I am skipping most of the details Kant’s discussion in the last ten pages of the Second Preface on the relationship between his Critique of Pure Reason and the content between his second, slimmer Critique: the Critique of Practical Reason. I do this because I am a bit overwhelmed by the way Kant’s practical-theoretical distinction plays out, and my head spins in comparing his account to Aristotle’s and Descartes’. I am also much more interested in focusing on his theoretical for the time being, seeing how it plays out, and THEN focusing on his practical philosophy. Because the Critique of Pure Reason barely touches on his practical philosophy, I don’t think discussing the bit of preface on his practical philosophy is too important.
So, as a summary, I will just gloss over the entire account of Kant’s philosophical system to wrap up this discussion of prefaces, and in it, I will include the outline of his practical philosophy as well. I may scan a bit of a chapter out of a book that introduces Kant’s philosophy in a few pages, which would explain these things better than I do. But after that, I am going to start on the Introduction to the COPR.
This capacity for sensing (the sensibility), when isolated from actual experience, generates imaginations. For Kant, speculative reason is the result of applying reason to our imaginations. For example (and we will see this discussed in detail later in the COPR), in the same way that we understand that everything must have a cause in the world, we will imagine that there must be a cause outside the real world for the things in the world. We in this way apply what we use on the REAL WORLD to something we imagine outside the real world. Now when we take this speculation to actually be saying something about the real world in the same way as we take our senses to be saying something of the real world, we make a mistake. We think that what we speculate beyond sense experience is the real world (and this discipline of speculating the real world and taking our speculations as true is called metaphysics), but what we speculate to Kant really does not have the same status as what we sense of the real world. To Kant, we must limit the status of this speculation to really what it is: mere speculation.
Those who do not limit speculation in this way, metaphysicians, debate endlessly over the following subjects: does God or does God not exist? Is there free will, or are human beings unfree? Is there an immortal soul or is there not? These are the three issues that become central to Kant’s practical philosophy, which is as follows.
Because Kant says that we must limit speculationand thus remain agnostic about these issues, he claims to paradoxically open up the possibility for resolving these issues once and for all. Here is how: the answer to these metaphysical questions have profound practical implications. If God does not exist, there is no morality; if there is no free will, there is no responsibility; if there is no immortal soul, there is no meaning to life, since it will just as soon be eradicated as it came into being. Kant claims that what metaphysics had been fighting about had been impoverishing a clear and stable practical orientation to the world, since if we do not know the answers to these questions, we cannot know how to live. But, if we need an answer to these questions so much, and which answer we need is pretty clear-cut, then from the perspective of a practical reason, we must say that the answer is what practical life requires. Therefore, God exists, we have free will, and we have immortal souls–because practical reason demands that these be true. What were once disputed within metaphysics are now determined, once and for all, by the demands of what practical reason requires in order to live; where metaphysics had initially said that in the world-in-itself (behind all appearances) existed (or did not exist) God, free will, and/or immortality, now practical reason says that in the world-in-itself (behind all appearances) exists God, free will, and/or immortality. This is the case, even as theoretical reason, which is limited only to what we can know by the senses, says that we CANNOT know these things. We end up with two kinds of world then: a world of appearances, which is known by theoretical reason, and a world-in-itself (a world beyond appearances), which is known only by practical reason.
This way of establishing the truth of something, through an appeal to practical reason, while it seems paradoxical, would come to undergird practically all of modern thought: from Hegel and Marx to Nietzsche and Schopenhauer and Freud to Wittgenstein and Foucault.
Now there is a lot more to Kant, a LOT of really important things, but these don’t seem to be in the prefaces, and we’ll get to them as we get through the book, but this should give a flavor.
*(Metaphysics reached its first pinnacle in Aristotle, from whose book we take the name of the discipline. The origin of the word metaphysics is really this: Aristotle wrote the book, Physics, which was an attempt to account for all change in the natural world, and then he wrote a book after the Physics, which had no title. And so Andronicus, the man to rediscover Aristotle’s books in a library after a Roman invasion of Greece, decided to give a title to this book. Well, one meaning of the particle in Greek “meta” is “after.” So the Metaphysics, “after physics,” is so titled, because it is the book Aristotle that wrote after the Physics. One can of course take the other meaning of the word meta, which is “beyond”, to be the real meaning of meta in the word metaphysics, in which case metaphysics means “beyond physics,” which is roughly the sense in which many have understood the term “metaphysics” to have meant.)