An Introduction to Kant’s Critique of Pure Reason

Immanuel Kant is an 18th century philosopher, belonging to the era of the Enlightenment. The Enlightenment is an intellectual epoch where reason triumphed over faith. Kant is arguably one of the greatest intellectuals of all time, and his Critique of Pure Reason is considered his magnum opus. It was published when he was 57, so he had a whole lifetime to meditate upon the nature of reason. So don’t expect the book to be an easy read. It is precisely for this reason that an introduction to it can be helpful, to understand what his project is about and its broad strokes.

Kant wrote Critique to enquire into the nature of reason, laying the path for that by first examining how we perceive and understand things. Perception

So how do we perceive things?

One theory, not Kant’s, would be that we have a direct perception of things through our senses. Say there is an apple in front of us. We use our eyes to look at it. Light rays reflected off the apple impinge on our eyes, and so we perceive an apple, through a direct comprehension of the sense data. An empiricist, who believes that everything we know, we know through our sense experience, might agree with such an account.

Kant’s theory is however more subtle. The first steps are the same as the empiricist. Light rays reflected off the apple impinge on our sense organ, in this case our eyes. But for us to perceive it as an apple, our minds need to interpret that raw sense data. Otherwise, all that is perceived is raw sense data which will not make any sense to us. The machinery that does the interpretation are our mental faculties. There are 3 mental faculties – the faculty of sensibility, the faculty of understanding and the faculty of reasoning.

These faculties have within them certain structures to carry out their functions. For the faculty of sensibility, to make sense of the raw sense data, it needs to have a background structure of space and time.



Space

In a world with many objects, we need to differentiate between the different objects. Imagine if it is just raw sense data. So for a red apple with a green pear in front of it, the eyes will get a 2D image of a red shape with a green shape on top of it. We may then mistakenly perceive it as 1 unified object.

How then do we know it is actually 2 separate objects? It is because we have this form or structure of space in our minds. We have this concept of space such that we know we have 2 different objects because they occupy different spaces. Say now it is 2 identical looking apples. We can still tell them apart because despite all their similarities, they are occupying different spaces.

And while our sense organ, the eyes, can only give us 2-dimensional images, yet we perceive 3-dimensional objects. Our retinas cannot give us depth information. If we look at a pencil from the rubber end head-on, what we would see is a flat circle. We cannot tell how long the pencil is. However, when we rotate the object, or we move our heads, we get some more images. Somehow, we join or synthesise these images together to give us the 3D image of the pencil. So our minds is doing some work, it is not just perceiving raw sense data. This work requires that we have the concept of space already a priori in our minds. What a priori means is that before we receive any sense data, any information from the world, we already have the concept of space in our minds, because otherwise, we cannot perceive any objects. A prori also means it is necessary and universal for all minds to have this concept of space.



Time

How about changes?

Say there was an ice cube on the table at 4pm. Then at 5pm, we see a puddle of water at that same spot on that table. If it was only raw sense data that we perceive, all we can say is, there was this ice cube. Then we later say, there was a puddle of water, but we have no way of connecting them to each other. They will just be 2 different objects. But yet we do make the connection between them, to say that they are the same object, just having a different quality, for 2 reasons according to Kant.

The first is that we have the a priori concept of time in our minds. This structure of time is there in our minds, which then informs changes that we perceive. The second is that we have this concept of cause and effect, which links the cause of the puddle of water with the ice cube receiving heat from its environment.



Transcendental Philosophy

Before I move on to discuss the concept of cause and effect, let’s close this bit on space and time. Kant calls this a priori intuitions of space and time in our faculty of sensibility the transcendental aesthetic. It is called transcendental because it is what is required for our perception above or before we manage to perceive anything, even before we receive the sense data. It is a pre-condition, it is a priori. Time and space are mental constructs, called forms or structures, that we must have to be able to perceive objects in the world.

This transcendental aesthetic is one of 3 parts of his transcendental philosophy. The transcendental aesthetic deals with perception and its conclusion is that space and time are a priori forms of intuition in our faculty of sensibility. There are 2 other parts of Kant’s transcendental philosophy. They are the transcendental analytic, which deals with the requirements of our minds to have understanding. Understanding something is to make correct judgements on that thing and we do so through concepts. The last part of the transcendental philosophy is the transcendental dialectic, which deals with the requirements of our minds to be able to reason about things. To reason is to have ideas.



Transcendental Analytic

I will now talk about the transcendental analytic, which is about our understanding and so I go back to the cause and effect when we were talking about the ice cube becoming water.

Before Kant came onto the scene, David Hume had said that there is no such thing as cause and effect. When the first billiard ball knocks into the next billiard ball which was stationary, the next billiard ball moves. You would say that the first ball was the cause of the 2nd ball’s motion right? Not Hume. He asked, where do you see causation? All we had seen was “constant conjunction.” It was the 1st ball knocking the 2nd ball and the 2nd ball moving.

When we strike a bell, we hear a sound. Constant conjunction. We do it multiple times, we’d learn to associate that sound with the bell being hit. We experience one event following closely on the heels of an earlier event. We learn to associate them together, as a habit. And out of convention, we call the first event the cause and the second one the effect. But nowhere do we see ever see causation, according to Hume.

Hume is an empiricist. Empiricists believe that all knowledge come only from sense experience. There is no other source that can give us knowledge. So since we don’t directly experience causation, there is no such thing as causation. All that we have to deal with what seems like causation conceptually is association.

Kant read this and he said that Hume woke him out of his “dogmatic slumber.” Kant, like most of us, had bought into this dogma of cause and effect. The challenge Hume presented was one of the triggers for Kant to think about the nature of our reason, our understanding and our perception of reality.

How Kant explains causality is, cause and effect is a concept that we need, among other concepts which he called categories, to understand things, to make judgement about things. To make sense of events, we need some structures in our minds prior to the perception of the event, ie. a priori concepts. Cause and effect is 1 of these 12 categories which he grouped under ‘relations’.

Another is the category of affirmation and negation. Say you see a chair. You say: ‘This is a chair.’ You are affirming that there is a chair there. But to be able to affirm, you must also be able to deny the existence of the chair, to negate your statement. You might realise later, ‘No, this is not a chair, this is a table,’ which you had somehow mistaken for a chair. So, we get 2 categories of affirmation and negation.

Another is the category of unity and plurality. To be able to understand the concept of 1 chair, you must be able to understand also 2 chairs, or 10 chairs etc, and differentiate them numerically. So here are 2 more categories, unity and plurality, which he grouped under ‘quantity’.

There are 4 groups, each of which has 3 categories adding up to a total of 12 categories. I won’t go through them all, but the idea of the categories is that to understand things, to make judgements about things, we need these categories so that we can think through what is happening and make sense of it. This part of Kant’s transcendental philosophy, he calls the transcendental analytic.



Phenomena and Noumena

Before moving to the final part of his transcendental philosophy, the transcendental dialectic which concerns our reason, let’s talk about “appearances” and “presentations.” Kant says that all that we perceive, all that we understand, about objects in the world are mediated through our minds. We never perceive and understand the thing-in-itself, whose technical name is “noumena.” All we perceive and understand are the appearance of things, are the presentations we make of things, which are mediated through our minds or consciousness. The technical term for these appearances of objects and events are called “phenomena.”

For instance, space and time are forms, are structures, in our minds; we do not know and cannot know if space and time actually exist in reality, in the objects themselves. All we can know is the phenomena, not the noumena.



Transcendental Unity of Apperception

To pave the way to talk about the transcendental dialectic and reason, let’s deal with what Kant calls the Transcendental Unity of Apperception.

The concepts in the transcendental aesthetic and the transcendental analytic are related to each other. The forms of space and time, which belong to the transcendental aesthetic, are related for example to the categories of unity, plurality and causality, which belong to the transcendental analytic. We talked about distinguishing one object from another by recognising that they occupy different spaces. This involves the category of unity and plurality. We talked about the ice cube which became later the water puddle. The water puddle was there later in time, but we know it is the same object as the ice cube because of the category of causality.

How do we know however that all these appearances are not just figments of our imagination? We already said that we have no access to the thing-in-themselves, to the noumena. Otherwise, we would compare the appearances with the thing-in-themselves. But we are unable to do that.

How we know that the appearances we perceive are of real things is because they fit with our concepts, they follow categorial principles, ie. they follow the rules of the categories. For example, the melting of the ice cube to form a water puddle fits into the causal structure of the world. The chair you perceived remained there even when you stopped thinking about it, when you turned away from it and then turned back to it, in accordance with the category of substance which we didn’t elaborate on. While if you had merely imagined the chair, once you stopped imagining the chair, it would no longer be there.

So, what is this Transcendental Unity of Apperception? Apperception is the technical term for our self-consciousness, ie. we are aware of our own existence and that we have minds. Our sense of self does not come from our senses. Imagine if you are born deaf, blind, have no sense of touch, taste or smell. Would you agree that you would still be self-aware? Our self-awareness is a priori. Our mind is unified, meaning that there is a synthesis of our concepts, ie. of the forms of space and time and the 12 categories, and we can draw many of our cognitions into one. It is transcendental because once again, these concepts are a priori.



Transcendental Dialectic

Now we are ready to talk about the transcendental dialectic which concerns our capacity to reason. To Kant, when we reason, we are reasoning about the conditions of our ability to understand.

We perceive and understand appearances, and these appearances are appearances of things. These perceptions and understanding constitute our knowledge. But our knowledge is knowledge of appearances, not of the things-in-themselves. Just because to perceive things, we need the forms of space and time, doesn’t mean space and time exist objectively, that they exist in reality. To rephrase, we have an epistemological need for space and time, but that doesn’t mean that they are real, that we can make the metaphysical conclusion that space and time exist. Epistemology is the theory of knowledge, while metaphysics is the theory of the nature of reality. To have knowledge, we need space and time as concepts, but that don’t mean space and time exist in reality. We do not know the noumena.

Reasoning is our ability to make inferences. Let us consider an inference, which is Kant’s own example. The inference is about how a man named Caius is mortal. To make such an inference, we draw on the concept of man, who is mortal. To make such an inference that man is mortal, we draw on a higher principle, say of mammals which are mortal. And so on. We move up the chain of species and genuses, reaching the genus of animals, and draw on the principle, that all animals are mortal. We can go further still, to the genus of living things. So our concepts are related to each other in a hierarchy, of higher-level principles to lower-level ones. We are making an ascending series of inferences in our reasoning.

Let us make another. We observe that a particular event is caused by a preceding event. We infer that that earlier event was caused by yet another earlier event. Our reason will suggest that there is a whole chain of causes and effects leading all the way back to what must be the first cause, which must itself be uncaused because otherwise we would have an infinite regression. To help us understand our world, there seems to be a need for this first cause. This line of thought is known as the cosmological argument for the existence of God.

To understand our world, our minds need the world to be orderly so that we can then have a systematic understanding of it. This is what our reason suggests to us. But just because our reason suggests a need for a first cause and a need for nature to be orderly, doesn’t mean that indeed there is a first cause or that nature is orderly. We cannot go from our epistemological needs to make metaphysical conclusions. Our principles of reasoning are regulative, not constitutive. This idea of orderliness of nature and this idea of a first cause help our understanding but don’t make them real.



Antinomies

To further explicate reason, Kant talks about antinomies. An antinomy is a conflict between two claims which contradict each other yet can be argued for equally well. For instance, the question of free will versus determinism is an antinomy. Because every event requires a previous event to cause it, it leads to a chain of causes and effects, making all events determined. Yet for morality to exist, we need to be agents with free will, and not just have everything already pre-determined.

Kant resolves this conflict by pointing to the limits of our knowledge based on his transcendental philosophy. That things stand in causal relations to one another is a requirement of our understanding of appearances in the transcendental analytic, but it does not tell us about how things are in reality since we cannot know thing-in-themselves. He doesn’t however take on an agnostic position. He says that while theory cannot help us here, practical considerations can. To live well, we have to live morally and so we need free will for us to live ethically. He is opening the door for religious beliefs, which he says cannot be based on theory due to the limitations of our reason but is a matter of faith.



Conclusion

To conclude:

± All knowledge is a product of sensory evidence + the mind’s own principles for dealing with the evidence.

± Hence there are limits to our knowledge.

± Our standards for truth are internal, and depend on the structure of our cognition, which are space and time, which belongs to the transcendental aesthetic, and the 12 categories which belongs to the transcendental analytic.

± We cannot know the noumena but only the phenomena which interprets the noumena through the structure of our cognition.

± To go from epistemological requirements to metaphysical truth is an invalid move.

± Some things are hence not knowable but we can still function based on practical considerations.



Concluding Remarks

A concluding remark of my own is that the Critique of Pure Reason is a difficult book. Kant writes very well, some parts of the Critique are even poetic, and he illustrates his ideas with illuminating examples, but the topic is difficult since he is thinking about how we think which is so fundamental that the ideas put forward can seem rather obtuse and counter-intuitive.

He also argues it rather thoroughly, which means he argues his opponent’s case as well, which can be hard to follow since those arguments go against our common understanding. The reason why I decided to present an introduction to the Critique is because when I myself was introduced to it in a lecture, it really helped me understand what his big ideas are, what his project is about, which then helped a lot in my understanding of his ideas and the book, which is a landmark in the history of philosophy.

If you do intend to read the book, the version I read was the 1996 edition translated by Werner S. Pluhar, which has an excellent introduction by Patricia Kitcher, who is currently professor of philosophy at Columbia University. I recommend you read her introduction. My introduction is like a simplified version of her introduction. Her introduction is like a simplified version of the book. Going up the ladder of difficulty in such a way is not a bad approach to a complex and long book, around 800 pages, like Kant’s Critique.