Dr Tom Kerns
North Seattle Community College



Introduction to Immanuel Kant


The Critique of Pure Reason (1781)
Prolegomena to Any Future Metaphysic (1785)

(This lecture is another longish one; you may want to print it for easier reading)
(A very short outline of parts of this lecture is available here)

If one had to list the eight or ten most influential thinkers in the past 2500 years, Immanuel Kant's name would almost certainly be on that list.

Kant's writings are deeply profound, difficult to understand, and rich with complexities. In graduate school I took a full course on Immanuel Kant. Graduate courses presumably cover more material than undergraduate courses and yet this course covered only one thinker. In that entire course we read only one of Kant's books, The Critique of Pure Reason, a rich and difficult book, and in that entire course we got through less than half of The Critique. The reason is that it takes a great deal of time and effort to work through and understand the philosophy of Immanuel Kant. The effort expended in understanding Kant is, however, immensely worth it. (For a well-written summary of Kant's metaphysic, you might also read Schopenhauer's excellent eight-page summary of Kant which he adds as an appendix at the end of The World as Will and Representation, pp 417-25.)

In this introductory course, however, we will look at only two of Kant's many ideas, and we are going to look at these two because understanding them is an important prerequisite to understanding the writings of Arthur Schopenhauer. Both of these ideas derive from Kant's analysis of the rationalist and empiricist philosophers who immediately preceded him. (See the historical/philosphical map.) The two ideas we will examine in this lecture are, in this order, 1) Kant's big question, and 2) the categories of perception.

I. The Big Question:

The big question is, stated simply, "Is it possible to know what is ultimately real?" Or "Is metaphysics even possible?" (Metaphysics, for our purposes here, is the discipline which attempts to understand the ultimate nature of being, i.e., which tries to know what is really and ultimately real.) This question is not a particularly new one, but Kant's phrasing of the question turns out to be what is significant. He asks the question in this way: "Are synthetic, a priori judgments about noumena possible?" In order to understand what this question is asking, we will need to look at some of the unfamiliar words in it.

a. phenomenal and noumenal

Let's begin with the word noumena, plural of noumenon. This distinction between phenomenon and noumenon is basically the same as the distinction between appearance and reality. The phenomenal and the noumenal are two aspects of The Real, viz., the aspect which appears to us when we perceive it, and the aspect that is actually really real. The physicists, for example, tell us that even though the chair appears to be impenetrable and solid, in fact it is made up of molecules and atoms which are themselves made almost entirely of empty space. So the way a thing appears to our senses may not be, at least according to physics, the same as the way the thing really actually is. The phenomenal aspect of a thing may be entirely different than the noumenal thing, the thing as it really truly is.

Thus, phenomenon and noumenon are thus two aspects of the real, as in this little chart:

 Aspects of the Real



And Kant's question is asking whether it is possible to know the noumenal aspect of things. It is obviously possible to know the phenomenal aspect of things, because the phenomenal is what shows, it is what appears to us ("phenomenon" is from the Greek word which means "to show"). But the question before us is whether it is also possible to know what is really real. Berkeley claimed that the only things that were really real were perceptions and minds, and Hume believed that everything we experience is really only a perception, and that what we think of as our self or identity is not really real at all.

So is it even possible to know what's really real? That is what Kant is asking.

b. a posteriori and a priori

Let's next consider the terms a priori and a posteriori.

 Ways of Knowing

a posteriori

a priori

As the chart above indicates, a posteriori and a priori are two ways of knowing. Experiential, or a posteriori, knowing is knowing based on experience, i.e., knowledge that is logically posterior to (and grounded in) experience. It is empirical knowledge, therefore, and derives from our experience.

Experiential knowledge, of course, can give us knowledge only of appearances, since our experience shows us only how things appear to our experience. So a posteriori knowledge can give us knowledge only of the phenomenal aspect of things, never of the noumenal.

What this means is that if we are ever to have knowledge of the noumenal, of what is really real, that knowledge will have to be based on some non-a posteriori kind of knowledge. Kant calls such knowledge (if there is any such thing) a priori knowledge because it is not based on experience, i.e., is logically prior to experience. In other words, if we are to have knowledge of the noumenal, it will have to come from some form of a priori knowledge because a posteriori knowledge gives us only knowledge of how things appear (phenomenally) to our senses.

So Kant's question is thus asking whether it is possible to have a priori knowledge of the noumenal.

Now does any such thing as a priori knowledge even exist, i.e., knowledge that is not logically grounded in experience? Kant thinks that there is at least one example of a priori knowledge, and that is mathematics. We do not learn about square roots and decimals, Kant thinks, by looking around in the world. We do not find such things in the world. Knowledge of these things is not based in our experience of the world, but is based instead on some non-experiential grounding. Whether Kant is correct in this claim about mathematics is almost irrelevant for our purposes, though (some mathematicians agree with him and some don't). Because whether he is right or wrong about mathematics, his big question still requires that in order to know what is really real, beneath the appearances, we will need to come to knowledge of that noumenal reality by means of some kind of non-empirical a priori knowledge.

So Kant's question is thus asking whether a priori knowledge of the noumenal is even possible.

c. synthetic and analytic statements

And finally, as in the chart below, there are two basic kinds of propositions or statements, synthetic propositions and analytic propositions.

 Kinds of Propositions



Every proposition has basically two terms in it, arranged in the same basic form: Subject is Predicate. An example of a standard proposition would be "The ball is red." What this proposition is proposing is that these two terms, ball and red, should be thought of as going together. When you tell me that the ball is red you are asking me to put two quite different concepts together. You are proposing that I synthesize - put together - two different concepts, ball and red. "The ball is red" is considered a synthetic proposition because it is proposing that I synthesize two quite different concepts.

An analytic proposition, on the other hand, is quite different than this. Consider the proposition "A bachelor is an unmarried male" (this is actually Kant's own example; he was a bachelor all his life). Notice the two concepts in this proposition, "bachelor" and "unmarried male." Those are not two different concepts at all, but in fact are exactly the same concept just expressed in two different ways. So when someone says "A bachelor is an unmarried male" you learn absolutely nothing new. You've heard only a tautology. You've heard a proposition that simply analyzes the concept of "bachelor," which is why it is called an analytic proposition.

In the same way we could create an analytic proposition about noumenal reality. For example, we could say "The noumenal is what is really real." Again, the two concepts in that proposition, "noumenal" and "really real" are the same exact concept just expressed in two different ways. So that proposition doesn't tell you diddly squat about what noumenal reality is, and for that reason it's really pretty useless as a proposition.

So Kant's question, therefore, is asking whether synthetic a priori propositions about noumena are possible. Or translated it could read thus: is it possible to have real knowledge about what is ultimately really real, and that knowledge cannot be based on experience since experience gives us knowledge only of appearances?

That's Kant's question, and his manner of asking it is more important than any answers he may have attempted himself.

Post-Kantian philosophers have answered the question in various ways, as you can see by consulting the philosophical map I've put together for you. Our interest will be primarily in Schopenhauer's answer to this question, because out of Schopenhauer's thought comes much of what is interesting in Western thought ever since then (as you will see on the philosophical map).

II. The Categories of Perception

You recall the little binary computers discussing whether the world out there really is made up of only ones and zeroes? They thought it must be because everything they experience actually is in the form of ones and zeros. However, the real reason they experience the world that way is because those are the only two categories their processors are capable of recognizing.

Immanuel Kant believes that we humans have more categories of perception than the binary computers have, but that we still perceive everything in terms of our particular categories because our minds can register only what our minds are capable of registering.

a.) Let's consider time, one of the primary categories that Kant believes shapes all our perceptions, just as ones and zeroes shape the perceptions of binary computers. (The category of time includes such notions as now and then, earlier and later, before and after, fast and slow, duration, and so on.) Time shapes all our perceptions because our minds are simply incapable of having any perceptions except those that are conditioned by time. We are, of course, capable of having perceptions in which time acts in some very strange and unusual ways. For example, in Kurt Vonnegut's Slaughterhouse Five, the author tells us that "Billy Pilgrim came unstuck in time." He sometimes was living in the 1950s or 60s, and other times was in the midst of World War II in Germany. And we've all experienced time as seeming to slow down or speed up, but none of us, says Kant, has ever had an experience that is not conditioned by time.

This fact alone, viz., that every single actual experience we have ever had, without exception, has occurred in time, ought to make us suspicious that time is a human construct, something our minds must add to experience in order for the experience even to register with us. (As the bumper sticker says: Time is the mind's way of arranging things so that everything doesn't happen all at once.) So the fact that the entirety of our actual experience occurs in time ought to make us suspicious that time is something in us rather than out in the world.

But even more important, our minds are incapable of even imagining what a time-less experience would be like. The fact that we cannot even imagine a non-time-conditioned perception ought to make us even more suspicious that time is a condition our minds add to perceptions. The way Kant says it is this: the fact that all of our actual and all of our possible experience is conditioned by time is an indication that time is one of the mind's necessary categories of perception.

b.) The situation is similar with regard to the concept of space. Space conditions every experience we have ever had. (Space includes notions such as here and there, large and small, near and far, up and down, high and low, around, proximity, and so forth.) The fact that every actual experience we have ever had has been conditioned by space ought to make us suspicious that space is a human construct, something our minds must add to experience in order for it even to register with us. (I've never seen a bumper sticker that says this, but there should be one: Space is the mind's way of arranging things so that everything doesn't happen all in the same place.)

But even more important, our minds are simply incapable of even imagining what a space-less experience would be like. The fact that we cannot even imagine a non-space-conditioned perception ought to make us even more suspicious that space is a condition our minds add to perceptions. The way Kant says it is this: the fact that all of our actual and all or our possible experience is conditioned by space is an indication that space is one of the mind's necessary categories of perception.

Kant considers space and time to be the two primary conditioners of all our experience, the two "transcendental forms of perception."

 Transcendental Forms of Perception



But in addition to these two transcendental forms of perception, twelve other categories also condition our experience.

In the following table you can see what those other categories are. We will not spend time on these other categories except to single out the middle one under Relation: viz., cause and effect.

The Categories of Perception

 Of Quantity

 Of Quality

 Of Relation

Of Modality 



Inherence and Subsistence 

Possibility - Impossibility 



 Causality and Dependence (cause & effect)

 Existence - Non-existence



 Community (reciprocity between agent & patient)

 Necessity - Contingence

You will recall that Kant had said that reading Hume woke him from his "dogmatic slumbers." He fully agreed with Hume's discovery that we never directly experience cause and effect. That is, we never experience the actual causing happening, but instead experience only the regular contiguity of two events that are juxtaposed with each other in time (e.g., flipping the switch up, and then seeing the light go on). Kant says that Hume was right about that: we do not experience causing. But we human beings do need to think in terms of cause and effect because it is simply one of the categories of our mind. Just as binary computers think in terms of ones and zeroes, so we think in terms of space, time, cause and effect, etc. It's just the way we're built, says Kant.

In any case, what this all means for Kant is that our entire experienced world, i.e., our entire phenomenal world as it appears to us in our daily experience, is conditioned by space and time, by cause and effect, and by all the other eleven categories of our minds.

We can thus say that the whole multiplicity of the phenomenal world - what Buddhism refers to as the ten thousand things - is "the temporal, spatial, causal manifold."

This phrase -- "the temporal, spatial, causal manifold" -- becomes significant in Schopenhauer's thought, because he pretty much buys most of what Kant says here about the categories of perception.. So the question for Schopenhauer becomes, is it possible for us to know what is ultimately real beyond the appearances, beyond the temporal, spatial, causal many-fold multiplicity of our experience?

Schopenhauer believes the answer to this question is yes it is possible, and that the ultimate noumenal reality which lies behind all the appearances is, as you will see in reading him, Der Wille.