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Immanuel Kant’s Prolegomena is an indispensable guide through the obscure and convoluted tangle of his “critical philosophy,” and it has inestimable value as an introduction to the revolutionary doctrine that he called “transcendental idealism.” In his greatest and most influential book, the Critique of Pure Reason (1781), Kant provides a fresh alternative to what he regarded as the bankrupt approach of traditional, or “dogmatic,” metaphysics, and the dead-end procedures of “skepticism,” as exemplified in the works of David Hume. However, the complexity of this enterprise, combined with Kant’s own professed shortcomings as a writer, made the book almost inaccessible to all but the most diligent reader. The Prolegomena, published two years after the Critique, is Kant’s attempt to clarify and sharpen the main points of the earlier work. It also provides some important elucidations that would appear, sometimes verbatim, in the second, expanded edition of the Critique of Pure Reason, published in 1787.
Immanuel Kant was born in Königsberg, East Prussia (now Kaliningrad, Russia), on April 22, 1724, the fourth of nine children. He entered the University of Königsberg as a theology student in 1740, but through his encounters with the writings of Isaac Newton, his interests soon turned to mathematics and physics. From 1746 to 1755, he worked as a private tutor. For the next fifteen years, he held the position of Privatdocent (lecturer) at the University of Königsberg, during which time he published over a dozen essays on a broad range of topics, including astronomy, physics, metaphysics, natural history, geology, meteorology, medicine, and theology. In 1770, Kant was appointed Professor of Logic and Metaphysics.
The 1770s are sometimes referred to as Kant’s “silent decade.” His energies were focused on his new enterprisea systematic criticism of all dogmatic metaphysics and the development of a new approach, what he called critical philosophy and transcendental idealism. The fruits of this endeavor appeared in the summer of 1781, under the title Critique of Pure Reason (Kritik der reinen Vernunft). This book is the cornerstone of much of Kant’s subsequent thought, and is generally acknowledged to be one of the most important contributions made to modern philosophy. It was followed two years later by the present volume, Prolegomena to Any Future Metaphysics That Can Qualify as a Science (Prolegomena zu einer jeden künftigen Metaphysik, die als Wissenschaft wird auftreten können). In 1785 the Foundations of the Metaphysics of Morals (Grundlegung zur Metaphysik der Sitten) appeared, perhaps Kant’s most accessible book and a seminal contribution to moral philosophy. In 1788 he published his second Critique, the Critique of Practical Reason (Kritik der practischen Vernunft), a “transcendental” exposition of our moral judgments and the regulative ideas of morality. This was followed in 1790 by the third and final Critique, the Critique of Judgment (Kritik der Urtheilskraft), which is his account of teleological and aesthetic judgments. In 1800, Kant’s Introduction to Logic was published. This is a compendium of his lecture notes on various subjects, spanning forty years. Kant died on February 12, 1804, an event described by his first biographer as “a simple cessation of life and not a violent act of nature.”
An understanding of Kant’s Prolegomena requires some familiarity with the issues addressed in the first (1781) edition of the Critique of Pure Reason (referred to as the “A” edition). It is also extremely useful for discerning the motives behind the numerous alterations and additions that were incorporated into the second (1787) edition of Kant’s magnum opus (referred to as the “B” edition). The fundamental concern throughout is to rescue metaphysics, the abused and forsaken “Queen of all the sciences,” and to establish its foundations on firm ground. Kant’s originality and his philosophical genius are most apparent in his ability to bring together disparate and seemingly irreconcilable positions into a new standpoint that acknowledges the basic assumptions of the other positions while avoiding the problems inherent in each. “Critical philosophy” is Kant’s attempt to reconcile the two seemingly incompatible views he referred to as “dogmatism” and “skepticism.”
Dogmatism is Kant’s term for the philosophical approach developed by G. W. von Leibniz (1646–1716) and his student and expositor Christian Wolff (1679–1754). The basic claim here is that necessary metaphysical knowledge is achievable. In other words, we can know, with certainty, various basic truths about the world (e.g., that every thing or event was necessarily caused by some prior thing or event), God (e.g., that God exists, is rational, and good), and human beings (e.g., that we possess immortal souls). Such knowledge depends upon the existence of “innate” ideas or principles that are part and parcel of the rational mind. They are neither derived from, nor directly connected with, sense experience. Once revealed, these ideas or principles can be known with a priori certainty; i.e., they can be known to be necessarily true.
For the dogmatists, all cognition and knowledge involve judgments; and every true judgment expresses a necessary relation between a subject-concept and a predicate-concept. This is Leibniz’s prædicatum inest subjecto principle: the claim that whatever predicate can be truly asserted of a subject depends upon that predicate-concept being contained in the subject-concept. Every true assertion is simply the analysis, the exfoliation, of what is inherent in the subject. Therefore, all true judgments are, on this view, analytic judgments. We know that the assertion “all bodies are extended in space” is true, insofar as we recognize that the idea of spatial extension is implied in the idea of a body. In making this judgment, we are simply unpacking the subject-concept and showing some particular feature inherent in it. And for the Leibniz-Wolffian school, all judgments, even judgments about sense experience, are analytic judgments. The difference between metaphysical judgments and ordinary judgments about sense experience is not a difference of kind, but one of degree. In making a metaphysical judgment, we discern all of the elements of the judgment “clearly and distinctly.” In judgments about sense experience, however, the elements involved are neither clearly nor distinctly known. For example, the judgment that “this chair is mauve” appears to be utterly contingent. It seems entirely possible that the chair could have been ochre or indigo or any other color. Yet, the dogmatists insist that such a judgment is, despite appearances to the contrary, analytic, and therefore, necessary. The necessity is not apparent to finite intellects like ours. An infinite, divine intellect, however, would be capable of deducing the infinite number of steps necessary to analyze the predicate, “mauve,” from the subject, “this chair.” Our inability to do this betrays something about the limitation of human understanding.
Skepticism, on the other hand, is Kant’s term for the basic procedures and claims found in the writings of John Locke (1632–1704) and, more particularly, in the works of David Hume (1711–76). The guiding principles of this approach are the claims that all knowledge is grounded in sense experience, and that no such experience can ever provide us with necessary or certain knowledge. On the negative side, these writers insist that the arguments supplied by the dogmatists to ground their metaphysical claims are simply bad arguments (i.e., invalid and unsound). On the positive side, the skeptical empiricists provide new criteria for what counts as viable philosophical knowledge. Extravagant claims based on mere logical, deductive arguments are no longer allowed. Philosophical feasibility now depends upon sense experience and the procedures of science.
The skeptics contend that, while we do possess the capacity for a priori knowledge, such knowledge is formal and empty, and has nothing to do with the world of sense experience. Logical knowledge involves what Hume calls “relations of ideas,” and deals exclusively with the necessary connections between certain ideas. But the vastly greater extent of our knowledge has to do, not with logic, but with sense experience. Knowledge of the sensible world is what Hume calls “matter of fact” knowledge. It is neither necessary nor certain. It is grounded in sense impressions and their derivative ideas, combined and organized in terms of the mind’s contingent principles of association. The impressions are passively received in sensation. The ideas, which are “mere copies” of the impressions, are then organized by the imagination according to these principles. So to know, for example, that “the cue-ball caused the eight-ball to move,” requires us to acknowledge that causation is involved. In fact, causation is evident in a great deal of our matter-of-fact knowledge. Hume insists, however, that no analysis of any causal situations can ever reveal any sort of “necessary connection” between a cause and its effect. We don’t perceive such a connection; nor is it revealed in any logical consideration of the causal situation. For Hume, our recognition of the causal relation is based upon our customary and habitual experiences of some things being “constantly conjoined” with other things. And our so-called metaphysical knowledge of cause and effect is really just a belief. Belief is an instinctive, psychological feature of the mind that infuses some of our ideas with the “force and vivacity” of an inner impression, such that we are compelled to think or to act in some particular fashion. There is neither certainty nor necessity involved. This is, for Hume, simply a brute fact of the human condition.
Kant’s critical philosophy is an attempt to reconcile Hume’s skeptical conclusions with the claims of the dogmatic Leibniz-Wolffian school. For much of his life, Kant had been a card-carrying dogmatist. For decades he studied and taught metaphysics, using the academic primers written by Christian Wolff and his student Alexander Baumgarten (1714–62). But something profound happened to Kant’s views in or around 1772. He tells us that it was his recollection of “Hume’s problem,” at this time, that “first interrupted [his] dogmatic slumber, and gave [his] investigation in the field of speculative philosophy quite a new direction” (Prolegomena, Introduction). “Hume’s problem” refers to the skeptical conclusions regarding the causal principle: a notion that is fundamental for dogmatic metaphysics. René Descartes (1596–1650) had employed it to prove both the existence of God and the existence of material substances. Leibniz and Wolff saw the causal principle, or its logical manifestation, the principle of sufficient reason, as crucial for our understanding of both God and the realm of phenomenal experience. According to Kant, Hume had shown that, rather than being an offspring of the understanding that provides a priori knowledge of the world, our knowledge of the causal principle is, in fact, “nothing but a bastard of imagination, impregnated by experience, which . . . mistook the subjective necessity of habit for an objective necessity arising from insight” (Prolegomena, Introduction). Thus, the skeptical Hume reduced the causal principle, regarded by the dogmatists as essential for metaphysics, to mere empirical, psychological functions grounded in belief and instinct and incapable of providing us with a priori knowledge.
Critical philosophy emerges, first, in Kant’s attempt to generalize Hume’s problem, i.e., to suggest that Hume’s skeptical observations apply, not just to causation, but to all the other principles of metaphysics as well; and second, in Kant’s desire to trace the origin of these principles to the human understanding, and not to the empirical imagination. Kant’s task, then, is to provide these principles the a priori status that will satisfy our fundamental desire for metaphysical knowledge; a program that he regards as “the most difficult task ever undertaken in the service of metaphysics” (Prolegomena, Introduction). In the first Critique, Kant proceeds in terms of two questions: the quid facti question, which is concerned with describing the facts involved in human knowledge; and the quid juris question, which deals with our right to possess such knowledge. He acknowledges the value of Hume’s description of the facts that are involved in our experiences of causal situations. Yet Hume (and every other philosopher) had failed to even consider the quid juris question. Given the facts surrounding our causal judgments, we must ask, by what right do we make such judgments? What gives us the right, or the justification, for making the judgment “this made that happen?” or for making the general (metaphysical) judgment “whatever happens was necessarily brought about by some prior condition?” Kant’s answers to these quid juris questions express the vital heart of the new philosophical perspective he calls transcendental idealism. In the Prolegomena, as well as in the second edition of the first Critique, the issue is expressed in terms of the question: How are a priori synthetic judgments possible? “Metaphysics stands or falls with the solution of this problem: its very existence depends upon it” (Prolegomena, §5).
How are a priori synthetic judgments possible? The distinction between a priori (necessary and certain) knowledge and a posteriori (experiential, unnecessary, and uncertain) knowledge was a traditional distinction, in common use long before Kant. The distinction between analytic and synthetic judgments, however, is generally regarded as a Kantian innovation. Like the Leibniz-Wolffian philosophers before him, Kant regards all cognitions, all instances of knowledge and conscious experience, as judgments. He contends that the dogmatists were correct in their account of logical, analytic judgments. Such judgments are indeed necessarily true and certain. In the judgment “all bodies are spatially extended,” we can recognize (in a finite number of analytical steps) that the predicate-concept is inherent in, and implied by, the subject-concept. Kant, however, adds to this limited kind of judgment another kind, which is far more common and ultimately, for metaphysics and mathematics, far more important. This he calls synthetic judgment. The constituents of a synthetic judgment are a concept, i.e., a general rule of the understanding that is actively applied to what Kant calls an intuition, i.e., a passively sensed object of experience. So, for example, the judgment, “all bodies have weight,” is a synthetic judgment. While it is true of every body that we encounter in ordinary experience, such truth cannot be found through conceptual analysis. Kant insists that no amount of analysis of the subject-concept “body” will ever unpack or reveal the predicate-concept “weight.” Yet, inasmuch as the statement is true, there must be some kind of connection between the subject and the predicate, one that cannot be found in the judgment itself. According to Kant, we have to go outside the judgment, go beyond the framework of judgments entirely, and call in some tertium quid, some “third thing,” which unites them so that we can know that the judgment is true. The “third thing” that Kant refers to is experience. In order to acknowledge the truth of the judgment “all bodies have weight,” we must generalize on the basis of our experiences of this particular body having weight, another particular body having weight, and so on. And it is to these experiences (or the memories of them) that we appeal in order to recognize the truth of this judgment. Since the truth is revealed not through analysis of concepts, but through an appeal to actual sense experience, judgments of this sort are synthetic judgments.
But what is the status of the objective realm of experience, which makes our synthetic judgments true? Kant contends that either there is such a realm, which we can know in terms of metaphysical, scientific, and commonsense judgments, or there isn’t. To say that there isn’t commits one to dogmatic idealism: the view that only minds and their ideas (perceptions, conceptions, etc.) exist. Such a view is incapable of showing how real, objective knowledge is possible, since there is no objective realm to know. If, on the other hand, we deny dogmatic idealism and acknowledge the existence of a real world of spatio-temporal things, then commonsense experience and scientific knowledge seem to be possible. However, to acknowledge a world of objects that are completely independent of the human mind, objects that are “things-in-themselves,” commits one to transcendental realism: the view that objectivity is beyond the pale of human experience and knowledge. If the objects are, like Leibnizian substances, utterly independent of one another and of the knowing mind, then we have no cognitive access to them, and objective knowledge in metaphysics and in the sciences becomes impossible. So neither dogmatic idealism nor transcendental realism is able to accommodate the basic conditions of objective knowledge.
The so-called “Copernican revolution” in Kant’s philosophy involves our going against the traditional assumptions and our commonsense beliefs about the world. Instead of regarding the objects of experience as mere conceptual parts of the mind (which fails to account for their objectivity), or as things that are radically independent of the mind (which fails to account for our knowledge of objects), Kant suggests that we take a new tack. What if the objects of human experience and knowledge, as well as the conditions of objectivity, have their origin in the knowing subject? Contrary to dogmatic metaphysics, Kant contends that there is a real, objective, independent realm of spatio-temporal objects that are presented to us in sensation. Contrary to skeptical empiricism, he argues that we are capable of real, objective, a priori knowledge of this realm. Kant’s transcendental idealism holds that we can make necessarily true judgments about sense objects just because the human mind itself produces these objects and the necessary conditions of their existence. This revolutionary approach to understanding objectivity and metaphysical knowledge may, like Copernicus’ description of a heliocentric system, seem strange and counter-intuitive at first. But once we see how, on this view, we are able to satisfy our fundamental desire for metaphysical knowledge, our philosophical prejudices and preconceptions will fall away.
For Kant, the human mind is made up of two radically different “faculties,” or powers. On the one hand, there is the faculty of sensibility, which passively receives the sense-contents of human experience and empirical knowledge. Sensibility is the part of the mind that contains intuitions, or the sensible, particular elements of empirical knowledge. On the other hand, Kant insists that we also possess the faculty of understanding, the mind’s spontaneous and active powers. While sensibility provides the passive, particular contents of our knowledge, the understanding is the source of the active, general rules of human cognition, or concepts. All real, objective knowledge involves the subsumption of some passive intuition under an actively employed concept. The result is a synthetic judgment, an expression of the unity between the two radically different parts of the mind: sensibility and understanding. This is Kant’s characterization of the facts involved in our ordinary, empirical knowledge; an account that is not too different from Hume’s. The difference in the two accounts, however, makes all the difference regarding the possibility of metaphysics. In examining an ordinary empirical judgment, such as “this is a chair,” the sensible part of the mind receives the “this,” while the active part of the mind, the understanding, finds and applies the concept “chair,” so that we can make the judgment. There is obviously nothing necessary or certain here. The intuition may or may not be received, the proper concept may or may not be found and applied, the judgment may or may not be made, or, if it is, it may or may not be true. So, as Hume so thoroughly pointed out, all such knowledge is a posteriori in nature, devoid of any necessity or certainty. Kant agrees that, so far as the facts of experience go, such empirical judgments are mere a posteriori, synthetic judgments. The same is true of a judgment like “the cue-ball caused the eight-ball to move.” There is nothing in the judgment, so far as the facts are involved, that betrays any necessity. However, when Kant asks the question, by what right do we judge this to be a cause and that to be an effect?, the situation changes dramatically.
Here Kant is asking, what has to be the case in order for us to make causal judgments? He contends that, prior to our experience of the particular, empirical intuitions, our passive faculty of sensibility must initially provide us with pure intuitions; i.e., representations that are not derived from sense experience, but which are the a priori conditions of such experience. These are space and time. All of our cognitions must occur in space and/or in time. That these conditions originate in the knowing subject is demonstrated by the fact that our mathematical knowledge is both necessary (a priori) and synthetic; i.e., the truths can be “shown,” or “exhibited,” in sense experience. For example, we can know with certainty that 7 plus 5 equals 12, by drawing 7 marks and 5 marks on paper, and counting the 12 marks. The necessity of all such arithmetical (and geometrical) truths can be exhibited in sense experience, making these judgments both a priori and synthetic. Another necessary condition for our knowledge of the sensible world involves the acknowledgement of certain pure concepts of the understanding. Just as an ordinary empirical judgment asserts a connection between an intuitive element (the sensible intuition) and a conceptual element (the empirical concept), the necessary conditions for human experience and objective knowledge consist in our pure intuitions of space and time being subsumed under the pure concepts. These concepts are pure insofar as they are inherent in the understanding, and were not derived from sense experience. There are twelve such concepts, and, together, they comprise the concept of an object in general, i.e., all the necessary conceptual elements of what we call objectivity.
When these a priori concepts are united with the a priori intuitions of space and time, through the activities of what Kant calls the transcendental synthesis of imagination, we have a spatio-temporal manifold which contains in it objects that have been produced and organized according to certain necessary principles. These principles assert something about how the pure intuitions have been organized by the pure concepts, such that human experience becomes possible and metaphysical knowledge becomes viable. So, for example, the causal principle, which asserts that everything that occurs was necessarily brought about by some prior cause, can now be regarded as a true metaphysical principle, an a priori synthetic judgment. Even though, as Hume had indicated, I can never be certain what caused what, I can nevertheless be certain that if something happens in my sense-experience, then something which preceded it in time caused it. This principle reflects how the pure concept of causation organizes the spatio-temporal manifold. And we would not be able to make such a priori assertions about objects unless we have provided the necessary conditions for their existence and organization.
Like the dogmatists, Kant claims that our metaphysical assertions about the world are necessary and universally true, i.e., they express a priori certainty. Like Hume, Kant claims that no such necessity, universality, or certainty can be revealed through an empirical examination of the facts involved in such assertions. The assertion “this cue-ball caused that eight-ball to move” can be regarded as true only tentatively and contingently. For one can easily imagine situations where such a claim is false; for example, if the eight-ball has been glued to the table and doesn’t move or if the eight-ball is made of painted glass and shatters. Kant’s transcendental idealism starts with an ordinary, perceptual situation, and then asks, what has to be the case in order for us to have such experiences? Or to put the situation in its more general framework, what has to be the case in order for us to regard every sensible thing or event as caused by something? Inasmuch as this judgment is in the realm of sense-experience, it is a synthetic judgment. And insofar as we are asking, “what has to be the case,” the judgment will be a priori. The “third thing” that connects the subject and predicate in such a judgment cannot be some particular sense experience. It is, according to Kant, the mere possibility of any experience whatsoever. Thus the limitations of both dogmatism and skepticism are overcome.
When Kant’s first Critique appeared in the summer of 1781, it was met with silence. The revolution in philosophy that Kant expected didn’t happen. It wasn’t until the following winter, in January of 1782, that a review finally appeared in the periodical Zugaben zu den Göttinger Gelehrte Anzeigen. It was written by Christian Garve (1742–98), a classics scholar and philosopher, and it was edited “with the breath of pure animosity” by J. G. H. Feder (1740–1820), a man who would show himself to be a very vocal critic of Kant’s critical philosophy. Garve’s untainted (and more charitable) review appeared in August 1782, in the journal Allgemeine deutsche Bibliothek. Both versions were, for the most part, successful in clarifying the exceedingly dense and convoluted arguments in Kant’s book. Yet Kant was gravely offended, particularly by the earlier, “mutilated” version. He was outraged by Feder’s contention that transcendental idealism amounts to nothing more than a restatement of George Berkeley’s (1685–1753) radical idealism. Berkeley’s principle, esse est percipito be is to be perceivedwas taken by many, including Kant, to imply the abandonment of an objective reality, and an endorsement of the claim that only perceiving minds and their perceived ideas exist. For Kant, this view represents the demise of all a priori knowledge in both metaphysics and in mathematics.
The Prolegomena was written during the fall of 1782 and published just before Easter 1783. It is Kant’s attempt to make clearer the main points of the first Critique, and to emphasize the real and objective nature of our experience and knowledge. Kant says that the first Critique was presented in a “synthetical style,” while the Prolegomena is executed according to “an analytical method.” In other words, the first Critique begins with certain facts of ordinary experience and provides a transcendental account of the necessary conditions for the possibility of such facts. These conditions are expressed in terms of various metaphysical principles that express the a priori laws of objective, human cognition. The Prolegomena, on the other hand, assumes that we have a priori knowledge of the appearances (i.e., necessary mathematical and metaphysical cognitions), and it proceeds to establish the fundamental features of such knowledge, while avoiding the subtle, hair-splitting style that characterizes the earlier book.
In the first Critique, Kant draws a sharp distinction between transcendental realism, which holds that space and time (and the objects contained therein) are real, objective things that exist independently of the human mind (as “things-in-themselves”), and his own transcendental idealism, which holds that space and time are the a priori forms of sensibility, and that the objects of human cognition are “appearances” that originate in the knowing mind. He insists that “[t]he transcendental idealist is . . . an empirical realist, and allows to matter, as appearance, a reality which does not permit of being inferred, but is immediately perceived.” He is here identifying transcendental idealism with empirical realism, the view that the spatio-temporal appearances are objectively real, and are directly perceived by us. Kant’s critics (e.g., Feder), however, assumed that a dismissal of transcendental realism leads one to embrace dogmatic idealism, i.e., the view attributed to Berkeley, which holds that only minds and their ideas exist, and no knowledge outside the circle of our ideas is possible.
Much of the Prolegomena, as well as many of the additions that would be incorporated in the second edition of the Critique of Pure Reason, are intended to make clear the limitations of both transcendental realism and dogmatic idealism and to illustrate the truth of Kant’s transcendental idealism. To this end the second edition (1787) of the first Critique excludes the discussions that focus on the subjective side of knowledge (e.g., the so-called subjective Transcendental Deduction, the original Paralogisms chapter), and emphasizes the objective aspects of human knowledge (e.g., the revised discussions in the Transcendental Deduction, the Axioms chapter, and, most explicitly, Kant’s “Refutation of Idealism”). The Prolegomena also makes clear an implied tripartite division of the first Critique in terms of the discussions of mathematical knowledge (§§1–13; cf. the Transcendental Aesthetic), of metaphysical knowledge (§§ 14–39; cf. the Transcendental Analytic), and of the misapplication of human reason to claims about God (§§40-60; cf. the Transcendental Dialectic). The first two discussions show the features and functions of the mind that are involved in a priori synthetic judgments (mathematical and metaphysical judgments, respectively), while the third discussion indicates the limits of human knowledge that are surreptitiously transcended in the dogmatic attempts to achieve knowledge of God; knowledge of a domain outside the appearances and beyond the pale of human knowledge. Finally, in the appendix to the Prolegomena, Kant strikes out against Feder’s misunderstanding and misrepresentation of the issues in the first Critique. Foremost among these is the (false) claim that the abandonment of transcendental realism leads to the adoption of dogmatic idealism. Kant attributes this confusion to Feder’s impatience with complex arguments; or to his vexation with a view that doesn’t jibe with his own metaphysical preconceptions; or to simple narrow-mindedness. In any case, Kant insists that Feder’s review reflects the common practice among philosophers of taking some original insight or innovation, of bleeding from it all originality, and of forcing it into the procrustean bed of prior preconceptions. Such an approach does justice neither to the innovation nor to the critic.
Kant’s transcendental idealism was both the culmination of the efforts of many writers in early modern philosophy, and also the springboard for much that would follow in nineteenth-century philosophy. The two editions of the Critique of Pure Reason and the Prolegomena are the pivots of Kant’s revolutions in metaphysics and epistemology. The latter work brings to light and corrects many of the stylistic and conceptual problems of the first edition of the Critique; and it prepares the way for many of the new or amended discussions contained in the second edition.