Summary
Kant begins the Prolegomena by stating his intention to distinguish philosophy—as he calls it, metaphysics—from mathematics and the natural sciences, particularly physics. He proposes to do this by defining its field of inquiry. Metaphysical judgments cannot be based on experience because, by definition, metaphysics is the use of the human mind to obtain a priori knowledge—literally, knowledge that precedes experience. Metaphysical knowledge comes not from observing the world, but from pure reflection. Physics and psychology are based on experience of the outer and inner world, respectively, so metaphysics’ closest analog is mathematics. He will begin by distinguishing the two.
Before beginning, however, Kant draws a distinction between two kinds of a priori judgments: analytical and synthetic. Analytical judgments add nothing to the object that they describe. They are sentences in which the subject and the predicate are identical—for example, sentences like "all bodies (physical objects) are extended in space," "all bachelors are unmarried," "gold is a yellow metal." To be a body means, by definition, to take up space, therefore that is an analytical judgment. All bodies have weight, however, is a synthetic judgment, because to have weight does not belong to the definition of being a body.
The validity of an analytic judgment is easy enough to test. So long as the predicate is identical with the subject, and does not contradict it, an analytic judgment is valid. How can we test the validity of synthetic judgments? First, by experience. All judgments from experience, or a posteriori judgments, are synthetic, because our senses are constantly furnishing us with new information about the things we perceive. By actually meeting several bachelors, for example, we might learn that some are named Richard. Kant calls these statements synthetic a posteriori judgments.
What about synthetic a priori judgments? Are such judgments even possible? Kant contends that they are. Here, mathematics furnishes with the readiest examples. The statement “7+5=12” is certainly a priori, since we know in advance it is true for all objects—we dont need to add up every object in the world in combinations of seven and five to find out if they will equal twelve. And while at first this equation would seem to be analytical, since the subject and the predicate are the same, on closer inspection, it proves to be synthetic, because the concept “12” is contained neither in the concept “5” nor in the concept “7.” It is more than the sum of its parts. Furthermore, from the concept “12” we can glean still more information not contained in the original statement—“9+3”, for example, or “10+2.”
Kant believes that philosophers before him, especially Hume, have overlooked this aspect of mathematics. In Hume’s view, the concept “12” only means “the number you get when you combine seven and five.” This mistake has, in turn, led philosophers to misunderstand the task and the method of philosophy, which is to obtain synthetic a priori knowledge.
Unlike mathematics and physics, however, which have a close relationship to the observable world, the concepts about which metaphysics attempts to gain a priori knowledge—God, for example, the immortal soul, human freedom, whether the world is finite or finite—cannot be proven or disproven by experience. The entire metaphysical enterprise, then, rests on the possibility of synthetic a priori knowledge.
Fortunately, mathematics and the natural science show us that synthetic a priori knowledge is possible. The aim of the Prolegomena will be to determine how these sciences function, to determine what metaphysics has in common with them, and finally, to determine how it is distinct.
Analysis
Before jumping into the technical questions at the start of the Preamble to Kant’s Prolegomena, it is worth taking a glance at the rhetorical remarks at the end. These offer us important insight into Kant’s understanding of what it means to “do” philosophy, where philosophy is in its history, and how Kant sees himself as contributing to its development, all of which will help us better understand the more technical aspects of his argument.
First and foremost, Kant insists that philosophy, or metaphysics, is a science. Consequently, Kant’s points of reference for philosophy are not other spiritual forms, like art and religion, as they are for later philosophers like Hegel and Nietzsche, but mathematics and the natural sciences. Like philosophy, physics and mathematics are entirely abstract, and yet no one doubts their findings—we don’t need to ascertain that, for every single object on earth, two and two will make four. Unlike math and science, however, philosophy has habitually overstepped its bounds by claiming to have knowledge of things it couldn’t possibly know. By putting philosophy on a proper scientific footing, Kant hopes to do for philosophy what Isaac Newton did for mathematics and physics—to make it into a science that can produce judgments as self-evidently and inarguably true as 2+2=4.
First, says, Kant, we must determine what kind of knowledge philosophy should be trying to obtain. That returns us to the technical aspect of Kant’s argument. Kant begins by sketching out the different kinds of judgments, or statements of knowledge, a science can make. Kant wants to know which of these metaphysics should be after, and how we can be certain that these judgments are true. By answering these questions, metaphysics will be able to establish itself as a true science. Hence the full title of the book: Prolegomena to any Future Metaphysics Grounded As a Science. In ancient Greek, “prolegomena” means prologue, or introduction. Kant sees his work as preparing the way for philosophy’s proper beginning.
Kant’s first distinction is between judgments a priori and a posteriori—from the intellect and from experience. For metaphysics to function as a science, it must be able to make a priori judgments, judgments that precede experience and that are true for all experience, just as physics can establish that every action must have an equal and opposite reaction, without having to confirm this hypothesis with every possible object in every possible situation.
Kant divides a priori judgments once more into analytic and synthetic judgments. Analytic judgments are judgments in which the subject and the predicate are the same: all bachelors are unmarried, for example. Synthetic judgments, on the other hand, tell us something new about the object under consideration: some bachelors are blond. We can only learn this by meeting several blond bachelors; therefore, it is a synthetic a posteriori judgment. A properly scientific metaphysics would be able to provide us with synthetic knowledge a priori, that is, would provide us with new information about the world through the intellect alone.
Kant was the first philosopher to distinguish between analytic and synthetic judgments. Before him, philosophers tended to think that all abstract thought was fundamentally analytic, especially mathematics. For David Hume, “7+5=12” is an analytic statement; “twelve” is not a concept, so much as it is another way of saying “the number you get when you add seven and five.” Math, therefore, is a circle of definitions. Kant, who had studied mathematics extensively, disagreed with Hume; most mathematicians today would agree.
Still, the distinction between analytic and synthetic judgments poses some problems. How can we tell what belongs to a concept necessarily? It seems certain that all bachelors have hair, and yet, having hair does not belong to our concept of being a bachelor. Kant would reply that we could imagine a perfectly hairless bachelor, even if one doesn’t exist. But here the experience of meeting bachelors with hair day in, day out, would provide a considerable temptation to count this judgment as analytically true.
The reader will notice the importantance of the term “judgment” to Kant, and though he did not originate it, it is widely associated with his philosophy. Throughout the Prolegomena, and particularly in the rhetorical remarks at the end of the Preamble, Kant uses many legal metaphors, and characterizes our minds as a kind of judge. In the Critique of Pure Reason, he refers to Reason as a “tribunal.” In the “Groundwork for the Metaphysics of Morals,” he says that only those moral actions are truly free that can form the basis for a universal law. Thinking, for Kant, is not a creator so much as it is a regulator. It obeys rules and laws, and enforces them on our sensory perception. We will examine this process in greater detail in the second and third sections of the Prolegomena.
