2. What is connected with the material conditions of experience (sensation) is real
3. That which, in its connection with the real, is determined by universal conditions of experience, is (exists as) necessary
Explanation
The categories of modality have this peculiar character that, as determining an object, they do not enlarge in the least the concept to which they are attached as predicates, but express only a relation to our faculty of knowledge. Even when the concept of a thing is quite complete, I can still ask with reference to that object, whether it is possible only, or real also, and, if the latter, whether it is necessary? No new determinations of the object are thereby conceived, but it is only asked in what relation it (with all its determinations) stands to the understanding and its empirical employment, to the empirical faculty of judgment, and to reason, in its application to experience?
The principles of modality are therefore nothing but explanations of the concepts of possibility, reality, and necessity, in their empirical employment, confining all categories to an empirical employment only, and prohibiting their transcendental18 use. For if these categories are not to have a purely logical character, expressing the forms of thought analytically, but are to refer to things, their possibility, reality, or necessity, they must have reference to possible experience and its synthetical unity, in which alone objects of knowledge can be given.
The postulate of the possibility of things demands that the concept of these should agree with the formal conditions of experience in general. This, the objective form of experience in general, contains all synthesis which is required for a knowledge of objects. A concept is to be considered as empty, and as referring to no object, if the synthesis which it contains does not belong to experience, whether as borrowed from it (in which case it is called an empirical concept), or as a synthesis on which, as a condition a priori, all experience (in its form) depends, in which case it is a pure concept, but yet belonging to experience, because its object can only be found in it. For whence could the character of the possibility of an object, which can be conceived by a synthetical concept a priori, be derived, except from the synthesis which constitutes the form of all empirical knowledge of objects? It is no doubt a necessary logical condition, that such a concept must contain nothing contradictory, but this is by no means sufficient to establish the objective reality of a concept, that is, the possibility of such an object, as is conceived by a concept. Thus in the concept of a figure to be enclosed between two straight lines, there is nothing contradictory, because the concepts of two straight lines and their meeting contain no negation of a figure. The impossibility depends, not on the concept itself, but on its construction in space, that is, the conditions of space and its determinations, and it is these that have objective reality, or apply to possible things, because they contain a priori in themselves the form of experience in general.
And now we shall try to explain the manifold usefulness and influence of this postulate of possibility. If I represent to myself a thing that is permanent, while everything which changes belongs merely to its state, I can never know from such a concept by itself that a thing of that kind is possible. Or, if I represent to myself something so constituted that, when it is given, something else must at all times and inevitably follow upon it, this may no doubt be conceived without contradiction, but we have as yet no means of judging whether such a quality, viz. causality, is to be met with in any possible object. Lastly, I can very well represent to myself different things (substances) so constituted, that the state of the one produces an effect on the state of the other, and this reciprocally; but whether such a relation can belong to any things cannot be learned from these concepts which contain a purely arbitrary synthesis. The objective reality of these concepts is only known when we see that they express a priori the relations of perceptions in every kind of experience; and this objective reality, that is, their transcendental truth, though independent of all experience, is nevertheless not independent of all relation to the form of experience in general, and to that synthetical unity in which alone objects can be known empirically.
But if we should think of framing new concepts of substances, forces, and reciprocal actions out of the material supplied to us by our perceptions, without borrowing from experience the instance of their connection, we should entangle ourselves in mere cobwebs of our brain, the possibility of which could not be tested by any criteria, because in forming them we were not guided by experience, nor had borrowed these concepts from it. Such purely imaginary concepts cannot receive the character of possibility, like the categories a priori, as conditions on which all experience depends, but only a posteriori, as concepts that must be given by experience, so that their possibility can either not be known at all, or a posteriori, and empirically only. Thus, for instance, a substance supposed to be present as permanent in space, and yet not filling it (like that something between matter and the thinking subject, which some have tried to introduce), or a peculiar faculty of our mind, by which we can see (not only infer) the future, or lastly, another faculty, by which we can enter into a community of thought with other men (however distant they may be), all these are concepts the possibility of which has nothing to rest on, because it is not founded on experience and its known laws. Without these they are and can only be arbitrary combinations of thought which, though they contain nothing contradictory in themselves, have no claim to objective reality, or to the possibility of such an object as is to be conceived by them. With regard to reality, it stands to reason that we cannot conceive it in the concrete without the aid of experience; for reality concerns sensation only, as the material of experience, and not the form of relations, which might to a certain extent allow us to indulge in mere fancies.
I here pass by everything the possibility of which can only be learned from its reality in experience, and I only mean to consider the possibility of things through concepts a priori. Of these (concepts) I persist in maintaining that they can never exist as such concepts by themselves alone, but only as formal and objective conditions of experience in general.19
It might seem indeed as if the possibility of a triangle could be known from its concept by itself (being independent of all experience), for we can give to it an object entirely a priori, that is, we can construct it. But as this is only the form of an object, it would always remain a product of the imagination only. The possibility of its object would remain doubtful, because more is wanted to establish it, namely, that such a figure should really be conceived under all those conditions on which all objects of experience depend. That which alone connects with this concept the representation of the possibility of such a thing is the fact that space is a formal condition a priori of all external experiences, and that the same formative synthesis, by which we construct a triangle in imagination, should be identical with that which we exercise in the apprehension of a phenomenon, in order to make an empirical concept of it. And thus the possibility of continuous quantities, nay, of all quantities, the concepts of which are always synthetical, can never be deduced from the concepts themselves, but only from them, as formal conditions of the determination of objects in all experience. And where indeed should we look for objects, corresponding to our concepts, except in experience, by which alone objects are given us? If we are able to know and determine the possibility of things without any previous experience, this is only with reference to those formal conditions under which anything may become an object in experience. This takes place entirely a priori, but nevertheless in constant reference to experience, and within its limits.
The postulate concerning our knowledge of the reality of things, requires perception, therefore sensation and consciousness of it, not indeed immediately of the object itself, the existence of which is to be known, but yet of a connection between it and some real perception, according to the analogies of experience which determine in general all real combinations in experience.
In the mere concept of a thing no sign
of its existence can be discovered. For though the concept be ever so perfect, so that nothing should be wanting in it to enable us to conceive the thing with all its own determinations, existence has nothing to do with all this. It depends only on the question whether such a thing be given us, so that its perception may even precede its concept. A concept preceding experience implies its possibility only, while perception, which supplies the material of a concept, is the only characteristic of reality. It is possible, however, even before the perception of a thing, and therefore, in a certain sense, a priori, to know its existence, provided it hang together with some other perceptions, according to the principles of their empirical connection (analogies). For in that case the existence of a thing hangs together at least with our perceptions in a possible experience, and guided by our analogies we can, starting from our real experience, arrive at some other thing in the series of possible perceptions. Thus we know the existence of some magnetic matter pervading all bodies from the perception of the attracted iron filings, though our organs are so constituted as to render an immediate perception of that matter impossible. According to the laws of sensibility and the texture of our perceptions, we ought in our experience to arrive at an immediate empirical intuition of that magnetic matter, if only our senses were more acute, for their actual obtuseness does not concern the form of possible experience. Wherever, therefore, perception and its train can reach, according to empirical laws, there our knowledge also of the existence of things can reach. But if we do not begin with experience, or do not proceed according to the laws of the empirical connection of phenomena, we are only making a vain display, as if we could guess and discover the existence of anything.20
With reference to the third postulate we find that it refers to the material necessity in existence, and not to the merely formal and logical necessity in the connection of concepts. As it is impossible that the existence of the objects of the senses should ever be known entirely a priori, though it may be known to a certain extent a priori, namely, with reference to another already given existence, and as even in that case we can only arrive at such an existence as must somewhere be contained in the whole of the experience of which the given perception forms a part, it follows that the necessity of existence can never be known from concepts, but always from the connection only with what is actually perceived, according to general rules of experience.21 Now, there is no existence that can be known as necessary under the condition of other given phenomena, except the existence of effects from given causes, according to the laws of causality. It is not therefore the existence of things (substances), but the existence of their state, of which alone we can know the necessity, and this from other states only, which are given in perception, and according to the empirical laws of causality. Hence it follows that the criterium of necessity can only be found in the law of possible experience, viz. that everything that happens is determined a priori by its cause in phenomena.22 We therefore know in nature the necessity of those effects only of which the causes are given, and the character of necessity in existence never goes beyond the field of possible experience, and even there it does not apply to the existence of things, as substances, because such substances can never be looked upon as empirical effects or as something that happens and arises. Necessity, therefore, affects only the relations of phenomena according to the dynamical law of causality, and the possibility, dependent upon it, of concluding a priori from a given existence (of a cause) to another existence (that of an effect). Thus the principle that everything which happens is hypothetically necessary, subjects all the changes in the world to a law, that is, to a rule of necessary existence, without which there would not even be such a thing as nature. Hence the proposition that nothing happens by blind chance (in mundo non datur casus) is an a priori law of nature, and so is likewise the other, that no necessity in nature is a blind, but always a conditional and therefore an intelligible, necessity (non datur fatum). Both these are laws by which the mere play of changes is rendered subject to a nature of things (as phenomena), or what is the same, to that unity of the understanding in which alone they can belong to experience, as the synthetical unity of phenomena. Both are dynamical principles. The former is in reality a consequence of the principle of causality (the second of the analogies of experience). The latter is one of the principles of modality, which to the determination of causality adds the concept of necessity, which itself is subject to a rule of the understanding. The principle of continuity rendered every break in the series of phenomena (changes) impossible (in mundo non datur saltus), and likewise any gap between two phenomena in the whole of our empirical intuitions in space (non datur hiatus). For so we may express the proposition that nothing can enter into experience to prove a vacuum, or even to admit it as a possible part of empirical synthesis. For the vacuum, which one may conceive as outside the field of possible experience (the world), can never come before the tribunal of the understanding which has to decide on such questions only as concern the use to be made of given phenomena for empirical knowledge. It is in reality a problem of that ideal reason which goes beyond the sphere of a possible experience, and wants to form an opinion of that which surrounds and limits experience, and will therefore have to be considered in our transcendental Dialectic. With regard to the four propositions (in mundo non datur hiatus, non datus saltus, non datur casus, non datur fatum), it would be easy to represent each of them, as well as all principles of a transcendental origin, according to the order of the categories, and thus to assign its proper place to every one of them. But, after what has been said before, the versed and expert reader will find it easy to do this himself, and to discover the proper method for it. They all simply agree in this, that they admit nothing in our empirical synthesis that would in any way run counter to the understanding, and to the continuous cohesion of all phenomena, that is, to the unity of its concepts. For it is the understanding alone through which the unity of experience, in which all perceptions must have their place, becomes possible.
Whether the field of possibility be larger than the field which contains everything which is real, and whether this again be larger than the field of what is necessary, are curious questions and admitting of a synthetical solution, which questions however are to be brought before the tribunal of reason only. They really come to this, whether all things, as phenomena, belong to the sphere of one experience, of which every given perception forms a part, that could not be connected with any other phenomena, or whether my perceptions can ever belong to more than one possible experience (in its general connection). The understanding in reality does nothing but give to experience a rule a priori, according to the subjective and formal conditions of sensibility and apperception, which alone render experience possible. Other forms of intuition (different from space and time), and other forms of the understanding (different from the discursive forms of thought or conceptual knowledge), even if they were possible, we could in no wise render conceivable or intelligible to ourselves; and even if we could, they would never belong to experience, the only field of knowledge in which objects are given to us. Whether there be therefore other perceptions but those that belong to our whole possible experience, whether there be in fact a completely new field of matter, can never be determined by the understanding, which is only concerned with the synthesis of what is given.
The poverty of the usual arguments by which we construct a large empire of possibility of which all that is real (the objects of experience) forms but a small segment, is but too apparent. When we say that all that is real is possible, we arrive, according to the logical rules of inversion, at the merely particular proposition that some possible is real, and thus seem to imply that much is possible that is not real. Nay, it seems as if we might extend the number of things possible beyond that of things real, simply on the ground that something must be added to the possible to make it real. But this addition to the possible I cannot recognize, because what would thus be added to the possible, would be really the imposs
ible. It is only to my understanding that anything can be added concerning the agreement with the formal conditions of experience, and what can be added is the connection with some perception; and whatever is connected with such a perception, according to empirical laws, is real, though it may not be perceived immediately. But that, in constant connection with what is given us in experience, there should be another series of phenomena, and therefore more than one all-embracing experience, cannot possibly be concluded from what is given us, and still less, if nothing is given us, because nothing can be thought without some kind of material. What is possible only under conditions which themselves are possible only, is not possible in the full sense of the word, not therefore in the sense in which we ask whether the possibility of things can extend beyond the limits of experience.
I have only touched on these questions in order to leave no gap in what are commonly supposed to be the concepts of the understanding. But absolute possibility (which has no regard for the formal conditions of experience) is really no concept of the understanding, and can never be used empirically, but belongs to reason alone, which goes beyond all possible empirical use of the understanding. We have therefore made these few critical remarks only, leaving the subject itself unexplained for the present.
And here, when I am on the point of concluding this fourth number and at the same time the system of all principles of the pure understanding, I think I ought to explain why I call the principles of modality postulates. I do not take this term in the sense which has been given to it by some modern philosophical writers, and which is opposed to the sense in which mathematicians take it, viz. that to postulate should mean to represent a proposition as certain without proof or justification; for if we were to admit with regard to synthetical propositions, however evident they may appear, that they should meet with unreserved applause, without any deduction, and on their own authority only, all criticism of the understanding would be at an end. And as there is no lack of bold assertions, which public opinion does not decline to accept, (this acceptance being, however, no credential), our understanding would be open to every fancy, and could not refuse its sanction to claims which demand admission as real axioms in the same confident tone, though without any substantial reasons. If therefore a condition a priori is to be synthetically joined to the concept of a thing, it will be indispensable that, if not a proof, at least a deduction of the legitimacy of such an assertion, should be forthcoming.
Critique of Pure Reason Page 22
