Kant is understood against the historical background in which the two main currents of thought were Cartesian rationalism and Lockean empiricism. The former took mathematics as paradigmatic for a priori knowledge and certainty; the latter was concerned about the process by which gathering sense-data into perceptions could be formalized into something like the modern observational sciences. In opposition to each other, the philosophers had to then choose either to embrace metaphysical certainty at the cost of reliable knowledge of the perceivable world, or to embrace observational realities at the cost of any other form of reality. Dinesh D’Souza notes, regarding the latter view especially, that empiricists
may not recognize it, but there is a huge assumption being made here. These men simply presume that their rational, scientific approach gives them full access to external reality.
Which is to say, having sacrificed Cartesian metaphysics for the sake of empirical natural sciences, they may find that they have gotten a bad deal: this scientific method may not yield as much as they had hoped. Isaac Newton, after, warned against framing hypotheses - a foreshadowing perhaps of Kant’s more thorough critique. Whether through a naive direct realism, or a more nuanced indirect realism, or even a radical empiricism, a claim is made about the mind’s ability to gather information about the world.
Before Kant, most people simply assumed that our reason and our senses give us access to external reality — the world out there — and that there is only one limit to what human beings can know That limit is reality itself. In this view, still widely held by many in our society, human beings can use the tools of reason and science to continually find out more and more until eventually there is nothing else to discover. The Enlightenment fallacy holds that human reason and science can, in principle, gain access to and eventually comprehend the whole of reality.
Kant’s Critique of Pure Reason was published in 1781, and urged a humility in making claims about what human reason can discover.
In fact, he argues, there is a much greater limit to what human beings can know. In other words, human reason raises questions that — such is the nature of our reason — it is incapable of answering. And it is of the highest importance that we turn reason on itself and discover what those limits are. It is foolishly dogmatic to go around asserting claims based on reason without investing what kinds of claims reason is capable of adjudicating. Reason, in order to be reasonable, must investigate its own parameters.
It is human nature to ask questions. We will ask many more questions than our reason can answer. We therefore can create two categories of questions: those answerable by human reason, and those not. If a question cannot be answered by human reason, we might then go on to ask whether it can be answered at all - and if so, how.
Kant begins with a simple premise: all human knowledge is based on experience. We gain access to reality through our five senses. This sensory input is then processed through our brains and central nervous systems. Think about it: every thought, even the wildest products of our imagination, are exclusively based on things that we have seen, heard, touched, smelled, or tasted. If we imagine and draw creatures from outer space, we can give them four eyes and ten legs, but ultimately we have no way to conceive or portray them except in terms of our human experience. It is an empirical fact that our five senses are our only lenses for perceiving reality.
More accurately, Kant writes that all knowledge begins with experience. Even that knowledge which has no basis in experience (Cartesian a priori mathematical certainties) arises in the course of experience. So we all knowledge begins with experience, but some knowledge is based on experience.
Now Kant asks a startling question: how do we know that our human perception of reality corresponds to reality itself? Most philosophers before Kant had simply taken for granted that it does, and this belief persists today. So powerful is this “common sense” that many people become impatient, even indignant, when Kant’s question is put to them. They act as if the question is a kind of skeptical ploy, like asking people to prove that they really exist. But Kant was no skeptic: he saw himself as providing a refutation of skepticism. He knew, however, that to answer skepticism one has to take the skeptical argument seriously. The way to overcome skepticism is by doing justice to the truth embodied in it. Kant’s goal was to erect a dependable edifice for knowledge on the foundation of extreme skepticism.
Like Descartes, Kant finds a constructive use for skepticism. Like Hume, Kant asks if we have any justification for positing whatever ontology we may embrace. Unlike Thomas Reid, Kant denied that common sense provided enough justification.
Kant’s question about the reliability of human perception has been the central preoccupation of Western philosophy since Descartes. How do we know what we claim to know? Locke had famously pointed out that material objects seem to have two kinds of properties, what he called primary properties and secondary properties. Primary properties are in the thing itself, whereas secondary properties are in us. So when we perceive an apple, for example, its mass and shape are part of the apple itself. But Locke ingeniously pointed out that the redness of the apple, its aroma, and its taste are not in the apple. They are in the person who sees and smells and bites into the apple. What this means is that our knowledge of external reality comes to us from two sources: the external object and our internal apparatus of perception. Reality does not come directly to us but is “filtered” through a lens that we ourselves provide.
Kant writes to the effect that the human mind provides a great deal of structure to what we perceive as reality. The structuring process begins with space and time - two products of the mind. What we naively perceive as one object’s being “there and then” and another object’s being “here and now” is merely our five senses importing information about the world, but rather largely a creation of our mind. Methodically internalizing the notion that time and space are not facts about the world, but tools created by our mind for the purpose of organizing sense-data, will change our assessment of observational natural sciences regarding their ability to give us information about the world.
Philosopher George Berkeley radicalized this mode of inquiry: “When we do our utmost to conceive the existence of external bodies, we are all the while only contemplating our own ideas.” Berkeley’s argument was that we have no experience of material objects that exist outside the perceptual apparatus of our mind and senses. Both the primary and the secondary qualities of objects are perceived in this way. We don’t experience the ocean, we experience only our image and sound and feel of the ocean. Berkeley famously concluded that we have no warrant for believing in a material reality existing independent of our minds!
Although Berkeley’s idealism can be seen as the organic consequence of the epistemology of his era, it would seem to Kant to be perhaps equally unwarranted: positing the existence of physical objects in the world requires justification just as much as positing the lack of their existence.
Hume completed Berkeley’s skeptical argument by applying it to human beings themselves. We have no experience of ourselves other than our sensations and feelings and thoughts. While we know that sensations and feelings and thoughts exist, we have no basis for postulating some “I” behind them that is supposed to be having those reactions.
Hume’s radical empiricism, while a direct descendant of Locke’s thought, took the matter to this arresting extreme. Berkeley had denied the existence of a material external world; Hume denied the existence of a self or perceiving mind. All that remained, then, was a collection of sensations, corresponding to no objects, and perceived by no subject.
Kant conceded Berkeley’s and Hume’s point that it is simply irrational to presume that our experience of reality corresponds to reality itself. There are things in themselves — what Kant called the noumenon — and of them we can know nothing. What we can know is our experience of those things, what Kant called the phenomenon.
At first blush, Kant is saying that not only can we not know what the external world is like, but also that we cannot even know if it exists. He embraces the extremes of Berkeley and Hume, but only as a starting-point: the constructive use of skepticism.
Our senses place absolute limits on what reality is available to us. Moreover, the reality we apprehend is not reality in itself. It is merely our experience or “take” on reality. Kant’s point has been widely misunderstood. Many people think that Kant is making the pedestrian claim that our senses give us an imperfect facsimile or a rough approximation of reality.
Not only would Kant claim that our sense limit what we can know, but also that the structure of the human mind limits knowledge as well. We can, for example, know or imagine only objects in space and time, and only in our particular type of space and time. It is important to understand what Kant is not writing: he is not dealing with, for example, the limitations on eyesight, that we can’t see further away, or with more magnification, or beyond the spectrum of visible light. That’s not his point - those are mere differences of degree. He is speaking about differences of kind - knowledge which is not only impossible for us to gain, but which is in principle impossible.
Kant’s argument is that we have no basis to assume that our perception of reality ever resembles reality itself. Our experience of things can never penetrate to things as they really are. That reality remains permanently hidden to us. To see the force of Kant’s point, ask yourself this question: how can you know that your experience of reality is in any way “like” reality itself? Normally we answer this question by considering the two things separately. I can tell if my daughter’s portrait of her teacher looks like her teacher by placing the portrait alongside the person and comparing the two. I establish verisimilitude by the degree to which the copy conforms to the original. Kant points out, however, that we can never compare our experience of reality to reality itself. All we have is the experience, and that’s all we can ever have. We only have the copies, but we never have the originals. Moreover, the copies come to us through the medium of our senses, while the originals exist independently of our means of perceiving them. So we have no basis for inferring that the two are even comparable, and when we presume that our experience corresponds to reality, we are making an unjustified leap. We have absolutely no way to know this.
What we know, then, as the laws of chemistry or physics, are actually psychological laws about the functioning of the mind. Given that I know only my perception of atoms or stars, the laws which I think regulate atoms and stars actually regulate only my perceptions of atoms and stars.
It is essential, at this point, to recognize that Kant is not diminishing the importance of experience or of the phenomenal world. That world is very important, if only because it is all we have access to. It constitutes the entirety of our human experience and is, consequently, of vital significance for us. It is entirely rational for us to believe in this phenomenal world, and to use science and reason to discover its operating principles. A recognized scientist and mathematician, Kant did not degrade the value of science. But he believed science should be understood as applying to the world of phenomena rather than to the noumenal or “other” world.
We understand that Kant is not denying the existence of an external world - he pointed out that we have no justification for denying its existence - but rather he is demonstrating the inability of reason to know about that world. Kant ultimately disagrees with Berkeley. Nor is he saying that we can know nothing about the external world - he is saying that our reason can know nothing about it. He leaves the door open for other types of knowledge.
For Kant, the noumenon obviously exists because it gives rise to the phenomena we experience. In other words, our experience is an experience of something. Moreover, Kant contends that there are certain facts about the world—such as morality and free will—that cannot be understood without postulating a noumenal realm. Perhaps the best way to understand this is to see Kant as positing two kinds of reality: the reality that we experience and reality itself. The important thing is not to establish which is more real, but to recognize that human reason operates only in the phenomenal domain of experience. We can know that the noumenal realm exists, but beyond that we can know nothing about it. Human reason can never grasp reality itself.
The warning is worth repeating, however, we have not yet looked directly at the texts written by Kant; we have here quoted from a summary written by Dinesh D’Souza, who teaches at Stanford University. We have, in fact, seen that his summary needs a few small correctives along the way. This is the perpetual problem confronting those who would produce an accessible and popular explanation of a philosopher’s works: Kant’s text are hundreds of pages long, written with bizarre neologisms and interminable sentences. It is necessary to produce some type of popular summary, because these books will be forever inaccessible to some readers; yet while it is necessary to do so, it is also to some extent impossible.
