What can we know?

Kant’s “dogmatic slumber”

Since the Essays of Locke and Leibniz, or rather since the origin of metaphysics so far as we know its history, nothing has ever happened which was more decisive to its fate than the attack made upon it by David Hume. He threw no light on this species of knowledge, but he certainly struck a spark from which light might have been obtained, had it caught some inflammable substance and had its smoldering fire been carefully nursed and developed.

Hume started from a single but important concept in Metaphysics, viz., that of Cause and Effect (including its derivatives force and action, etc.). He challenges reason, which pretends to have given birth to this idea from herself, to answer him by what right she thinks anything to be so constituted, that if that thing be posited, something else also must necessarily be posited; for this is the meaning of the concept of cause. He demonstrated irrefutably that it was perfectly impossible for reason to think a priori and by means of concepts a combination involving necessity. We cannot at all see why, in consequence of the existence of one thing, another must necessarily exist, or how the concept of such a combination can arise a priori. Hence he inferred, that reason was altogether deluded with reference to this concept, which she erroneously considered as one of her children, whereas in reality it was nothing but a bastard of imagination, impregnated by experience, which subsumed certain representations under the Law of Association, and mistook the subjective necessity of habit for an objective necessity arising from insight. Hence he inferred that reason had no power to think such, combinations, even generally, because her concepts would then be purely fictitious, and all her pretended a priori cognitions nothing but common experiences marked with a false stamp. In plain language there is not, and cannot be, any such thing as metaphysics at all. (…)

The question was not whether the concept of cause was right, useful, and even indispensable for our knowledge of nature, for this Hume had never doubted; but whether that concept could be thought by reason a priori, and consequently whether it possessed an inner truth, independent of all experience, implying a wider application than merely to the objects of experience. This was Hume’s problem. It was a question concerning the origin, not concerning the indispensable need of the concept. Were the former decided, the conditions of the use and the sphere of its valid application would have been determined as a matter of course. (…)

I openly confess, the suggestion of David Hume was the very thing, which many years ago first interrupted my dogmatic slumber, and gave my investigations in the field of speculative philosophy quite a new direction. I was far from following him in the conclusions at which he arrived by regarding, not the whole of his problem, but a part, which by itself can give us no information. If we start from a well-founded, but undeveloped, thought, which another has bequeathed to us, we may well hope by continued reflection to advance farther than the acute man, to whom we owe the first spark of light.

Immanuel Kant, Prolegomena to Any Future Metaphysics (1783).


Reason, experience and the limits of knowledge

That all our knowledge begins with experience there can be no doubt. For how is it possible that the faculty of cognition should be awakened into exercise otherwise than by means of objects which affect our senses, and partly of themselves produce representations, partly rouse our powers of understanding into activity, to compare to connect, or to separate these, and so to convert the raw material of our sensuous impressions into a knowledge of objects, which is called experience? In respect of time, therefore, no knowledge of ours is antecedent to experience, but begins with it. But, though all our knowledge begins with experience, it by no means follows that all arises out of experience. For, on the contrary, it is quite possible that our empirical knowledge is a compound of that which we receive through impressions, and that which the faculty of cognition supplies from itself (sensuous impressions giving merely the occasion), an addition which we cannot distinguish from the original element given by sense, till long practice has made us attentive to, and skillful in separating it.

(…) Of far more importance than all that has been above said, is the consideration that certain of our cognitions rise completely above the sphere of all possible experience, and by means of conceptions, to which there exists in the whole extent of experience no corresponding object, seem to extend the range of our judgments beyond its bounds. And just in this transcendental or supersensible sphere, where experience affords us neither instruction nor guidance, lie the investigations of reason, which, on account of their importance, we consider far preferable to, and as having a far more elevated aim than, all that the understanding can achieve within the sphere of sensuous phenomena. So high a value do we set upon these investigations, that even at the risk of error, we persist in following them out, and permit neither doubt nor disregard nor indifference to restrain us from the pursuit. These unavoidable problems of mere pure reason are God, freedom (of will), and immortality. The science which, with all its preliminaries, has for its especial object the solution of these problems is named metaphysics—a science which is at the very outset dogmatical, that is, it confidently takes upon itself the execution of this task without any previous investigation of the ability or inability of reason for such an undertaking. Now the safe ground of experience being thus abandoned, it seems nevertheless natural that we should hesitate to erect a building with the cognitions we possess, without knowing whence they come, and on the strength of principles, the origin of which is undiscovered. Instead of thus trying to build without a foundation, it is rather to be expected that we should long ago have put the question, how the understanding can arrive at these a priori cognitions, and what is the extent, validity, and worth which they may possess? We say, “This is natural enough,” meaning by the word natural, that which is consistent with a just and reasonable way of thinking; but if we understand by the term, that which usually happens, nothing indeed could be more natural and more comprehensible than that this investigation should be left long unattempted. For one part of our pure knowledge, the science of mathematics, has been long firmly established, and thus leads us to form flattering expectations with regard to others, though these may be of quite a different nature. Besides, when we get beyond the bounds of experience, we are of course safe from opposition in that quarter; and the charm of widening the range of our knowledge is so great that, unless we are brought to a standstill by some evident contradiction, we hurry on undoubtingly in our course. This, however, may be avoided, if we are sufficiently cautious in the construction of our fictions, which are not the less fictions on that account. Mathematical science affords us a brilliant example, how far, independently of all experience, we may carry our a priori knowledge. It is true that the mathematician occupies himself with objects and cognitions only in so far as they can be represented by means of intuition. But this circumstance is easily overlooked, because the said intuition can itself be given a priori, and therefore is hardly to be distinguished from a mere pure conception. Deceived by such a proof of the power of reason, we can perceive no limits to the extension of our knowledge. The light dove cleaving in free flight the thin air, whose resistance it feels, might imagine that her movements would be far more free and rapid in airless space. Just in the same way did Plato, abandoning the world of sense because of the narrow limits it sets to the understanding, venture upon the wings of ideas beyond it, into the void space of pure intellect. He did not reflect that he made no real progress by all his efforts; for he met with no resistance which might serve him for a support, as it were, whereon to rest, and on which he might apply his powers, in order to let the intellect acquire momentum for its progress.

Immanuel Kant, The Critique of Pure Reason (1781, second edition 1787)


Space as an a priori condition of our experience

By means of outer sense (a property of our mind) we present objects as outside us, and present them one and all in space. In space their shape, magnitude, and relation to one another are determined or determinable: By means of inner sense the mind intuits itself, or its inner state. Although inner sense provides no intuition of the soul itself as an object, yet there is a determinate form under which alone [as condition] we can intuit the soul’s inner state. [That form is time.] Thus everything belonging’ to our inner determinations is presented in relations of time. Time cannot be intuited outwardly, any more than space can be intuited as something within us. What, then, are space and time? Are they actual beings? Are they only determinations of things, or, for that matter, relations among them? If so, are they at least determinations or relations that would belong to things intrinsically also, i.e., even if these things were not intuited? Or are they determinations and relations that adhere only to the form of intuition and hence to the subjective character of our mind, so that apart from that character these predicates cannot be ascribed to any thing at all?

(…) (1) Space is not an empirical concept that has been abstracted from outer experiences. For the presentation of space must already lie at the basis in order for certain sensations to be referred to something outside me (i.e., referred to something in a location of space other than the location in which I am). And it must similarly already lie at the basis in order for me to be able to present [the objects of] these sensations as outside and alongside one another, and hence to present them not only as different but as being in different locations. Accordingly, the presentation of space cannot be one that we take from the relations of outer appearance by means of experience; rather, only through the presentation of space is that outer experience possible in the first place.

(2) Space is a necessary a priori presentation that underlies all outer intuitions. We can never have a presentation of there being no space, even though we are quite able to think of there being no objects encountered in it. Hence space must be regarded as the condition for the possibility of appearances, and not as a determination dependent on them. Space is an a priori presentation that necessarily underlies outer appearances.

(3-4) Space is not a discursive or, as we say, universal concept of things as such; rather, it is a pure intuition.

(…) Space represents no property whatever of any things in themselves, nor does it represent things in themselves in their relation to one another. (…) Only from the human standpoint, therefore, can we speak of space, of extended beings, etc. If we depart from the subjective condition under which alone we can – viz, as far as we may be affected by objects – acquire outer intuition, then the presentation of space means nothing whatsoever. This predicate is ascribed to things only insofar as they appear to us, i.e., only insofar as they are objects of sensibility.

Immanuel Kant, The Critique of Pure Reason (1781, second edition 1787)


Different perspectives on Kant and the problem of the “Thing-in-Itself”

What is knowledge? It is above all else and essentially representation. What is representation? A very complicated physiological occurrence in an animal’s brain, whose result is the consciousness of a picture or image at that very spot. Obviously the relation of such a picture to something entirely different from the animal in whose brain it exists can only be a very indirect one. This is perhaps the simplest and most intelligible way of disclosing the deep gulf between the ideal and the real. This is one of the things of which, like the earth’s motion, we are not immediately aware; the ancients, therefore, did not notice it, just as they did not observe the earth’s motion. (…)

If, without questioning further, we stop altogether at the world as representation, then of course it is immaterial whether I declare objects to be representations in my head or phenomena that exhibit themselves in time and space, since time and space themselves are only in my head. In this sense, then, an identity of the ideal and the real might still be affirmed; yet since Kant, this would be to say nothing new. Moreover, the inner nature of things and of the phenomenal world would obviously not be exhausted in this way, but with it we should still always be only on the ideal side. The real side must be something toto genere different from the world as representation, namely that which things are in themselves; and it is this complete diversity between the ideal and the real that Kant has demonstrated most thoroughly. (…)

In consequence of all this, on the path of objective knowledge, thus starting from the representation, we shall never get beyond the representation, i.e., the phenomenon. We shall therefore remain at the outside of things; we shall never be able to penetrate into their inner nature, and investigate what they are in themselves, in other words, what they may be by themselves. So far I agree with Kant. But now, as the counterpoise to this truth, I have stressed that other truth that we are not merely the knowing subject, but that we ourselves are also among those realities or entities we require to know, that we ourselves are the thing-in-itself. Consequently, a way from within stands open to us to that real inner nature of things to which we cannot-penetrate from without. It is, so to speak, a subterranean passage, a secret alliance, which, as if by treachery, places us all at once in the fortress that could not be taken by attack from without.

Arthur Schopenhauer, The World as Will and Representation (1844).


Hume’s critique had been for Kant the death blow to metaphysics. After that there was nothing left to do but search for the cause of its death in the very nature of reason. Such an undertaking, a judgment of the validity of metaphysics’ claims, thus presupposes a certain conception of metaphysics itself. More precisely, it presupposes that metaphysics be conceived, after the manner of Descartes, Leibniz and Wolf, as an abstract rationalism devoid of all empirical content, owing its preeminent position to its perfect isolation from sensible knowledge. When Kant declares that the origin of all metaphysics’ troubles is reason’s claim to a knowledge attained “independently of all experience”, it is clear that he has forgotten the existence of a metaphysics like that of Aristotle or St. Thomas Aquinas. His formula, which applies in full to Descartes and Leibniz, leaves classical metaphysics untouched. I know quite well what objections Kant would have raised, but it is a fact that he did not take classical metaphysics into consideration. The immediate consequence of this oversight was that, instead of criticizing metaphysics, Kant criticized its two bastard offspring which the eighteenth century had bequeathed him: on the one hand a rigorous but empty rationalism, on the other hand a concrete empiricism devoid of all necessity. Having lost the notion of a rational knowledge fertilized by an intelligible datum, he had no other recourse but to deduce the intelligibility of experience from knowledge. Thus Kant was able to obtain an experiential knowledge that was both concrete and necessary, but by locating the unique source of the intelligibility of experience in knowledge he confined it within the limits of its own perfection and shut it off from any external contribution capable of fertilizing it.

(…) It might be possible to start from within the critical position in order somehow to force the knowing subject to go beyond itself and make contact with things in themselves. But here we would come in conflict not merely with the letter of the Kantian critique but with the spirit from which it was born. Kant’s critique is not content simply to ignore the question of what things-in-themselves are; it actually forbids any such question. It is of the very essence of the critical spirit to pose all questions from the point of view of the a priori conditions of knowledge and strictly to forbid all other questions. For example, the study of the conditions of knowledge must be related to two sources: sensibility and understanding. It is therefore necessary to posit both. If we ask if these two conditions of experience arise from a common source, Kant will respond: perhaps, but this source is unknown to us; there is therefore no point in spending any time trying to discover it.

(…) It is [therefore] necessary to choose between Aristotle and St. Thomas (truth is the conformity of intelligence with what is) and Kant in his logic (truth is the accord of reason with itself). Shall we judge reality as a function of knowledge or knowledge as a function of reality? That is the whole question.

Etienne Gilson, Thomist realism and the Critique of Knowledge (1939).


“Quantum mechanics introduced another point of view, which consists essentially that the aim of science is not to describe ultimate reality as it really is …Rather, it is to make account of reality as it appears to us, accounting for the limitations of our own mind and our own sensibilities … It’s not that science will explain the ultimate reality of certain objects or events … Rather, it is that the concepts we use, such as space, time, causality, and so on, … are not applicable to ultimate reality.”

Bernard D’Espagnat, quoted in Brendan Conway, “Work on ‘veiled reality’ earns French physicist $1.4 million award”, The Christian Science Monitor March 2009, (Source: http://www.csmonitor.com/USA/2009/0317/p02s04-usgn.html)


Intellectual intuition is even more immediate than sensory intuition, for it is beyond the distinction between subject and object which the latter allows to subsist; it is at once the means of knowledge and the knowledge itself, and in it subject and object are identified. (…) Knowing and being are fundamentally but one and the same thing; they are, so to speak, two inseparable aspects of a single reality, being no longer even really distinguishable in that sphere where all is “without duality” [advaita]. This in itself is enough to show how purposeless are all the various “theories of knowledge” with metaphysical pretensions which occupy such a prominent place in modern Western philosophy, sometimes even going so far, as in the case of Kant for example, as to absorb, or at least to dominate, everything else. The only reason for the existence of such theories arises from an attitude of mind shared by almost all modern philosophers and originating in the Cartesian dualism; this way of thinking consists in artificially opposing knowing and being, an opposition that is the negation of all true metaphysics.

(…) It is necessary to say something at this point about the way in which we use the word “theory”: etymologically, its primary meaning is “contemplation”, and if it is taken thus, it might be said that metaphysics in its entirety, including the realization which it implies, is theory in the fullest sense; but usage has given the word a rather different and above all a much narrower meaning. In the first place, it has become usual to oppose theory and practice, and in its original sense, this antithesis, which meant the opposition of contemplation to action, would still be justifiable here, since metaphysics is essentially beyond the sphere of action, which is the sphere of individual contingencies; but the Western mentality, being turned almost exclusively toward action and being unable to conceive of any realization outside the sphere of action, has come to oppose theory and realization in a general sense.

(…) In all doctrines that are metaphysically complete, as are those of the East, theory is invariably accompanied or followed by an effective realization, for which it merely provides the necessary basis; no realization can be embarked upon without a sufficient theoretical preparation, but theory is ordained entirely with a view to this realization as the means toward the end, and this point of view is presupposed, or at least is tacitly implied, even in the exterior expression of the doctrine.

René Guénon, General Introduction to the Study of Hindu Doctrines (1921).


One thought on “What can we know?

  1. Pingback: Introduction to Ancient and Modern Western Thought | A post-secular age

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