manifold. The
object is that in the appearance which contains the condition
of this necessary rule of apprehension.
Let us now proceed to our problem. That something
happens, i.e. that something, or some state which did not
previously exist, comes to be, cannot be perceived unless it is B237
preceded by an appearance which does not contain in itself this
state. For an event which should follow upon an empty time, A192
that is, a coming to be preceded by no state of things, is as
little capable of being apprehended as empty time itself. Every
apprehension of an event is therefore a perception that
follows upon another perception. But since, as I have above
illustrated by reference to the appearance of a house, this
likewise happens in all synthesis of apprehension, the apprehension
of an event is not yet thereby distinguished from other
apprehensions. But, as I also note, in an appearance which
contains a happening (the preceding state of the perception
we may entitle A, and the succeeding B) B can be
apprehended only as following upon A; the perception A
cannot follow upon B but only precede it. For instance, I
see a ship move down stream. My perception of its lower
position follows upon the perception of its position higher
up in the stream, and it is impossible that in the
apprehension of this appearance the ship should first be
perceived lower down in the stream and afterwards higher up.
The order in which the perceptions succeed one another in
apprehension is in this instance determined, and to this order
apprehension is bound down. In the previous example of a
house my perceptions could begin with the apprehension of
the roof and end with the basement, or could begin from below B238
and end above; and I could similarly apprehend the manifold
of the empirical intuition either from right to left or from left
to right. In the series of these perceptions there was thus no A193
determinate order specifying at what point I must begin in
order to connect the manifold empirically. But in the perception
of an event there is always a rule that makes the order in
which the perceptions (in the apprehension of this appearance)
follow upon one another a necessary order.
In this case, therefore, we must derive the subjective
succession of apprehension from the objective succession of
appearances. Otherwise the order of apprehension is entirely
undetermined, and does not distinguish one appearance from
another. Since the subjective succession by itself is altogether
arbitrary, it does not prove anything as to the manner in
which the manifold is connected in the object. The objective
succession will therefore consist in that order of the manifold
of appearance according to which, in conformity with a
rule, the apprehension of that which happens follows upon
the apprehension of that which precedes. Thus only can I be
justified in asserting, not merely of my apprehension, but of
appearance itself, that a succession is to be met with in it.
This is only another way of saying that I cannot arrange the
apprehension otherwise than in this very succession.
In conformity with such a rule there must lie in that which
precedes an event the condition of a rule according to which B239
this event invariably and necessarily follows. I cannot reverse
this order, proceeding back from the event to determine A194
through apprehension that which precedes. For appearance
never goes back from the succeeding to the preceding point
of time, though it does indeed stand in relation to some
preceding point of time. The advance, on the other hand, from
a given time to the determinate time that follows is a necessary
advance. Therefore, since there certainly is something
that follows [i.e. that is apprehended as following], I must refer
it necessarily to something else which precedes it and upon
which it follows in conformity with a rule, that is, of necessity.
The event, as the conditioned, thus affords reliable evidence of
some condition, and this condition is what determines the event.
Let us suppose that there is nothing antecedent to an event,
upon which it must follow according to rule. All succession of
perception would then be only in the apprehension, that is,
would be merely subjective, and would never enable us to
determine objectively which perceptions are those that really
precede and which are those that follow. We should then
have only a play of representations, relating to no object;
that is to say, it would not be possible through our perception
to distinguish one appearance from another as regards
relations of time. For the succession in our apprehension
would always be one and the same, and there would be nothing
in the appearance which so determines it that a certain  B240
sequence is rendered objectively necessary. I could not then
assert that two states follow upon one another in the [field of] A195
appearance, but only that one apprehension follows upon the
other. That is something merely subjective, determining no
object; and may not, therefore, be regarded as knowledge of
any object, not even of an object in the [field of] appearance.
If, then, we experience that something happens, we in
so doing always presuppose that something precedes it, on
which it follows according to a rule. Otherwise I should not
say of the object that it follows. For mere succession in my
apprehension, if there be no rule determining the succession
in relation to something that precedes, does not justify me
in assuming any succession in the object. I render my subjective
synthesis of apprehension objective only by reference
to a rule in accordance with which the appearances in their
succession, that is, as they happen, are determined by the
preceding state. The experience of an event [i.e. of anything as
happening] is itself possible only on this assumption.
This may seem to contradict all that has hitherto been
taught in regard to the procedure of our understanding. The
accepted view is that only through the perception and comparison
of events repeatedly following in a uniform manner upon
preceding appearances are we enabled to discover a rule
according to which certain events always follow upon certain B241
appearances, and that this is the way in which we are first led
to construct for ourselves the concept of cause. Now the  A196
concept, if thus formed, would be merely empirical, and the rule
which it supplies, that everything which happens has a cause,
would be as contingent as the experience upon which it is
based. Since the universality and necessity of the rule would
not be grounded a priori, but only on induction, they would
be merely fictitious and without genuinely universal validity.
It is with these, as with other pure a priori representations --
for instance, space and time. We can extract clear concepts
of them from experience, only because we have put them into
experience, and because experience is thus itself brought
about only by their means. Certainly, the logical clearness of
this representation of a rule determining the series of events is
possible only after we have employed it in experience. Nevertheless,
recognition of the rule, as a condition of the synthetic
unity of appearances in time, has been the ground of
experience itself, and has therefore preceded it a priori.
We have, then, to show, in the case under consideration,
that we never, even in experience, ascribe succession (that is,
the happening of some event which previously did not exist)
to the object, and so distinguish it from subjective sequence
in our apprehension, except when there is an underlying rule B242
which compels us to observe this order of perceptions rather
than any other; nay, that this compulsion is really what first A197
makes possible the representation of a succession in the object.
We have representations in us, and can become conscious
of them. But however far this consciousness may extend, and
however careful and accurate it may be, they still remain mere
representations, that is, inner determinations of our mind in
this or that relation of time. How, then, does it come about
that we posit an object for these representations, and so, in
addition to their subjective reality, as modifications, ascribe
to them some mysterious kind of objective reality. Objective
meaning cannot consist in the relation to another representation
(of that which we desire to entitle object), for in that case
the question again arises, how this latter representation goes
out beyond itself, acquiring objective meaning in addition to
the subjective meaning which belongs to it as determination
of the mental state. If we enquire what new character relation
to an object confers upon our representations, what dignity they
thereby acquire, we find that it results only in subjecting the
representations to a rule, and so in necessitating us to connect
them in some one specific manner; and conversely, that only
in so far as our representations are necessitated in a certain B243
order as regards their time-relations do they acquire objective
 In the synthesis of appearances the manifold of representations A198
is always successive. Now no object is hereby represented,
since through this succession, which is common to all
apprehensions, nothing is distinguished from anything else. But
immediately I perceive or assume that in this succession there
is a relation to the preceding state, from which the representation
follows in conformity with a rule, I represent something
as an event, as something that happens; that is to say, I
apprehend an object to which I must ascribe a certain determinate
position in time -- a position which, in view of the preceding
state, cannot be otherwise assigned. When, therefore, I perceive
that something happens, this representation first of all
contains [the consciousness] that there is something preceding,
because only by reference to what precedes does the appearance
acquire its time-relation, namely, that of existing after a
preceding time in which it itself was not. But it can acquire
this determinate position in this relation of time only in so far
as something is presupposed in the preceding state upon which
it follows invariably, that is, in accordance with a rule. From
this there results a twofold consequence. In the first place, I
cannot reverse the series, placing that which happens prior to
that upon which it follows. And secondly, if the state which
precedes is posited, this determinate event follows inevitably B244
and necessarily. The situation, then, is this: there is an order
in our representations in which the present, so far as it has
come to be, refers us to some preceding state as a correlate of A199
the event which is given; and though this correlate is, indeed,
indeterminate, it none the less stands in a determining relation
to the event as its consequence, connecting the event in
necessary relation with itself in the time-series.
If, then, it is a necessary law of our sensibility, and therefore
a formal condition of all perceptions, that the preceding
time necessarily determines the succeeding (since I cannot
advance to the succeeding time save through the preceding), it is
also an indispensable law of empirical representation of the
time-series that the appearances of past time determine all
existences in the succeeding time, and that these latter, as
events, can take place only in so far as the appearances of past
time determine their existence in time, that is, determine them
according to a rule. For only in appearances can we empirically
apprehend this continuity in the connection of times.
Understanding is required for all experience and for its
possibility. Its primary contribution does not consist in making
the representation of objects distinct, but in making the
representation of an object possible at all. This it does by carrying
the time-order over into the appearances and their existence. B245
For to each of them, [viewed] as [a] consequent, it assigns,
through relation to the preceding appearances, a position
determined a priori in time. Otherwise, they would not accord
with time itself, which [in] a priori [fashion] determines the A200
position of all its parts. Now since absolute time is not an
object of perception, this determination of position cannot be
derived from the relation of appearances to it. On the contrary,
the appearances must determine for one another their position
in time, and make their time-order a necessary order. In other
words, that which follows or happens must follow in conformity
with a universal rule upon that which was contained in
the preceding state. A series of appearances thus arises which,
with the aid of the understanding, produces and makes necessary
the same order and continuous connection in the series
of possible perceptions as is met with a priori in time -- the
form of inner intuition wherein all perceptions must have a
That something happens is, therefore, a perception which
belongs to a possible experience. This experience becomes
actual when I regard the appearance as determined in its
position in time, and therefore as an object that can always be
found in the connection of perceptions in accordance with a
rule. This rule, by which we determine something according to B246
succession of time, is, that the condition under which an event
invariably and necessarily follows is to be found in what precedes
the event. The principle of sufficient reason is thus the A201
ground of possible experience, that is, of objective knowledge
of appearances in respect of their relation in the succession of
The proof of this principle rests on the following considerations.
All empirical knowledge involves the synthesis of the
manifold by the imagination. This synthesis is always successive,
that is, the representations in it are always sequent upon
one another. In the imagination this sequence is not in any
way determined in its order, as to what must precede and
what must follow, and the series of sequent representations
can indifferently be taken either in backward or in forward
order. But if this synthesis is a synthesis of apprehension of
the manifold of a given appearance, the order is determined
in the object, or, to speak more correctly, is an order of
successive synthesis that determines an object. In accordance
with this order something must necessarily precede, and when
this antecedent is posited, something else must necessarily
follow. If, then, my perception is to contain knowledge of an
event, of something as actually happening, it must be an
empirical judgment in which we think the sequence as
determined; that is, it presupposes another appearance in time, B247
upon which it follows necessarily, according to a rule. Were
it not so, were I to posit the antecedent and the event were
not to follow necessarily thereupon, I should have to regard
the succession as a merely subjective play of my fancy; and if
I still represented it to myself as something objective, I should A202
have to call it a mere dream. Thus the relation of appearances
(as possible perceptions) according to which the subsequent
event, that which happens, is, as to its existence, necessarily
determined in time by something preceding in conformity
with a rule -- in other words, the relation of cause to effect -- is
the condition of the objective validity of our empirical judgments,
in respect of the series of perceptions, and so of their
empirical truth; that is to say, it is the condition of experience.
The principle of the causal relation in the sequence of appearances
is therefore also valid of all objects of experience ([in
so far as they are] under the conditions of succession), as
being itself the ground of the possibility of such experience.
At this point a difficulty arises with which we must at
once deal. The principle of the causal connection among
appearances is limited in our formula to their serial succession,
whereas it applies also to their coexistence, when cause and
effect are simultaneous. For instance, a room is warm while
the outer air is cool. I look around for the cause, and find a B248
heated stove. Now the stove, as cause, is simultaneous with its
effect, the heat of the room. Here there is no serial succession
in time between cause and effect. They are simultaneous, and
yet the law is valid. The great majority of efficient natural A203
causes are simultaneous with their effects, and the sequence
in time of the latter is due only to the fact that the cause
cannot achieve its complete effect in one moment. But in
the moment in which the effect first comes to be, it is
invariably simultaneous with the causality of its cause. If the
 cause should have ceased to exist a moment before, the effect
would never have come to be. Now we must not fail to note
that it is the order of time, not the lapse of time, with which
we have to reckon; the relation remains even if no time has
elapsed. The time between the causality of the cause and its
immediate effect may be [a] vanishing [quantity], and they
may thus be simultaneous; but the relation of the one to the
other will always still remain determinable in time. If I view
as a cause a ball which impresses a hollow as it lies on a
stuffed cushion, the cause is simultaneous with the effect. But
I still distinguish the two through the time-relation of their
dynamical connection. For if I lay the ball on the cushion,
a hollow follows upon the previous flat smooth shape; but
if (for any reason) there previously exists a hollow in the  B249
cushion, a leaden ball does not follow upon it.
The sequence in time is thus the sole empirical criterion
of an effect in its relation to the causality of the cause which
precedes it. A glass [filled with water] is the cause of the rising A204
of the water above its horizontal surface, although both appearances
are simultaneous. For immediately I draw off
water from a larger vessel into the glass, something follows,
namely the alteration from the horizontal position which the
water then had to the concave form which it assumes in the
Causality leads to the concept of action, this in turn to the
concept of force, and thereby to the concept of substance.
As my critical scheme, which is concerned solely with the
sources of synthetic a priori knowledge, must not be
complicated through the introduction of analyses which aim only
at the clarification, not at the extension, of concepts, I leave
detailed exposition of my concepts to a future
system of pure reason. Such an analysis has already, indeed, been developed
in considerable detail in the text-books. But I must
not leave unconsidered the empirical criterion of a substance,
in so far as substance appears to manifest itself not through
permanence of appearance, but more adequately and easily
through action.
Wherever there is action -- and therefore activity and force B250
 -- there is also substance, and it is in substance alone that the
seat of this fruitful source of appearances must be sought.
This is, so far, well said; but when we seek to explain what
is to be understood by substance, and in so doing are careful
to avoid the fallacy of reasoning in a circle, the discovery of
an answer is no easy task. How are we to conclude directly A205
from the action to the permanence of that which acts? For
that is an essential and quite peculiar characteristic of
substance (as phenomenon). But while according to the usual
procedure, which deals with concepts in purely analytic fashion, this
question would be completely insoluble, it presents no such
difficulty from the standpoint which we have been formulating.
Action signifies the relation of the subject of causality to its
effect. Since, now, every effect consists in that which happens,
and so in the transitory, which signifies time in its character
of succession, its ultimate subject, as the substratum of
everything that changes, is the permanent, that is, substance.
For according to the principle of causality actions are always
the first ground of all change of appearances, and cannot
therefore be found in a subject which itself changes, because
in that case other actions and another subject would be
required to determine this change. For this reason action is a
sufficient empirical criterion to establish the substantiality
of a subject, without my requiring first to go in quest of its B251
permanence through the comparison of perceptions. Besides,
by such method (of comparison) we could not achieve the
completeness required for the magnitude and strict universality
of the concept. That the first subject of the causality
of all coming to be and ceasing to be cannot itself, in the field
of appearances, come to be and cease to be, is an assured A206
conclusion which leads to [the concept of] empirical necessity
and permanence in existence, and so to the concept of a
substance as appearance.
When something happens, the mere coming to be, apart
from all question of what it is that has come to be, is already in
itself a matter for enquiry. The transition from the not-being
of a state to this state, even supposing that this state [as it
occurs] in the [field of] appearance exhibited no quality, of
itself demands investigation. This coming to be, as was shown
above in the First Analogy, does not concern substance, which
does not come to be out of nothing. For if coming to be out of
nothing is regarded as effect of a foreign cause, it has to be
entitled creation, and that cannot be admitted as an event
among appearances since its mere possibility would destroy
the unity of experience. On the other hand, when I view all
things not as phenomena but as things in themselves, and
as objects of the mere understanding, then despite their B252
being substances they can be regarded, in respect of their
existence, as depending upon a foreign cause. But our
terms would then carry with them quite other meanings,
and would not apply to appearances as possible objects of
How anything can be altered, and how it should be possible
that upon one state in a given moment an opposite state may A207
follow in the next moment -- of this we have not, a priori, the
least conception. For that we require knowledge of actual
forces, which can only be given empirically, as, for instance,
of the moving forces, or what amounts to the same thing, of
certain successive appearances, as motions, which indicate [the
presence of] such forces. But apart from all question of what
the content of the alteration, that is, what the state which
is altered, may be, the form of every alteration, the condition
under which, as a coming to be of another state, it can alone
take place, and so the succession of the states themselves (the
happening), can still be considered a priori according to the
law of causality and the conditions of time.
 If a substance passes from one state, a, to another, b, the B253
point of time of the second is distinct from that of the first, and follows upon
Similarly, the second state as reality in the
[field of] appearance differs from the first wherein it did not
exist, as b from zero. That is to say, even if the state b
differed from the state a only in magnitude, the alteration
would be a coming to be of b - a, which did not exist in the A208
previous state, and in respect of which it = 0.
The question therefore arises how a thing passes from one
state = a to another = b. Between two instants there is
always a time, and between any two states in the two instants
there is always a difference which has magnitude. For all parts
of appearances are always themselves magnitudes. All transition
from one state to another therefore occurs in a time which
is contained between two instants, of which the first determines
the state from which the thing arises, and the second
that into which it passes. Both instants, then, are limits of the
time of a change, and so of the intermediate state between the
two states, and therefore as such form part of the total alteration.
Now every alteration has a cause which evinces its causality in
the whole time in which the alteration takes place. This cause,
therefore, does not engender the alteration suddenly, that is, at
once or in one instant, but in a time; so that, as the time  B254
increases from the initial instant a to its completion in b, the
magnitude of the reality (b - a) is in like manner generated
through all smaller degrees which are contained between the
first and the last. All alteration is thus only possible through a
continuous action of the causality which, so far as it is uniform,
is entitled a moment. The alteration does not consist of these
moments, but is generated by them as their effect. A209
That is the law of the continuity of all alteration. Its ground
is this: that neither time nor appearance in time consists of parts
which are the smallest [possible], and that, nevertheless, the
state of a thing passes in its alteration through all these parts,
as elements, to its second state. In the [field of] appearance
there is no difference of the real that is the smallest, just as in
the magnitude of times there is no time that is the smallest;
and the new state of reality accordingly proceeds from the
first wherein this reality was not, through all the infinite
degrees, the differences of which from one another are all smaller
than that between 0 and a.
While we are not concerned to enquire what utility this
principle may have in the investigation of nature, what does
imperatively call for investigation is the question how such a
principle, which seems to extend our knowledge of nature, can
be possible completely a priori. Such an enquiry cannot be
dispensed with, even though direct inspection may show the principle
to be true and [empirically] real, and though the question, B255
how it should be possible, may therefore be considered
superfluous. For there are so many ungrounded claims to the
extension of our knowledge through pure reason, that we must
take it as a universal principle that any such pretension is of
itself a ground for being always mistrustful, and that, in the
absence of evidence afforded by a thoroughgoing deduction, A210
we may not believe and assume the justice of such claims, no
matter how clear the dogmatic proof of them may appear to be.
All increase in empirical knowledge, and every advance of
perception, no matter what the objects may be, whether appearances
or pure intuitions, is nothing but an extension of the
determination of inner sense, that is, an advance in time. This
advance in time determines everything, and is not in itself
determined through anything further. That is to say, its parts are
given only in time, and only through the synthesis of time; they
are not given antecedently to the synthesis. For this reason
every transition in perception to something which follows in
time is a determination of time through the generation of this
perception, and since time is always and in all its parts a
magnitude, is likewise the generation of a perception as a magnitude
through all degrees of which no one is the smallest, from zero
up to its determinate degree. This reveals the possibility of
knowing a priori a law of alterations, in respect of their form.
We are merely anticipating our own apprehension, the formal B256
condition of which, since it dwells in us prior to all appearance
that is given, must certainly be capable of being known a priori.
In the same manner, therefore, in which time contains the
sensible a priori condition of the possibility of a continuous
advance of the existing to what follows, the understanding,
by virtue of the unity of apperception, is the a priori condition A211
of the possibility of a continuous determination of all positions
for the appearances in this time, through the series of 
causes and effects, the former of which inevitably lead to the
existence of the latter, and so render the empirical knowledge
of the time-relations valid universally for all time, and
therefore objectively valid.

Refutation of Idealism

Idealism -- meaning thereby material idealism -- is the
theory which declares the existence of objects in space outside
us either to be merely doubtful and indemonstrable or to
be false and impossible. The former is the problematic idealism
of Descartes, which holds that there is only one empirical
assertion that is indubitably certain, namely, that 'I am'. The
latter is the dogmatic idealism of Berkeley. He maintains that
space, with all the things of which it is the inseparable condition,
is something which is in itself impossible; and he therefore
regards the things in space as merely imaginary entities.
Dogmatic idealism is unavoidable, if space be interpreted as a
property that must belong to things in themselves. For in that
case space, and everything to which it serves as condition, is a
non-entity. The ground on which this idealism rests has
already been undermined by us in the Transcendental Aesthetic.
Problematic idealism, which makes no such assertion, but
merely pleads incapacity to prove, through immediate experience, B275
any existence except our own, is, in so far as it allows
of no decisive judgment until sufficient proof has been found,
reasonable and in accordance with a thorough and philosophical
mode of thought. The required proof must, therefore,
show that we have experience, and not merely imagination of
outer things; and this, it would seem, cannot be achieved save
by proof that even our inner experience, which for Descartes
is indubitable, is possible only on the assumption of outer

The mere, but empirically determined, consciousness of my
own existence proves the existence of objects in space
outside me.
I am conscious of my own existence as determined in
time. All determination of time presupposes something
permanent in perception. But this permanent cannot be an intuition
in me.  For all grounds of determination of my existence which
are to be met within me are representations; and as representations
themselves require a permanent distinct from them, in relation to
which their change, and so my existence in the time wherein they
change, may be determined. Thus perception of this permanent
is possible only through a thing outside me and not through the mere
representation of a thing outside me; and consequently the
determination of my existence in time is possible only through
the existence of actual things which I perceive outside me. B276
Now consciousness [of my existence] in time is necessarily
bound up with consciousness of the [condition of the] possibility
of this time-determination; and it is therefore necessarily
bound up with the existence of things outside me, as the
condition of the time-determination. In other words, the
consciousness of my existence is at the same time an immediate
consciousness of the existence of other things outside me.
Note 1. It will be observed that in the foregoing proof
the game played by idealism has been turned against itself,
and with greater justice. Idealism assumed that the only
immediate experience is inner experience, and that from it
we can only infer outer things -- and this, moreover, only in an
untrustworthy manner, as in all cases where we are inferring
from given effects to determinate causes. In this particular case,
the cause of the representations, which we ascribe, perhaps
falsely, to outer things, may lie in ourselves. But in the above
proof it has been shown that outer experience is really
immediate, and that only by means of it is inner experience B277
-- not indeed the consciousness of my own existence, but the
determination of it in time -- possible.1 Certainly, the
representation 'I am', which expresses the consciousness that can
accompany all thought, immediately includes in itself the
existence of a subject; but it does not so include any knowledge
of that subject, and therefore also no empirical knowledge,
that is, no experience of it. For this we require, in addition to
the thought of something existing, also intuition, and in this
case inner intuition, in respect of which, that is, of time, the
subject must be determined. But in order so to determine it,
outer objects are quite indispensable; and it therefore follows
that inner experience is itself possible only mediately, and
only through outer experience.
Note 2. With this thesis all employment of our cognitive
faculty in experience, in the determination of time, entirely
agrees. Not only are we unable to perceive any determination
of time save through change in outer relations
(motion) relatively to the permanent in space (for instance,
the motion of the sun relatively to objects on the earth), we
have nothing permanent on which, as intuition, we can base B278
the concept of a substance, save only matter; and even this
permanence is not obtained from outer experience, but is
presupposed a priori as a necessary condition of determination
of time, and therefore also as a determination of inner
sense in respect of [the determination of] our own existence
through the existence of outer things.
The consciousness of myself in the representation 'I' is not an intuition, but a
merely intellectual representation of the spontaneity of a
thinking subject. This 'I' has not, therefore, the least
predicate of intuition, which, as permanent, might serve as
correlate for the determination of time in inner sense -- in the
manner in which, for instance, impenetrability serves in our
empirical intuition of matter.
Note 3. From the fact that the existence of outer things
is required for the possibility of a determinate consciousness
of the self, it does not follow that every intuitive representation
of outer things involves the existence of these things,
for their representation can very well be the product merely
of the imagination (as in dreams and delusions). Such
representation is merely the reproduction of previous outer
perceptions, which, as has been shown, are possible only
through the reality of outer objects. All that we have here
sought to prove is that inner experience in general is possible
only through outer experience in general. Whether this or that B279
supposed experience be not purely imaginary, must be ascertained
from its special determinations, and through its
congruence with the criteria of all real experience.


The immediate consciousness of the existence of outer things
is, in the preceding thesis, not presupposed, but proved, be the
possibility of this consciousness understood by us or not. The
question as to its possibility would be this: whether we have an inner
sense only, and no outer sense, but merely an outer imagination. It
is clear, however, that in order even only to imagine something as
outer, that is, to present it to sense in intuition, we must already
have an outer sense, and must thereby immediately distinguish the
mere receptivity of an outer intuition from the spontaneity which
characterises every act of imagination. For should we merely be
imagining an outer sense, the faculty of intuition, which is to be
determined by the faculty of imagination, would itself be annulled.