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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