I shall now move on to a discussion of Immanuel Kant, who to some extent was responding to Hume's skepticism. Indeed, Hume's attack on the rationality of belief is just a symptom of an overall failure of philosophy to carry out its mission. Philosophy indulges in metaphysics, an attempt to gain knowledge of things that completely outstrip what pertains to human sense experience. Philosophers try, for example, to prove the existence of a God who is separate from the sensible world. They try to prove the immortality of the soul, its existence beyond life, and so forth. But they always fail, falling into futile squabbling which can never be resolved.
Kant recognized two ways in which metaphysics can be conducted. The way of Plato and Descartes relies on rational or intellectual intuition. We know things beyond this world through a mental vision which "sees" these things in its own way. Kant simply dismissed this approach as mystical. It does not rely on arguments but on an experience that cannot be communicated.
A more plausible approach is that of Aristotle, as exemplified in his proof of the existence of God, the unmoved mover. Aristotle appealed to phenomena of the sensible world, the motions of things on earth and in the heavens, and then jumped to an intelligible world to locate the cause of the motion of what is seen. He did so in order to obtain completeness. Unless there is a condition of motion which is not itself subject to any condition (a mover which is not moved), there can be no rest for the intellect in its search for understanding. This approach, even if it is wrong, is in the form of an argument and subject to rational criticism.
Where does this approach go wrong? Kant proposed that its error lies in seeking for an object to conform to our concepts. Thus if seek to understand motion, we form the concept of an unmoved mover. Then we say that there must be an object to correspond to that concept. We gain knowledge of that object through our argumentation, but we believe that it was there (so to speak) waiting to be discovered.
Kant thought that to make progress, we might have to turn this picture upside down, just as Copernicus had reversed the way we look at the motions of the heavens. Rather than seeking objects to fit our concepts, we should investigate whether it our concepts which determine what an object is. That is, for anything to be an object for human representation, it must conform to concepts we bring to the object.
But this just raises a further question: how could objects be tied down by the concepts we have of them, by the way we represent them? The first step toward an answer is to limit the range of these special concepts. Thus Kant proposed that human metaphysical knowledge can only extend as far as human experience. If metaphysics investigates motion in general, it can only understand movers which themselves are the objects of experience. Aristotle's unmoved mover does not qualify, and hence is excluded from Kant's "metaphysics of experience."
Experience, according to Kant, is restricted to things in time, some of which are in space. Psychological states (imagining I am in Hawaii, feeling a pain, falling in love) are in time alone, and physical objects are in space and time. Kant calls these things "appearances," and sometimes speaks of a "sensible world" consisting of appearances. By contrast, my immortal soul (if there be such a thing), God, the unmoved mover, etc. would belong to an intelligible world. Sometimes Kant refers to these as things in themselves. So any metaphysical concepts or principles are restricted to appearances, and the attempt to extend them to things in themselves is the fundamental source of the woes of metaphysics.
To place Kant's system in context, I will contrast three different approaches to the following question: how can we gain knowledge of metaphysical truths? (Recall that for Kant, a metaphysical proposition is one which goes beyond the information provided by experience.) The first appeals to intellectual intuition, the second to inference from experience to something beyond experience, the third to the analysis of concepts.
1. Platonic. On this approach, reason gains insight into special objects (e.g., forms) through a sort of mental vision. The objects of this intuition are beyond experience, as Plato put it, "thought but not seen." Kant claimed that any philosophy based on an appeal to intellectual intuition is mystical. His explanation of the temptation to postulate such a rational faculty is this. Mathematical truths are not known through the senses. They are known a priori, or independently of the information yielded by the senses. It was concluded by Plato and others that the only way mathematics could be known is through a special faculty of intellectual intuition. Once such a faculty is admitted, it is easy to make all kinds of metaphysical claims, e.g. that the good itself is the source of all reality.
What was overlooked, Kant contended (in a footnote to the Appendix to his book Prolegomena to any Future Metaphysics), is that there is a kind of a priori knowledge associated with the senses. In particular, mathematical truths are known because space and time are "forms of sensible intuition." They are absolute prerequisites for the representation of sensible objects; any object of experience must be represented in space and time. Geometry is the science of space and arithmetic of time, and their propositions are necessary truths relative to the objects in space and time. To ascertain this, we reason about the conditions of representation, and intellectual intuition is not needed, and it is not available for other metaphysical claims.
On the other hand, they are not absolutely necessary. To be so, their opposite must imply a contradiction. But Kant recognized the consistency of alternative geometries. So a proposition may be true in one and false in the other (e.g., the sum of the angles of a triangle is 180 degrees, which is true in Euclidean geometry but false in non-Euclidean geometries).
2. Aristotelian. Metaphysical conclusions are established by inference from the information provided by the senses. The argument for the existence of a prime mover is a use of reason to give an absolutely complete account of what we observe through the senses. We see one thing moved by another, and the mover moved by a further mover, and to complete the series, we claim that there is a mover which is unmoved. The unmoved mover is an object altogether beyond the reach of experience. Kant's objections to such an approach were these. First, we have no way of determining whether such claims are true. Second, such claims run into the antinomies, that is, equally persuasive arguments for opposite conclusions. We will look at one example in detail in the next lecture.
3. Wolffian (analytical rationalism). According to Kant's predecessor Christian Wolff, metaphysical conclusions are established through the analysis of concepts. The example we have looked at so far is the ontological argument. The concept of a supremely perfect being is supposed to contain that of existence, so we know that God exists simply by understanding what God is.
Wolff's philosophy was based on the supreme principle of non-contradiction. Any concept which harbors a contradiction does not express a possibility, and hence cannot express a reality. A non-existent God harbors a contradiction, so it is impossible that God not exist. Kant held, on the contrary, that no matter of fact or existence can be established by conceptual analysis. (We will examine the case of the ontological argument in the next lecture.) Synthetic truths, which go beyond mere conceptual analysis, must be established in some other way.
The second principle of Wolff's philosophy was the principle of sufficient reason, that everything that exists does so for a reason sufficient to bring about its existence rather than non-existence. Wolff gave a wretched argument to establish this principle based on the principle of non-contradiction. In other words, he regarded it as analytic. But Kant recognized that it is synthetic. It is always possible that any event that occurs has done so without a cause or any reason at all.
On the other hand, Kant recognized the principle of sufficient reason (for things in time: every alteration of a thing has a cause) as a necessary truth. Kant had claimed that the principles of mathematics are necessary insofar as they are conditions of sensible representation. We can now say that they are synthetic, in that their opposite does not imply a contradiction. Principles of "pure natural science," such as the causal principle just mentioned, are also synthetic and known a priori. They are conditions for the coherence or "unity" of experience. They are needed for us to be able to represent a world of objects as belonging to one single experience.
In general, Kant believed that the task of showing how synthetic judgments can be made a priori is the primary task of metaphysics. He held that the great metaphysicians of the past failed in doing this. Intellectual intuition is a fiction. No inference beyond experience is justified. Analysis of concepts will not yield synthetic truths. We shall examine these alleged failures in more detail next time.
Kant criticized the previous attempts to gain knowledge of the three main objects of metaphysics: the soul, the world and God. Each of these objects goes beyond experience in its own way. God is separate from the created world. The world itself (taken as a totality, a universe or cosmos) is more than could ever come before experience. And the soul is that which is said to be immortal. It is the self, the seat of our thoughts, rather than any thought of which we are aware. The series of the perceptions, ideas or thoughts in our minds itself belongs to experience.
The soul as a thing in itself is said (e.g. by Descartes) to be a simple, unified thinking substance, independent of the body. The simplicity of the soul made it a suitable vehicle for immortality, for what has no parts cannot be destroyed. Hume had claimed, on the contrary, that there is no more to the self or the soul than a series of perceptions. Kant thought there is more to the self than Hume did, but we cannot go into that issue now.
When we experience ourselves, all we find is a series of perception, just as Hume had claimed. However, we claim them all as our own. I am the same thing as I was when I had my prior experiences. Kant recognized that it is true that I am the same thing that has all my experiences, but this is a trivial, analytical truth. Given that they are all my experiences, I am the same thing which has them. But what makes those experiences mine? Like Hume, Kant stated that we can search high and low for the "I" which thinks but can never find it.
Further, although it is analytically true that I am different from any object distinct from myself, this is also an empty claim. Kant held that my body is distinct from myself, but he also said that we cannot know whether I myself depend on my body. Thus he disagreed with Descartes, who held that he is completely separate from his body. Note that these claims are skeptical. Kant did not claim that there can be such a thing as an immortal soul, independent of the body, but only that its existence can be proved from any fact of consciousness. This is typical of his attacks on metaphysics.
It is often claimed in metaphysics that the soul is free. We have seen that this could mean several things, for example, that in my thinking and acting, there is no external impediment. But the deepest sense of freedom is that of thinking and acting in a way that is not determined by any prior state of affairs.
Descartes (Meditation 4) had held that sometimes human beings are undetermined in the sense that they are indifferent between two alternatives. Hume had said, on the contrary, that humans are always motivated to act by a preference for one thing over another. Who is right? Kant thought that the argument could be best understood by considering the world as a whole, to see whether freedom exists there in any form. The issue revolves around the principle of sufficient reason, which states that whatever happens does so in virtue of a reason why it happens rather than not.
On the side of freedom, the argument is that if there were no free acts, there would be no sufficient reason for anything. That is because we could never meet with a happening which does not depend on some other happening. Why did it take place? If a previous happening is given, then the same question could be asked of it, and so on. Reason would never be satisfied; it would never reach a point when it had found a starting point where it would be satisfied.
On the side of determinism, the denial of freedom, the very same principle is invoked in the opposite way. If there were a free act, an uncaused cause (compare Aristotle's prime mover), then it would lack a reason altogether. Nothing would incline events to unfold one way, rather than another. A famous example of this argument is the story of Buridan's ass. This donkey is faced with a choice between eating oats and eating barley, but it has no preference for either one (i.e., it is indifferent between the two). There is no reason, no motive for the choice, so the ass starves to death.
Kant accepted that in the world of experience, we must always seek a determining reason for everything that happens, even though we cannot be satisfied by encountering something absolutely "sufficient." On the other hand, if we think of things as existing beyond experience, there is a possibility of freedom there. We will have to see how there could be such a thing in light of the Buridan's ass problem, but this will have to wait until we study Kant's views on ethics.
The final object of metaphysics is God. Following some of his predecessors, Kant defined God as the most real being. As an object of metaphysics, God transcends the world of experience, and the world of experience cannot provide proof of the existence of such a being. We cannot say that the world is created by God, since we cannot know that it was created at all, rather than existing on its own. And we cannot say that the world was designed by God, since we cannot know the world well enough to tell that it is the work of the most real being.
The only way that the most real being might be proved to exist is through pure concepts. The concept of the most real being includes existence, and so it is analytically true that the most real being exists. But here Kant, like Aquinas, balked. Kant claimed that we can never prove the existence of anything from mere concepts. When I say a thing exists, I am not giving a further description of the thing beyond the concept of the thing itself. If I think of a mountain, then thinking of it as existing puts the concept into relation with a possible experience, e.g. viewing it or climbing it. Put another way, propositions about existence are synthetic and can never be justified by appeal to mere concepts. Saying that something exists does not tell me anything about the concept itself. So trying to prove that God exists from the concept of God is futile. Since experience cannot be used to prove that God exists, there is no way to do so.
For an in-depth look at Kant, see Immanuel Kant's Home Page , designed for Philosophy 175 (Kant).