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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 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 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