Immanuel Kant – The Critique of Pure Reason; Part 9


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Principle of Coexistence, According to the Law of Reciprocity or

All substances, in so far as they can be perceived in space at the same
Time, exist in a state of complete reciprocity of action


Things are coexistent, when in empirical intuition the perception of the
One can follow upon the perception of the other, and vice versa--which
Cannot occur in the succession of phenomena, as we have shown in the
Explanation of the second principle. Thus I can perceive the moon and
Then the earth, or conversely, first the earth and then the moon; and
For the reason that my perceptions of these objects can reciprocally
Follow each other, I say, they exist contemporaneously. Now coexistence
Is the existence of the manifold in the same time. But time itself is
Not an object of perception; and therefore we cannot conclude from the
Fact that things are placed in the same time, the other fact, that
The perception of these things can follow each other reciprocally. The
Synthesis of the imagination in apprehension would only present to us
Each of these perceptions as present in the subject when the other is
Not present, and contrariwise; but would not show that the objects are
Coexistent, that is to say, that, if the one exists, the other also
Exists in the same time, and that this is necessarily so, in order that
The perceptions may be capable of following each other reciprocally
It follows that a conception of the understanding or category of the
Reciprocal sequence of the determinations of phenomena (existing, as
They do, apart from each other, and yet contemporaneously), is requisite
To justify us in saying that the reciprocal succession of perceptions
Has its foundation in the object, and to enable us to represent
Coexistence as objective. But that relation of substances in which
The one contains determinations the ground of which is in the other
Substance, is the relation of influence. And, when this influence is
Reciprocal, it is the relation of community or reciprocity. Consequently
The coexistence of substances in space cannot be cognized in experience
Otherwise than under the precondition of their reciprocal action. This
Is therefore the condition of the possibility of things themselves as
Objects of experience

Things are coexistent, in so far as they exist in one and the same time
But how can we know that they exist in one and the same time? Only
By observing that the order in the synthesis of apprehension of the
Manifold is arbitrary and a matter of indifference, that is to say, that
It can proceed from A, through B, C, D, to E, or contrariwise from E
To A. For if they were successive in time (and in the order, let
Us suppose, which begins with A), it is quite impossible for the
Apprehension in perception to begin with E and go backwards to A
Inasmuch as A belongs to past time and, therefore, cannot be an object
Of apprehension

Let us assume that in a number of substances considered as phenomena
Each is completely isolated, that is, that no one acts upon another
Then I say that the coexistence of these cannot be an object of
Possible perception and that the existence of one cannot, by any mode of
Empirical synthesis, lead us to the existence of another. For we imagine
Them in this case to be separated by a completely void space, and thus
Perception, which proceeds from the one to the other in time, would
Indeed determine their existence by means of a following perception, but
Would be quite unable to distinguish whether the one phenomenon follows
Objectively upon the first, or is coexistent with it

Besides the mere fact of existence, then, there must be something by
Means of which A determines the position of B in time and, conversely
B the position of A; because only under this condition can substances
Be empirically represented as existing contemporaneously. Now that alone
Determines the position of another thing in time which is the cause of
It or of its determinations. Consequently every substance (inasmuch
As it can have succession predicated of it only in respect of its
Determinations) must contain the causality of certain determinations in
Another substance, and at the same time the effects of the causality of
The other in itself. That is to say, substances must stand (mediately or
Immediately) in dynamical community with each other, if coexistence is
To be cognized in any possible experience. But, in regard to objects of
Experience, that is absolutely necessary without which the experience of
These objects would itself be impossible. Consequently it is absolutely
Necessary that all substances in the world of phenomena, in so far
As they are coexistent, stand in a relation of complete community of
Reciprocal action to each other

The word community has in our language [Footnote: German] two meanings
And contains the two notions conveyed in the Latin communio and
Commercium. We employ it in this place in the latter sense--that of a
Dynamical community, without which even the community of place (communio
Spatii) could not be empirically cognized. In our experiences it is easy
To observe that it is only the continuous influences in all parts of
Space that can conduct our senses from one object to another; that the
Light which plays between our eyes and the heavenly bodies produces a
Mediating community between them and us, and thereby evidences their
Coexistence with us; that we cannot empirically change our position
(perceive this change), unless the existence of matter throughout the
Whole of space rendered possible the perception of the positions we
Occupy; and that this perception can prove the contemporaneous existence
Of these places only through their reciprocal influence, and thereby
Also the coexistence of even the most remote objects--although in this
Case the proof is only mediate. Without community, every perception (of
A phenomenon in space) is separated from every other and isolated, and
The chain of empirical representations, that is, of experience, must
With the appearance of a new object, begin entirely de novo, without the
Least connection with preceding representations, and without standing
Towards these even in the relation of time. My intention here is by no
Means to combat the notion of empty space; for it may exist where our
Perceptions cannot exist, inasmuch as they cannot reach thereto, and
Where, therefore, no empirical perception of coexistence takes place
But in this case it is not an object of possible experience

The following remarks may be useful in the way of explanation. In the
Mind, all phenomena, as contents of a possible experience, must exist in
Community (communio) of apperception or consciousness, and in so far as
It is requisite that objects be represented as coexistent and connected
In so far must they reciprocally determine the position in time of each
Other and thereby constitute a whole. If this subjective community is
To rest upon an objective basis, or to be applied to substances as
Phenomena, the perception of one substance must render possible the
Perception of another, and conversely. For otherwise succession, which
Is always found in perceptions as apprehensions, would be predicated of
External objects, and their representation of their coexistence be thus
Impossible. But this is a reciprocal influence, that is to say, a
Real community (commercium) of substances, without which therefore the
Empirical relation of coexistence would be a notion beyond the reach of
Our minds. By virtue of this commercium, phenomena, in so far as
They are apart from, and nevertheless in connection with each other
Constitute a compositum reale. Such composita are possible in many
Different ways. The three dynamical relations then, from which all
Others spring, are those of inherence, consequence, and composition

These, then, are the three analogies of experience. They are nothing
More than principles of the determination of the existence of phenomena
In time, according to the three modi of this determination; to wit, the
Relation to time itself as a quantity (the quantity of existence, that
Is, duration), the relation in time as a series or succession, finally
The relation in time as the complex of all existence (simultaneity)
This unity of determination in regard to time is thoroughly dynamical;
That is to say, time is not considered as that in which experience
Determines immediately to every existence its position; for this is
Impossible, inasmuch as absolute time is not an object of perception
By means of which phenomena can be connected with each other. On
The contrary, the rule of the understanding, through which alone
The existence of phenomena can receive synthetical unity as regards
Relations of time, determines for every phenomenon its position in time
And consequently a priori, and with validity for all and every time

By nature, in the empirical sense of the word, we understand the
Totality of phenomena connected, in respect of their existence
According to necessary rules, that is, laws. There are therefore certain
Laws (which are moreover a priori) which make nature possible; and all
Empirical laws can exist only by means of experience, and by virtue of
Those primitive laws through which experience itself becomes possible
The purpose of the analogies is therefore to represent to us the unity
Of nature in the connection of all phenomena under certain exponents
The only business of which is to express the relation of time (in so far
As it contains all existence in itself) to the unity of apperception
Which can exist in synthesis only according to rules. The combined
Expression of all is this: "All phenomena exist in one nature, and
Must so exist, inasmuch as without this a priori unity, no unity of
Experience, and consequently no determination of objects in experience
Is possible."

As regards the mode of proof which we have employed in treating of these
Transcendental laws of nature, and the peculiar character of we must
Make one remark, which will at the same time be important as a guide
In every other attempt to demonstrate the truth of intellectual and
Likewise synthetical propositions a priori. Had we endeavoured to prove
These analogies dogmatically, that is, from conceptions; that is to say
Had we employed this method in attempting to show that everything which
Exists, exists only in that which is permanent--that every thing or
Event presupposes the existence of something in a preceding state
Upon which it follows in conformity with a rule--lastly, that in the
Manifold, which is coexistent, the states coexist in connection with
Each other according to a rule, all our labour would have been utterly
In vain. For more conceptions of things, analyse them as we may, cannot
Enable us to conclude from the existence of one object to the existence
Of another. What other course was left for us to pursue? This only, to
Demonstrate the possibility of experience as a cognition in which
At last all objects must be capable of being presented to us, if the
Representation of them is to possess any objective reality. Now in this
Third, this mediating term, the essential form of which consists in
The synthetical unity of the apperception of all phenomena, we found
A priori conditions of the universal and necessary determination as
To time of all existences in the world of phenomena, without which the
Empirical determination thereof as to time would itself be impossible
And we also discovered rules of synthetical unity a priori, by means of
Which we could anticipate experience. For want of this method, and from
The fancy that it was possible to discover a dogmatical proof of the
Synthetical propositions which are requisite in the empirical employment
Of the understanding, has it happened that a proof of the principle of
Sufficient reason has been so often attempted, and always in vain
The other two analogies nobody has ever thought of, although they have
Always been silently employed by the mind,* because the guiding thread
Furnished by the categories was wanting, the guide which alone can
Enable us to discover every hiatus, both in the system of conceptions
And of principles

[*Footnote: The unity of the universe, in which all phenomena to be
Connected, is evidently a mere consequence of the admitted principle
Of the community of all substances which are coexistent. For were
Substances isolated, they could not as parts constitute a whole, and
Were their connection (reciprocal action of the manifold) not necessary
From the very fact of coexistence, we could not conclude from the fact
Of the latter as a merely ideal relation to the former as a real one. We
Have, however, shown in its place that community is the proper ground
Of the possibility of an empirical cognition of coexistence, and that
We may therefore properly reason from the latter to the former as its


1. That which agrees with the formal conditions (intuition and
Conception) of experience, is possible

2. That which coheres with the material conditions of experience
(sensation), is real

3. That whose coherence with the real is determined according to
Universal conditions of experience is (exists) necessary


The categories of modality possess this peculiarity, that they do not in
The least determine the object, or enlarge the conception to which they
Are annexed as predicates, but only express its relation to the faculty
Of cognition. Though my conception of a thing is in itself complete, I
Am still entitled to ask whether the object of it is merely possible
Or whether it is also real, or, if the latter, whether it is also
Necessary. But hereby the object itself is not more definitely
Determined in thought, but the question is only in what relation it
Including all its determinations, stands to the understanding and its
Employment in experience, to the empirical faculty of judgement, and to
The reason of its application to experience

For this very reason, too, the categories of modality are nothing
More than explanations of the conceptions of possibility, reality, and
Necessity, as employed in experience, and at the same time, restrictions
Of all the categories to empirical use alone, not authorizing the
Transcendental employment of them. For if they are to have something
More than a merely logical significance, and to be something more than
A mere analytical expression of the form of thought, and to have a
Relation to things and their possibility, reality, or necessity, they
Must concern possible experience and its synthetical unity, in which
Alone objects of cognition can be given

The postulate of the possibility of things requires also, that the
Conception of the things agree with the formal conditions of our
Experience in general. But this, that is to say, the objective form of
Experience, contains all the kinds of synthesis which are requisite for
The cognition of objects. A conception which contains a synthesis
Must be regarded as empty and, without reference to an object, if its
Synthesis does not belong to experience--either as borrowed from it
And in this case it is called an empirical conception, or such as is the
Ground and a priori condition of experience (its form), and in this
Case it is a pure conception, a conception which nevertheless belongs to
Experience, inasmuch as its object can be found in this alone. For where
Shall we find the criterion or character of the possibility of an object
Which is cogitated by means of an a priori synthetical conception, if
Not in the synthesis which constitutes the form of empirical cognition
Of objects? That in such a conception no contradiction exists is indeed
A necessary logical condition, but very far from being sufficient
To establish the objective reality of the conception, that is, the
Possibility of such an object as is thought in the conception. Thus, in
The conception of a figure which is contained within two straight lines
There is no contradiction, for the conceptions of two straight lines and
Of their junction contain no negation of a figure. The impossibility in
Such a case does not rest upon the conception in itself, but upon the
Construction of it in space, that is to say, upon the conditions of
Space and its determinations. But these have themselves objective
Reality, that is, they apply to possible things, because they contain a
Priori the form of experience in general

And now we shall proceed to point out the extensive utility and
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


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


The simple but empirically determined consciousness of my own existence
Proves the existence of external objects in space


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 has 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

[*Footnote: 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

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