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 accompany 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 become
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 permanent that can correspond and be submitted to
the conception of a substance as intuition, except matter. This idea
of permanence is not itself derived from external experience, but is
an a priori necessary condition of all determination of time,
consequently also of the internal sense in reference to our own
existence, and that through the existence of external things. In the
representation "I," the consciousness of myself is not an intuition,
but a merely intellectual representation produced by the spontaneous
activity of a thinking subject. It follows, that this
I has not
any predicate of intuition, which, in its character of permanence,
could serve as correlate to the determination of time in the
internal sense— in the same way as impenetrability is the correlate of
matter as an empirical intuition.
Remark III. From the fact that the existence of external things is a
necessary condition of the possibility of a determined consciousness
of ourselves, it does not follow that every intuitive representation
of external things involves the existence of these things, for their
representations may very well be the mere products of the
imagination (in dreams as well as in madness); though, indeed, these
are themselves created by the reproduction of previous external
perceptions, which, as has been shown, are possible only through the
reality of external objects. The sole aim of our remarks has, however,
been to prove that internal experience in general is possible only
through external experience in general. Whether this or that
supposed experience be purely imaginary must be discovered from its
particular determinations and by comparing these with the criteria
of all real experience.
Finally, as regards the third postulate, it applies to material
necessity in existence, and not to merely formal and logical necessity
in the connection of conceptions. Now as we cannot cognize
completely a priori the existence of any object of sense, though we
can do so comparatively a priori, that is, relatively to some other
previously given existence— a cognition, however, which can only be of
such an existence as must be contained in the complex of experience,
of which the previously given perception is a part— the necessity of
existence can never be cognized from conceptions, but always, on the
contrary, from its connection with that which is an object of
perception. But the only existence cognized, under the condition of
other given phenomena, as necessary, is the existence of effects
from given causes in conformity with the laws of causality. It is
consequently not the necessity of the existence of things (as
substances), but the necessity of the state of things that we cognize,
and that not immediately, but by means of the existence of other
states given in perception, according to
empirical laws of
causality. Hence it follows that the criterion of necessity is to be
found only in the law of possible experience— that everything which
happens is determined
a priori in the phenomenon by its cause. Thus we
cognize only the necessity of
effects in nature, the causes of which
are given us. Moreover, the criterion of necessity in existence
possesses no application beyond the field of possible experience,
and even in this it is not valid of the existence of things as
substances, because these can never be considered as empirical
effects, or as something that happens and has a beginning.
Necessity, therefore, regards only the relations of phenomena
according to the dynamical law of causality, and the possibility
grounded thereon, of reasoning from some given existence (of a
cause)
a priori to another existence (of an effect).
Everything
that happens is hypothetically necessary, is a principle which
subjects the changes that take place in the world to a law, that is,
to a rule of necessary existence, without which nature herself could
not possibly exist. Hence the proposition,
Nothing happens by blind
chance (
in mundo non datur casus), is an
a priori law of nature.
The case is the same with the proposition,
Necessity in nature is not
blind, that is, it is conditioned, consequently intelligible
necessity (
non datur fatum). Both laws subject the play of change to
a nature of things (as phenomena), or, which is the same thing, to
the unity of the understanding, and through the understanding alone
can changes belong to an experience, as the synthetical unity of
phenomena. Both belong to the class of dynamical principles. The
former is properly a consequence of the principle of causality— one of
the analogies of experience. The latter belongs to the principles of
modality, which to the determination of causality adds the
conception of necessity, which is itself, however, subject to a rule
of the understanding. The principle of continuity forbids any
leap
in the series of phenomena regarded as changes (
in mundo non datur
saltus); and likewise, in the complex of all empirical intuitions in
space, any break or hiatus between two phenomena (
non datur hiatus)—
for we can so express the principle, that experience can admit nothing
which proves the existence of a vacuum, or which even admits it as a
part of an empirical synthesis. For, as regards a vacuum or void,
which we may cogitate as out and beyond the field of possible
experience
(the world), such a question cannot come before the
tribunal of mere understanding, which decides only upon questions that
concern the employment of given phenomena for the construction of
empirical cognition. It is rather a problem for ideal reason, which
passes beyond the sphere of a possible experience and aims at
forming a judgement of that which surrounds and circumscribes it,
and the proper place for the consideration of it is the transcendental
dialectic. These four propositions,
In mundo non datur hiatus, non
datur saltus, non datur casus, non datur fatum, as well as all
principles of transcendental origin, we could very easily exhibit in
their proper order, that is, in conformity with the order of the
categories, and assign to each its proper place. But the already
practised reader will do this for himself, or discover the clue to
such an arrangement. But the combined result of all is simply this, to
admit into the empirical synthesis nothing which might cause a break
in or be foreign to the understanding and the continuous connection of
all phenomena, that is, the unity of the conceptions of the
understanding. For in the understanding alone is the unity of
experience, in which all perceptions must have their assigned place,
possible.
Whether the field of possibility be greater than that of reality,
and whether the field of the latter be itself greater than that of
necessity, are interesting enough questions, and quite capable of
synthetic solution, questions, however, which come under the
jurisdiction of reason alone. For they are tantamount to asking
whether all things as phenomena do without exception belong to the
complex and connected whole of a single experience, of which every
given perception is a part which therefore cannot be conjoined with
any other phenomena— or, whether my perceptions can belong to more
than one possible experience? The understanding gives to experience,
according to the subjective and formal conditions, of sensibility as
well as of apperception, the rules which alone make this experience
possible. Other forms of intuition besides those of space and time,
other forms of understanding besides the discursive forms of
thought, or of cognition by means of conceptions, we can neither
imagine nor make intelligible to ourselves; and even if we could, they
would still not belong to experience, which is the only mode of
cognition by which objects are presented to us. Whether
other
perceptions besides those which belong to the total of our possible
experience, and consequently whether some other sphere of matter
exists, the understanding has no power to decide, its proper
occupation being with the synthesis of that which is given.
Moreover, the poverty of the usual arguments which go to prove the
existence of a vast sphere of possibility, of which all that is real
(every object of experience) is but a small part, is very
remarkable. "All real is possible"; from this follows naturally,
according to the logical laws of conversion, the particular
proposition: "Some possible is real." Now this seems to be
equivalent to: "Much is possible that is not real." No doubt it does
seem as if we ought to consider the sum of the possible to be
greater than that of the real, from the fact that something must be
added to the former to constitute the latter. But this notion of
adding to the possible is absurd. For that which is not in the sum
of the possible, and consequently requires to be added to it, is
manifestly impossible. In addition to accordance with the formal
conditions of experience, the understanding requires a connection with
some perception; but that which is connected with this perception is
real, even although it is not immediately perceived. But that
another series of phenomena, in complete coherence with that which
is given in perception, consequently more than one all—embracing
experience is possible, is an inference which cannot be concluded from
the data given us by experience, and still less without any data at
all. That which is possible only under conditions which are themselves
merely possible, is not possible
in any respect. And yet we can find
no more certain ground on which to base the discussion of the question
whether the sphere of possibility is wider than that of experience.
I have merely mentioned these questions, that in treating of the
conception of the understanding, there might be no omission of
anything that, in the common opinion, belongs to them. In reality,
however, the notion of absolute possibility (possibility which is
valid in every respect) is not a mere conception of the understanding,
which can be employed empirically, but belongs to reason alone,
which passes the bounds of all empirical use of the understanding.
We have, therefore, contented ourselves with a merely critical remark,
leaving the subject to be explained in the sequel.
Before concluding this fourth section, and at the same time the
system of all principles of the pure understanding, it seems proper to
mention the reasons which induced me to term the principles of
modality postulates. This expression I do not here use in the sense
which some more recent philosophers, contrary to its meaning with
mathematicians, to whom the word properly belongs, attach to it—
that of a proposition, namely, immediately certain, requiring
neither deduction nor proof. For if, in the case of synthetical
propositions, however evident they may be, we accord to them without
deduction, and merely on the strength of their own pretensions,
unqualified belief, all critique of the understanding is entirely
lost; and, as there is no want of bold pretensions, which the common
belief (though for the philosopher this is no credential) does not
reject, the understanding lies exposed to every delusion and
conceit, without the power of refusing its assent to those assertions,
which, though illegitimate, demand acceptance as veritable axioms.
When, therefore, to the conception of a thing an a priori
determination is synthetically added, such a proposition must
obtain, if not a proof, at least a deduction of the legitimacy of
its assertion.
The principles of modality are, however, not objectively
synthetical, for the predicates of possibility, reality, and necessity
do not in the least augment the conception of that of which they are
affirmed, inasmuch as they contribute nothing to the representation of
the object. But as they are, nevertheless, always synthetical, they
are so merely subjectively. That is to say, they have a reflective
power, and apply to the conception of a thing, of which, in other
respects, they affirm nothing, the faculty of cognition in which the
conception originates and has its seat. So that if the conception
merely agree with the formal conditions of experience, its object is
called possible; if it is in connection with perception, and
determined thereby, the object is real; if it is determined
according to conceptions by means of the connection of perceptions,
the object is called necessary. The principles of modality therefore
predicate of a conception nothing more than the procedure of the
faculty of cognition which generated it. Now a postulate in
mathematics is a practical proposition which contains nothing but
the synthesis by which we present an object to ourselves, and
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.