Immanuel Kant is said to have been woken up by Hume from his ‘dogmatic slumber’ and brought about a ‘Copernican revolution’ in the field of philosophy. In Kant we begin to reap the ripe fruits of philosophy, for it is here that it shows signs of its having reached maturity and full development.

Kant discovers that neither empiricism nor rationalism is entirely correct, though each is partially true. His problem is therefore to take stock of the previous findings in philosophy and to construct his own critical philosophy or transcendental idealism. Kant begins by saying that knowledge is not completely derived from sense-experience. We cannot confine our knowledge to the senses, as Locke and Hume supposed. Hume committed the mistake of restricting experience to separate and distinct sensations, and from this false premise came to the false conclusion that there is nothing necessary or universal in knowledge. Sense-experience gives us only probabilities and not certainties. If there is a certain, necessary and universal knowledge, it must be independent of sense-experience. The necessity and universality about such knowledge is true even prior to sense-experience,—it is a priori. We have in mathematics, for example, a knowledge which is necessary and universal; it is unaffected by what experience the senses may give us in the course of time. For never in the history of the world would an addition of seven and five cease to make twelve, and never have the principles of geometry been falsified in experience. Here is an instance of knowledge independent of sensations. Kant is here a dogmatist, for instead of asking whether synthetic judgments a priori are possible, he takes for granted that there is already such knowledge, and concerns himself with how synthetic judgments a priori are possible. He is only fired with the zeal for describing the anatomy and demonstrating the working of such knowledge, and considers, as against Hume, that to deny a necessary and universal knowledge would be a mere ‘scandal’.

Now, from where do we get such necessary and universal knowledge? Certainly not from sense-experience; for this knowledge remains independent of sense-experience. For Kant all knowledge is in the form of judgments. Genuine knowledge is a necessary and universal judgment. Sensations have nothing of the necessary or the universal in them. Hence genuine knowledge must be inherent in the very constitution of the understanding or mind itself, the very make-up of the mind, the necessary and fundamental law which determines the manner of all the functions of the mind. The mind is not a blank tablet as Locke thought, not a passive recipient of sensations, but an active agent which modifies the form of the sense-material, gives it a different shape, casts it in the mould of order, unity and method, and reorganises its constitution. So in our knowledge we have material from the senses, unity and order from the mind or the understanding. Without sensations or perceptions knowledge is empty; without thinking or understanding knowledge is blind. Kant puts his whole problem thus: How are synthetic judgments a priori possible in mathematics, physics and metaphysics? The whole of his ‘Critique of Pure Reason’ is an attempt to answer this great question.

Kant observed that sensations by themselves are subjective states and have to be referred to space and time in order to acquire the character of objectivity in knowledge. Sensations provide matter, and space and time the form. In our processes of knowledge we first organise sensations by the application of the perceptual categories of space and time, and then again organise these perceptions by the application of the conceptual categories, the pure concepts and judgments, which are twelve in number. Sensations by themselves cannot give us knowledge; they have to get themselves arranged about an object in space and time, and then we say we have the perception of an object. Without the aid of space and time there can be no perception, for sensations independently give us no knowledge of any object. Space and time are the a priori modes or ways of perception, and can also by themselves become contents of pure perception independent of objects. They are a priori, because they are the conditions necessary for the formation of sensations into perceptions. And as the laws of mathematics are the laws of space and time, they are a priori laws.

According to the empiricists, perceptions are the results of a spontaneous grouping of sensations; but to Kant this is brought about by a purpose that is detectable in the mind itself, in the sensibility of the understanding. Kant rejects the views of Locke and Hume and concludes that the understanding plays an important part in the formation of perceptions. Yet, perceptions, distinct and separated, cannot give us real knowledge. As the reformulation of sensations as perceptions is done by the application of the perceptual categories of space and time, so the perceptions are transformed into concepts by the application of the categories of the understanding. And as the sensations are grouped, arranged and united about objects in perception by means of the a priori laws of space and time, so perceptions are connected, related and organised by conceptions about the ideas of the categories of quantity, quality, relation and modality. The perceptions are cast in the moulds of these categories of the understanding and transformed into concepts and judgments. This becomes possible on account of the presence of a unifying consciousness or synthetic unity of apperception in us. The function as well as the essence of the understanding is this arrangement and organisation of sensations and perceptions. The connecting link between percepts and concepts is the time-form, which Kant calls the ‘transcendental schema’. This order, this unity in sensations and perceptions is brought about by those laws inherent in the understanding or the mind itself, and not by the sensations themselves, as Locke and Hume thought. There is a tremendous organising capacity in the mind, and this capacity is a priori, independent of sense-experience. Kant recognises that the things-in-themselves cannot be the causes of this organised character seen in knowledge, for we affirm their only by inference from the scattered sensations that we receive from outside. The capacity for order and unity has to be attributed to the mind or the understanding alone. The differences that are observed in the degrees of knowledge possessed by different persons prove that order is brought into sensations not by the sensations themselves but by the a priori laws of the mind, which is an active judge or law-giver and not a piece of wax passively receiving impressions from outside. The laws and the ordered unity of the world are therefore the laws and the ordered unity of the categories of the mind. What we call things are not things-in-themselves, but the categories of the mind alone, objectified in space and time. In other words, we see in things only the necessary and universal laws of our minds. It is the necessary and universal laws of the mind that recognise themselves in the objects of the world. Kant saves the world of physics, as he saved mathematics.

The charge that is usually levelled against Kant that he teaches naive subjectivism is not justifiable. He does not say that any particular mind prescribes its laws to Nature, but he speaks of necessary and universal knowledge which, though confined to the categories of the mind or to the manner of perceiving things, is common to the minds of all men. But he makes the laws of things the laws of the human mind, though it may be that they are of all minds. The categories of our perception and conception, he says, control all knowledge and we can know nothing beyond them. Though sensations have to be supposed to be caused by certain things-in-themselves, these latter can never become objects of our knowledge, for our knowledge is limited to the categories. Kant here is in agreement with Locke in thinking that we cannot know things as such, though they have to be conceived to be the causes of our sensations. Kant, according to the Vedanta, is not correct in supposing that the logical categories of the human mind can so modify or affect the constitution of our knowledge that we know only the logical categories and that what we call physical objects are only the objectifications of these categories of human thought. The Vedanta holds that the physical world is the manifestation of Isvara, and that the existence of objects is independent of human thinking and of its logical laws, though the human mind contributes much in determining the value of the objects by projecting on them its own desires, feelings and emotions. It may be true that certain desires, feelings and emotions are common to all mankind; yet this universality of certain psychological conditions cannot be made a factor that can affect the existence of the physical objects. Logic is not the same as metaphysics, if by logic we mean the laws of mere human thinking and reasoning. Human thinking is not a part of reality in the sense of cosmic existence. Only the mind or will of Isvara or God can have such reality and only the logic of this mind can be identical with the laws of a metaphysics of reality. And also it is only this cosmic mind that can modify the nature of the objects of knowledge by the categories or laws of its constitution. To the Vedanta the world is ideal in the sense that it is in the Idea of Isvara, but not in the idea of any man, or even in the ideas of all men. Again, space and time and the physicality and externality of the objects of the universe cannot be considered to be realities from the point of view of Isvara, for He is a spiritual Being, and the appearances of these, therefore, are to be understood as the necessary counterparts of the notion of our individual existence. The physical world has an existence independent of human thinking or willing, but it becomes dependent on thinking and willing when the human mind rises above itself and gets identified with the Mind of Isvara. Thus the existence of the physical world appears to be and has to be accepted as independent of the human mind only so long as human individuality persists, and not when it is transcended in the Cosmic Mind. Again, the existence of the world as independent of the human mind and the existence of a Cosmic Mind of which it is a manifestation and whose laws determine its nature, are necessary postulates accepted to offer a consistent and satisfactory explanation of our experiences in the world. They are relative, for they are valid only in relation to the individual, and only so long as individuality survives. The world is relative because it is dependent on the categories of space, time and causation, which have validity only in relation to the individual, and are more real than the thoughts or imaginations of the individual as long as the individual exists as such, but which are dependent on and controlled by the laws of the Cosmic Mind. To express the problem concisely: As long as an individual exists, other individuals too exist, which are as much real as itself, and there is a physical world which is as much real as all the individuals, and so not dependent on their thoughts or laws of thinking; as long as this state of affairs continues, there is to be accepted the existence of a Cosmic Mind or the thought of God, which is the author of the physical world and of all the individuals in it, and which completely determines the nature of the world with its laws, i.e., this independence of the physical world over individuals and thoughts, and this existence of the Cosmic Mind or the thought of God are necessary and unavoidable facts implied in individualistic experience. But when the individual mind is raised to the state of the Cosmic Mind, there would be neither the individual, nor the world; there would be only the Absolute-Experience. Ultimately, the world discloses its spiritual being. This explains in what way the world is independent or has extra-mental reality, in what way ideal or purely dependent on mind, in what way relative to the interaction of subject and object, and in what way non-existent. Here we see the glory of the Vedanta.

Kant recognises that though mathematics and the physical sciences are in conformity with the universal laws of thought and the system of logic, and so necessary and valid for every mind, this necessity and validity of theirs is limited to phenomena, and so they are relative. The world of sense-experience is an appearance; it does not consist of things-in-themselves, for they cannot be known, though they lie as the background of all phenomena. Some interpreters of Kant object to his assertion of the things-in-themselves as dogmatic, for when the things-in-themselves cannot be known at all, as Kant says, how can their existence be asserted? That the things-in-themselves exist, they think, is an unwarranted assumption contrary to Kant’s theory that nothing that is known is more than an appearance. Even the things-in-themselves ought to be restricted to the categories of the mind, for it is the mind that asserts their existence. Others try to save Kant from this charge by holding that his concept of things-in-themselves does not make them known as realities, but it is only a limiting concept which Kant has no objection to include within phenomena. The aim of this concept is only to point out the limits of possible knowledge or experience. But the Vedanta would go ahead of Kant as well as these critics of his and suggest to Kant himself that the things-in-themselves are not mere postulates or hypothetical suppositions as he would think, neither phenomena of the finite categories, nor even just limiting concepts, but intimations of a supermental reality, which Kant posited, even without his own knowing, through shades of a supersensuous intuition, and which he, by analogy from physical objects of perception, wrongly supposed to be many in number. Really there is only one Thing-in-Itself, the Eternal Spiritual Being, and not many things-in-themselves. Sometimes Kant even gives us a hint that the things-in-themselves are material objects, though their exact nature cannot be known by us, which would obviously be a lapse into the Lockian theory of representationism. How can we say that the objects are material when they are not known? Kant cannot make himself consistent unless he admits the thing-in-itself to be a spiritual essence, indivisible, and so infinite or non-dual.