The Critique of Pure Reason

Transcendental Analytic (continua)

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 à priori the existence of any object of sense, though we can do so comparatively à 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 à 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) à 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 à 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 à 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[36] the conception of a thing but merely indicate the manner in which it is connected with the faculty of cognition.

[36] 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 à 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 conceived) 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.[37] 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.

[37] 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 intuition corresponding thereto and thus of demonstrating the objective reality of this conception, we require an intuition (of matter) in space, because space alone is permanent and determines things as such, while time, and with it all that is in the internal sense, is in a state of continual flow; (2) in order to represent change as the intuition corresponding to the conception of causality, we require the representation of motion as change in space; in fact, it is through it alone that changes, the possibility of which no pure understanding can perceive, are capable of being intuited. Change is the connection of determinations contradictorily opposed to each other in the existence of one and the same thing. Now, how it is possible that out of a given state one quite opposite to it in the same thing should follow, reason without an example can not only not conceive, but cannot even make intelligible without intuition; and this intuition is the motion of a point in space; the existence of which in different spaces (as a consequence of opposite determinations) alone makes the intuition of change possible. For, in order to make even internal change cognitable, we require to represent time, as the form of the internal sense, figuratively by a line, and the internal change by the drawing of that line (motion), and consequently are obliged to employ external intuition to be able to represent the successive existence of ourselves in different states. The proper ground of this fact is that all change to be perceived as change presupposes something permanent in intuition, while in the internal sense no permanent intuition is to be found. Lastly, the objective possibility of the category of community cannot be conceived by mere reason, and consequently its objective reality cannot be demonstrated without an intuition, and that external in space. For how can we conceive the possibility of community, that is, when several substances exist, that some effect on the existence of the one follows from the existence of the other, and reciprocally, and therefore that, because something exists in the latter, something else must exist in the former, which could not be understood from its own existence alone? For this is the very essence of community—which is inconceivable as a property of things which are perfectly isolated. Hence, Leibnitz, in attributing to the substances of the world—as cogitated by the understanding alone—a community, required the mediating aid of a divinity; for, from their existence, such a property seemed to him with justice inconceivable. But we can very easily conceive the possibility of community (of substances as phenomena) if we represent them to ourselves as in space, consequently in external intuition. For external intuition contains in itself à priori formal external relations, as the conditions of the possibility of the real relations of action and reaction, and therefore of the possibility of community. With the same ease can it be demonstrated, that the possibility of things as quantities, and consequently the objective reality of the category of quantity, can be grounded only in external intuition, and that by its means alone is the notion of quantity appropriated by the internal sense. But I must avoid prolixity, and leave the task of illustrating this by examples to the reader’s own reflection.

The above remarks are of the greatest importance, not only for the confirmation of our previous confutation of idealism, but still more when the subject of self-cognition by mere internal consciousness and the determination of our own nature without the aid of external empirical intuitions is under discussion, for the indication of the grounds of the possibility of such a cognition.

The result of the whole of this part of the analytic of principles is, therefore: “All principles of the pure understanding are nothing more than à priori principles of the possibility of experience, and to experience alone do all à priori synthetical propositions apply and relate”; indeed, their possibility itself rests entirely on this relation.

Chapter III Of the Ground of the Division of all Objects into Phenomena and Noumena