In the previous essay in this series, we saw Heidegger claiming that Leibniz “prepares” the completion of the metaphysical tradition, but that it is Nietzsche who actually brings it about. I will devote a future essay to Heidegger’s interpretation of Nietzsche, but we may note here that the completion of metaphysics would have been impossible without Kant, who answers Leibniz and inadvertently prepares the way for Nietzsche. In this essay, I will introduce readers to Kant’s extraordinarily important and difficult philosophy. In my next essay, I will discuss Heidegger’s critique of Kant. Readers who feel they are already familiar with Kant should take note that the present essay may contain some surprises. Plus, I will be focusing on matters that are of central importance to Heidegger’s critique.
Immanuel Kant was born in Königsberg in 1724 and died there in 1804, having spent his entire life in the vicinity. The details of Kant’s life need not detain us. As Heidegger once said of Aristotle, “He was born, he thought, he died.” All that matters are his ideas. And it would be difficult to overstate the importance of Kant’s ideas in the history of philosophy, and their influence on every area of thought in the West. Kant is accurately described as an “epochal” philosopher, meaning that he inaugurated a new epoch in the history of Western thought. Indeed, his ideas mark such a major turning point that it is quite legitimate to speak of philosophy before and after Kant. After him, it would, for better or for worse, never be the same. (Among other things, after Kant the writings of philosophers would never again be intelligible to the general public.)
Kant is both an extraordinarily profound thinker, and an extraordinarily problematic one — in three major ways. First, he consciously and deliberately poses serious problems for the ambitions of metaphysicians (both those who came before him and those who came after). Second, his writings pose major problems of interpretation (scholars have never stopped fighting over what Kant really meant). Third, Kant is a problematic figure because, ultimately, he is a transitional figure whose thought is inconsistent: he poses serious challenges to some of the deepest assumptions of modern philosophy, while seeming to buy into some of those assumptions at the same time. This is one of the major reasons why his writings pose so many interpretive challenges — and it is also at the heart of Heidegger’s critique of Kant.
2. Kant’s Discovery of Transcendental Subjectivity
Let’s begin by considering to whom Kant was responding in his work. Conveniently, his targets fall into two groups, the rationalists and the empiricists. While the empiricists actually called themselves “empiricists,” the term “rationalism” was not used at the time. The so-called rationalists had no term for themselves but were called by their opponents “dogmatists” and “school philosophers” (this latter term registers a perceived continuity between modern rationalism and medieval scholasticism). The major rationalists were Descartes (to whom I have devoted an entire essay  in this series), Spinoza, Leibniz (to whom I devoted another essay ), and Christian Wolff. Wolff is not generally regarded these days as an important philosopher in his own right but is seen instead merely as the man who systematized Leibniz’s ideas. (In other words, he is the man who made Leibniz’s system even more systematic; on the idea of a philosophical system see my Leibniz essay.)
The term “rationalism” is used today in broad and narrow senses. Broadly, it is used by laymen to mean commitment to the idea that issues, of whatever kind, should be settled by the use of reason. Thus, even natural scientists are sometimes referred to these days as “rationalists,” though in fact they are generally committed to some form of empiricism, weak or strong. Historians of ideas use “rationalism” exclusively to refer to the early modern philosophical movement that held that truths about the universe may be discovered through the use of pure reason, unaided by the senses. This is the common assumption underlying the very different philosophies of Descartes, Spinoza, and Leibniz-Wolff.
Significantly, Kant began his intellectual life as a follower of the Leibniz-Wolff school; in other words, he began as a committed rationalist. Yet rationalism is the “pure reason” taken to task in Kant’s seminal work The Critique of Pure Reason (1781; referred to by scholars as the “first Critique” so as to distinguish it from The Critique of Practical Reason, 1788, and The Critique of Judgment, 1790, neither of which will be discussed here). Somewhere along the way, therefore, Kant became disenchanted with the Leibniz-Wolf philosophy.
Partly, this was due to the influence of empiricism, which was a philosophical movement defined in conscious opposition to the rationalists. Empiricism rejected the use of pure reason and affirmed instead the diametrical opposite position: the senses and the senses alone provide knowledge of the world. The empiricists who have stood the test of time (i.e., whose works are still read today) are Locke, Berkeley, and Hume, though it was chiefly Hume’s work with which Kant was acquainted.
In both his Treatise of Human Nature (1739-1740) and Enquiry Concerning Human Understanding (1748), Hume famously raised a skeptical problem about the idea of causality, though Kant appears only to have read the latter text. Hume observed that we believe in something called “necessary connection” in cause and effect relations. To take a very Humean example, if we hit a billiard ball with a cue stick it rolls away, so long as it is unimpeded. We believe that if the same causal event (the cue stick striking) occurs again in the same way, the exact same effect (the ball rolling) will follow. Indeed, we think it has to follow, because we believe that such causal relations are “lawlike” and “regular.”
Hume pointed out, however, that if we adhere to strict empiricism we must acknowledge that we never see (or otherwise sense) this thing called “necessary connection”; it is just an idea. Moreover, our assumption that the same circumstances will produce the same effects in the future is based upon the deeper assumption that the future must resemble the past. We think we are justified in this assumption because when, in the past, we’ve anticipated that certain events would play out tomorrow just as they did yesterday, we were proved right — repeatedly. But Hume correctly observed that we never really know that the future will resemble the past because no one has actually been to the future. Perhaps next time (in the next future) things will happen differently; perhaps tomorrow that billiard ball will behave very unpredictably. We cannot rule this out. Thus, our confident assertion that certain things “must” happen the same way in the future is, for Hume, not even worthy of serious consideration.
Now, it is important to say immediately that Hume did not convert Kant to empiricism. Indeed, the empiricists become one of Kant’s targets as well. But Kant credited Hume’s problem of causality with awakening him from what he called his “dogmatic slumber,” i.e., his commitment to the Leibniz-Wolff philosophy. Kant took Hume’s conundrum very seriously, and what particularly interested him was the way the human mind seems to automatically infer necessary connection when it has no real empirical basis for doing so. Hume’s explanation for this was that we simply form a “habit” of expecting things to keep happening the same way, based upon repeated experiences.
Kant found this explanation inadequate because, among other things, I regularly infer necessary connection even from a single cause-effect instance. For example, when the personnel of the Manhattan Project exploded the first atomic bomb, no one said “let’s do it another dozen times or so to see if the same conditions produce the same effect.” A single instance was sufficient to convince them that they had discovered a new cause-effect relationship that was necessary, lawlike, and would happen the same way again in the future. It seemed to Kant as if our minds were “pre-programmed,” as we like to say today, to see the world in terms of necessary connections in cause and effect. In other words, Kant claims that our experience of the world is only possible through, among other things, a prior assumption about cause and effect — an assumption not derived from experience, as Hume held, but one that underlies it and makes our sort of experience of the world possible in the first place.
In short, Kant’s confrontation with Hume led him to discover the realm of the a priori or the transcendental (terms which will be explained anon). Suppose that the mind contains all sorts of innate assumptions that it brings to all experiences. These assumptions “structure” our experience — specifically, they structure the “input” from the sense organs — in order to make experience possible at all. Now, rationalists like Descartes and Leibniz were famous for having affirmed the existence of ideas in the mind that were called “innate,” i.e., not derived from experience. However, Kant was saying something quite different from this. The innate ideas of the rationalists were, more or less, innate pieces of information. For example, Descartes and other rationalists believed we have innate knowledge that God exists. They also believed (with Plato) that knowledge of mathematics is innate.
However, Kant affirmed the existence not of innate information but rather of innate mental rules (Regeln, a term he often uses) which work behind the scenes to make our experience of the world possible. Kant states that the understanding “has rules which I must presuppose as being in me prior to objects being given to me, and therefore as being a priori” (B xvii; italics added  ). To speak rather loosely, innate ideas are static; they say “x is y” or “there is x.” Kant’s structural rules are dynamic, they are active in forming experience; they say “whenever x, derive y” or “whenever x, produce y.”   Kant designates these innate subjective functions with the Latin adjective a priori, which simply means that they are a type of “knowledge” held prior to, or independent of any sense experience. That we interpret the world in terms of necessary connection in cause and effect is one such a priori rule. By contrast, my knowledge that smoking causes cancer is a posteriori; it is derived from experience (it is consequent upon, or posterior to, or simply after experience).
Instead of “a priori” Kant also often uses the troublesome word “transcendental.” In the first Critique, Kant writes “I entitle transcendental all knowledge which is occupied not so much with objects as with the mode of our knowledge of objects in so far as this mode of knowledge is to be possible a priori” (A 11, B 25). In other words, “transcendental” refers to the subjective conditions that make knowledge possible. Our aforementioned conviction regarding causality is one such transcendental condition of knowledge. By contrast, my knowledge that smoking causes cancer is empirical; it is achieved knowledge of the world, derived from experience, not a condition making such knowledge possible.
The Critique of Pure Reason is devoted, in large part, to detailing various a priori or transcendental structures that Kant believes are constitutive of experience (i.e., presupposed by all possible experience). There are far too many to discuss here, and much of Kant’s treatment of these structures is complex and obscure. We have already mentioned one, the “category” of cause and effect. We might also mention two others, just to give the reader a couple more examples, and a taste of the sort of “transcendental arguments” Kant presents.
Kant identifies both space and time as a priori “forms of intuition” (where “intuition,” Anschauung, simply means “sense perception”). We perceive all external objects, such as the laptop in front of me, as “in space.” Yet what is space? To speak loosely, it seems to be a kind “container” in which objects are given (e.g., the laptop and coffee cup in front of me occupy space and exist in spatial relations relative to each other). Yet space itself is not an object that is perceived. All objects of sense perception are given in space, but space itself is not a “thing” given in space and is not sensed with any of the five senses. So then what is it? Kant answers that space is transcendentally ideal: space is a feature of the way our subjectivity constitutes objects in the world, but it is not itself an object in the world. If subjectivity did not exist, space would not exist.
Kant takes a similar position with respect to time. He observes that all objects of experience whatever are given in time, both external objects such as the laptop and the cup (which persist through time or occupy different places at different times) and “internal objects” such as thoughts and feelings, which are also experienced as “taking time.” (By contrast, only external objects are experienced as in space.) But what is time? Like space, it seems to be a sort of “container” in which things exist or persist, but is it a thing itself? I cannot perceive time with any of my five senses. Further, in order for the passage of time to exist my mind has to retain prior events in memory. For example, it is only by remembering the start of the journey, and the events that intervened between start and finish, that we are able to say the journey “took a long time” or “a short time,” or any time at all. The mind also protends futurity (to use Husserlian language): part of the experience of time is the expectation of future events that are not yet real. But that means that this expectation is not based on anything empirical. If time depends upon mental retention and protention, it is hard to escape the conclusion that time is a feature of subjectivity, and not a feature of the world.
These conclusions are usually fiercely resisted by anyone hearing them for the first time. Is Kant saying that space and time are not real? Yes and no. They are certainly a constant feature of my experience, and, indeed, of everybody’s experience. Thus, it would be wrong to characterize them as “illusory.” Yet, Kant affirms that they have no reality independent of our experience of them. At the same time, as we shall see, he affirms the independent reality of objects given in space and time. This usually produces much confusion: how can the laptop “be” at all if it is not really in space and time? This sort of consternation is inescapable and, in a way, proves Kant’s point about the constitutive role of transcendental structures. It is indeed absolutely impossible to conceive of the laptop apart from how it appears to us in space and time, even though we know (if Kant is correct) that space and time are not “real.” This simply illustrates how powerful the transcendental conditions of human experience are: they shape our knowledge and experience to such a degree that we cannot even imagine an experience (or a world) that is not governed by them.
Kant’s discovery of transcendental subjectivity was an epochal achievement in philosophy for the simple reason that no one had ever thought of this before. Though earlier philosophers had spilled much ink concerning the nature of knowledge and truth, none of them had entertained the possibility that our experience might be the result of innate structures of subjectivity which give form to the raw matter provided by sensory input (what are often called “sense data” in later philosophy). Another, more striking way to put this is to say that, for Kant, the objects we experience are constructed by subjectivity. When I have the experience of seeing this laptop, it is the end result of transcendental structural processes of which I am not consciously aware.
3. Kant’s Copernican Revolution and the Critique of Metaphysics
Kant’s discovery launched a revolution in human self-understanding, and Kant himself understood that it would. In the first Critique, he likens it to Copernicus’ demolition of the geocentric model. Copernicus conclusively demonstrated that the sun stands still and that we move around it, even though sense perception seems to suggest the exact opposite of this (i.e., it appears to our eyes as if the sun is “rising” and “setting”). Understanding Kant’s discovery of the a priori requires that we perform a similar “gestalt switch” in understanding how our minds relate to objects in the world. He writes in the preface to the second edition of the Critique:
Hitherto it has been assumed that all our knowledge must conform to objects. But all attempts to extend our knowledge of objects by establishing something in regard to them a priori, by means of concepts, have, on this assumption, ended in failure. We must therefore make trial whether we may not have more success in the tasks of metaphysics, if we suppose that objects must conform to our knowledge. [B xvi]
This is Kant’s “Copernican Revolution” in philosophy.
Now, what has been said so far might lead one to conclude that Kant is a kind of modified Leibnizian. Recall that in my last essay I discussed how Leibniz believed that all objects are phenomenal; i.e., they have no reality outside of minds (there is no “external world” of material objects for Leibniz). However, Kant rejects this position. He affirms that the objects we experience do have correlates in the world outside our minds. There are, in other words, “things out there.” These things act upon what Kant calls “sensibility” (Sinnlichkeit; i.e., our sense organs) and then the transcendental structures of subjectivity give form to these sense data. The result is that the “object” I experience, while it has a basis in sense input, is also a result of the unconscious constitutive or constructive properties of subjectivity.
So, Kant believes that we really do know objects “out there in the world.” However, he insists that we only know those objects as they appear to us, never as they are “in themselves.” This claim is central to Kant’s philosophy, and it has been the subject of enormous controversy. If Kant is right that the object, as I experience it, is partly a construction of a priori functions in my mind, then it must follow that I only know the object as it appears to me. Suppose we ask, “Yes, but can we know what the object is really like, independently of how it appears to us?” Kant answers that we cannot — and that it ought to be obvious that we cannot. To know objects independent of how they appear to us would require knowing them independently of any determinate structures or process of knowing. This means that our question really amounts to asking, “Can we know what the object is really like, independent of knowing it?”
But this, of course, is absurd. It is like asking “Can I digest my food without its going through my digestive tract?” (i.e., “can I digest my food without digestion?”). All knowing involves a process by which objects are given to a subject. To know “independently” of any process would have to be some kind of miraculous “direct knowing.” The point that Kant is making here is now very familiar to us moderns (thanks in part also to the discoveries of cognitive science) and so we might think that he is just stating the obvious. It is therefore very important to keep in mind that previous philosophers really did maintain, either consciously or by implication, that “direct,” unmediated knowledge of reality was possible; i.e., knowledge without process, or the contribution of subjective structures. Both Plato and Aristotle seem to explicitly hold that such knowledge is possible. Other philosophers also presuppose, unreflectively, that direct knowing takes place. For example, every representationalist claims that direct knowing of external objects is impossible — but then posits that we can directly know internal “representations,” without ever realizing that if one form of direct knowing is problematic then so is the other.
To refer to objects as they appear to us, Kant borrows the term “phenomena” from Leibniz (the term simply means “appearances”). He contrasts phenomena to “things as they are in themselves,” or, more briefly, “things in themselves,” or “the thing in itself’ (Ding an sich). To offer one simple illustration, I only know the coffee cup as it appears to me, as a phenomenon. The coffee cup “as it is in itself” — i.e., the coffee cup as it is independently of its appearing to me — I can never know. Sometimes this distinction is given as “phenomena” vs. “noumena.” However, Kant’s use of “noumena” is complex. It can, in some contexts, refer to things in themselves, but in other contexts it refers to “thought objects” which men believe they know, but which never appear to the senses, such as God or the soul. It is best to set this complicated term aside and to frame the above-discussed distinction as between “phenomena” and “things in themselves.”
Now, this distinction gives rise to a whole host of questions and problems. First of all, how do I even know that things in themselves actually exist? Perhaps only appearances exist “in my mind.” (This way of framing the question presupposes the representationalist model of knowledge, which we will explore in the next essay with respect to the question of whether, or to what extent, Kant is beholden to it.) Kant’s answer to this problem is little more than an appeal to commonsense. He says that although we cannot know objects as things in themselves “we must yet be in a position at least to think them as things in themselves otherwise we should be landed in the absurd conclusion that there can be appearance without anything that appears” (B xxvi). Things in themselves are not knowable (where knowledge involves some sensory input), but we have to believe that things in themselves exist. This not only follows from the fact that logically, an appearance is always an appearance of something, but it is also supported by what we might call (anticipating the approach of Husserl) phenomenological evidence: it is a fact that I always take appearances to be appearances of independently existing objects. In the absence of any compelling reason to doubt this phenomenological evidence, why would we?
But here is another problem: if I only know objects as they appear to me, then how do I know that I am not alone in this universe, locked in my own little idiosyncratic world of appearances? This is the problem of solipsism. A less drastic possibility, but still highly problematic, is that while other minds exist, they might all “construct” reality in radically different ways. Kant’s answer to these problems is complex. It involves arguing that individual subjectivity is constructed through intersubjectivity: in other words, my own sense of being a knowing consciousness with knowledge and intentions is actually shaped through my interactions with other consciousnesses. Thus, a purely private or singular subjectivity would be impossible. We live in the world with others, and we find when we interact with those others that we are all pretty much “constructing reality” the same way (contrary to the claims of some of today’s wooly-headed postmodernists).
Subsequent German philosophers (the so-called “German Idealists”) would find Kant’s answers to these problems inadequate, and they would seek to overcome his distinction between phenomena and things in themselves, usually by in some fashion eliminating things in themselves. Instead of landing them in subjective idealism or in solipsism, the elimination of things in themselves generally led the Idealists to affirm some version of “objective idealism,” the position (which has roots in Aristotle) that the Being of the world is constituted by ideas that are immanent in the world itself (as opposed to ideas “in a mind”). (I will deal with the German Idealists in one or two future essays.) For his part, Kant initially called his system “transcendental idealism,” using “transcendental” in the sense discussed earlier. This is the position that objects are “empirically real,” meaning that they are founded on intuitions of something independent of our minds, but that those objects, as we experience them, are “transcendentally ideal,” meaning that what these objects are for us is the end result of the constitutive activity of a priori structures.
Now, Kant thought he had made his position quite clear to his readers. So, he was shocked and angered when one prominent early reviewer of The Critique of Pure Reason professed he could not tell the difference between Kant’s position and that of the Irish empiricist George Berkeley, Bishop of Cloyne.
Berkeley was a subjective idealist or what is sometimes called today a “phenomenalist” (not to be confused with a phenomenologist, which is something quite different). He believed that only “ideas” exist, and he used the term “ideas” in the broad manner of the time, as an all-purpose term comprising perceptions (e.g., my perception of the cup on the table), mental images (e.g., my hallucinating a cup or calling it up to imagination), and ideas in the sense of “concepts” (e.g., my general idea of what a cup is). Berkeley held that strict empiricism should result in our affirming that “ideas” are the only objects we are aware of, and so the only objects we can confidently affirm exist. Though philosophers theorize that our ideas are representations of “external objects,” we never directly experience those objects, Berkeley maintained, so an empiricist has no basis for believing in them. We also never directly experience something called “material substance” underlying the perceptible qualities of things. Thus, Berkeley rejects the existence of matter as a mere fiction.
However, this did not land Berkeley in claiming that our experience of the world is an illusion. No, he simply claimed that the world just is our ideas. Esse est percipi, he wrote: “to be is to be perceived.” It is hard to imagine a more brazen formulation of Heidegger’s “metaphysics of presence ” — the hidden will behind the history of metaphysics, whereby Being is construed, in one way or another, as that which is permanently and wholly present to human subjects. Heidegger did not take the bait, however, and says nothing about Berkeley except in passing (probably because he, like many other German philosophers, did not take British empiricism very seriously).
While the world just is my ideas, Berkeley postulated the existence of multiple subjects who perceive similar ideas. But what guarantees that our individual, subjective worlds overlap, if ideas do not “represent” anything outside our minds? And if “to be is to be perceived,” does that mean that when I’m not experiencing the ideas I call “this cup” the cup therefore blinks out of existence? Bishop Berkeley’s answer to both of these questions, unsurprisingly, is to appeal to the supreme being. God exists, and he reconciles and coordinates the ideas held by the different minds, to create one unitary and consistent “world of ideas.” Further, God is constantly perceiving every idea, all of the time, thus nothing ceases to exist just because I myself stop looking at it. In short, God is the constant and eternal dative of constant and eternal presence.
Ironically, Berkeley thus winds up in much the same place as Leibniz. This is a real oddity, since they begin from diametrically opposed methods. Yet both affirm phenomenalism, and both drag God in as a deus ex machina to resolve the problems phenomenalism creates. Leibniz is a much more profound and interesting philosopher, but the similarities between the two are truly striking. Might there be some deep, underlying assumption shared by both men, which results in this convergence of their ideas? Indeed there is, and it is the representationalist paradigm.
Despite the fact that both Leibniz and Berkeley explicitly reject the notion that ideas “represent” external objects (at least insofar as those objects are conceived as material), both also buy into the image of the detached subject, existing in a kind of “interior,” inspecting “inner ideas” of which it is directly (and unproblematically) aware. As I have argued in previous essays , it is this duality — the detached, interior subject vs. the oppositional “exterior” world of objects — that is the foundational metaphysical assumption that makes representationalism possible. In effect, both Leibniz and Berkeley eliminate the “out there” of representationalism while preserving the “in here” — completely missing the fact that without the one there cannot be the other.
It is easy to see why Kant was so vexed when he found himself confused with Berkeley. Kant thought he had made it clear that he was no phenomenalist. He had affirmed that the appearances we experience are appearances of something — something that exists “in itself,” in its own right, independent of our experience. To be sure, he had also affirmed that we only know objects as they appear to us. But, again, he had made clear that there is nothing fatally subjective in this, since objects have their origin both in the constitutive forms of the understanding, and in the “matter” of sensibility.
Further, the first Critique had resulted in a thorough-going rejection of the sort of metaphysical speculation Berkeley was engaged in when he abruptly forgot his empiricism and thought he could invoke the existence of God (who never appears to the senses). Of course, the major target of Kant’s critique of metaphysics was not Berkeley (whose work he barely knew) but rationalists like Leibniz. Kant’s thesis about the role of a priori structures in constituting experience served as the foundation for his critique of metaphysics. The exclusive role of those structures, he insisted, was to give form to the matter of sensibility. Famously, Kant said that “Thoughts without content are empty, intuitions without concepts are blind” (B 75, A 51). Taking the second statement first, this means: intuitions (sense data) without the structural activity of the a priori categories will not give us the experience of an object; but, conversely, when those categories are utilized in the absence of sense data, they give empty . . . what? Answer: empty metaphysical speculations.
The rationalists disengaged categories such as substance and accidents, cause and effect, possibility, existence, and necessity from their legitimate role in structuring intuition in order to use them to reason about noumenal objects like God and the soul, objects which are in principle unobservable. In other words, they misused the categories (as well as logic) to speculate about objects that can never appear to us. Is it any wonder that they all disagree? The truth is that, in a certain sense, they are not talking about anything. Kant employs a wonderful image to describe the folly of the metaphysicians: “The light dove, cleaving the air in her free flight, and feeling its resistance, might imagine that its flight would be still easier in empty space. It was thus that Plato left the world of the senses, as setting too narrow limits to the understanding, and ventured out beyond it on the wings of the ideas, in the empty space of the pure understanding” (A 5, B 9). This criticism of metaphysics is the primary purpose of Kant’s first Critique, as well as the short book he wrote when he found that the first book had been misunderstood, Prolegomena to any Future Metaphysics that Will be Able to Come Forward as a Science (1783). However, more celebrated today is Kant’s exploration of transcendental subjectivity, on which, as I have indicated, the critique of metaphysics is based.
From the foregoing brief discussion of Kant’s agenda in the first Critique, we can see that there are points of convergence between his thought and Heidegger’s. After all, Heidegger’s entire career was devoted to a critique of metaphysics, which he thought had had a baleful influence (a view Kant shared). It thus seems that Heidegger should have seen Kant, the first thinker in the history of philosophy to pose a serious challenge to metaphysics, as a natural ally. Did he? Or did Heidegger see Kant as invested in the same metaphysical tradition that he critiques? We will explore this question in the next essay.
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  I am using Norman Kemp Smith’s translation of The Critique of Pure Reason (New York: St. Martin’s Press, 1965). Reference is to the marginal pagination, standard in all editions of the Critique. “A” refers to the pagination of the first edition (1781), “B” to the second edition (1787). Though this may at first seem confusing, a glance at any edition will show that is easy to locate passages this way.
  I am greatly simplifying what is, in fact, an extremely complex issue in Kant interpretation. There is a major controversy over whether Kant’s “a priori rules” have the status of logical rules, or of psychological functions. For a thorough treatment of this subject, see Frederick Beiser, German Idealism: The Struggle Against Subjectivism (Cambridge, Mass.: Harvard University Press, 2002), 163-79.