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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.

GENERAL REMARK ON THE SYSTEM OF PRINCIPLES.

It is very remarkable that we cannot perceive the possibility of a

thing from the category alone, but must always have an intuition, by

which to make evident the objective reality of the pure conception

of the understanding. Take, for example, the categories of relation.

How (1) a thing can exist only as a subject, and not as a mere

determination of other things, that is, can be substance; or how

(2), because something exists, some other thing must exist,

consequently how a thing can be a cause; or how (3), when several

things exist, from the fact that one of these things exists, some

consequence to the others follows, and reciprocally, and in this way a

community of substances can be possible- are questions whose

solution cannot be obtained from mere conceptions. The very same is

the case with the other categories; for example, how a thing can be of

the same sort with many others, that is, can be a quantity, and so on.

So long as we have not intuition we cannot know whether we do really

think an object by the categories, and where an object can anywhere be

found to cohere with them, and thus the truth is established, that the

categories are not in themselves cognitions, but mere forms of thought

for the construction of cognitions from given intuitions. For the same

reason is it true that from categories alone no synthetical

proposition can be made. For example: "In every existence there is

substance," that is, something that can exist only as a subject and

not as mere predicate; or, "Everything is a quantity"- to construct

propositions such as these, we require something to enable us to go

out beyond the given conception and connect another with it. For the

same reason the attempt to prove a synthetical proposition by means of

mere conceptions, for example: "Everything that exists contingently

has a cause," has never succeeded. We could never get further than

proving that, without this relation to conceptions, we could not

conceive the existence of the contingent, that is, could not a

priori through the understanding cognize the existence of such a

thing; but it does not hence follow that this is also the condition of

the possibility of the thing itself that is said to be contingent. If,

accordingly; we look back to our proof of the principle of

causality, we shall find that we were able to prove it as valid only

of objects of possible experience, and, indeed, only as itself the

principle of the possibility of experience, Consequently of the

cognition of an object given in empirical intuition, and not from mere

conceptions. That, however, the proposition: "Everything that is

contingent must have a cause," is evident to every one merely from

conceptions, is not to be denied. But in this case the conception of

the contingent is cogitated as involving not the category of

modality (as that the non-existence of which can be conceive but

that of relation (as that which can exist only as the consequence of

something else), and so it is really an identical proposition: "That

which can exist only as a consequence, has a cause." In fact, when

we have to give examples of contingent existence, we always refer to

changes, and not merely to the possibility of conceiving the

opposite.* But change is an event, which, as such, is possible only

through a cause, and considered per se its non-existence is

therefore possible, and we become cognizant of its contingency from

the fact that it can exist only as the effect of a cause. Hence, if

a thing is assumed to be contingent, it is an analytical proposition

to say, it has a cause.

*We can easily conceive the non-existence of matter; but the

ancients did not thence infer its contingency. But even the

alternation of the existence and non-existence of a given state in a

thing, in which all change consists, by no means proves the

contingency of that state- the ground of proof being the reality of

its opposite. For example, a body is in a state of rest after

motion, but we cannot infer the contingency of the motion from the

fact that the former is the opposite of the latter. For this

opposite is merely a logical and not a real opposite to the other.

If we wish to demonstrate the contingency of the motion, what we ought

to prove is that, instead of the motion which took place in the

preceding point of time, it was possible for the body to have been

then in rest, not, that it is afterwards in rest; for in this case,

both opposites are perfectly consistent with each other.

But it is still more remarkable that, to understand the

possibility of things according to the categories and thus to

demonstrate the objective reality of the latter, we require not merely

intuitions, but external intuitions. If, for example, we take the pure

conceptions of relation, we find that (1) for the purpose of

presenting to the conception of substance something permanent in