The questions that Kant inherits and transforms in the Critique of Pure Reason relate to various forms of inquiry. The most important of these concerns metaphysics. The word "metaphysics" has a confusing history, and as every student of intellectual history quickly discovers, it means different things in different times and places. Aristotle's Metaphysics (a title he himself did not use, for a number of writings he himself probably did not group together) covers the meaning of the word "being," the relation between substances and accidents, the prime movers and the gods. In contemporary philosophy, however, "metaphysics" tends to cover such topics as the mind-body problem, free will and determinism, necessity and possibility, and so forth. In the Critique of Pure Reason, Kant undertakes a critique of metaphysics. Before one can evaluate this critique, one needs to understand quite what metaphysics is for Kant.
Kant's overriding concern is to cure philosophy of reliance on immediate flashes of certainty, which he calls "pure intuitions." His cure is to describe the discursive process by which persons make judgments about things. Judgments are made about things through the joining together of things we sense ("sensible intuitions") by following rules for judgment ("concepts"). This process unfolds in time: a person arrives at a judgment after something analogous to deliberation. It is thus not immediate in two ways. First, things are mediated through sense impressions and concepts; and, second, our judgments about them are products of a temporal process. Kant's insistence that our judgments are outcomes of a fallible process rather than immediate intuitions is one of the most significant shifts in modern philosophy, and no theology after Kant can respectably present itself as other than the outcome of such fallible processes of judgment.
Kant is interested in certain kinds of investigation into certain kinds of object. The most important investigations and objects, which dominate the Critique of Pure Reason, are overtly theological. His critique of metaphysics concerns inquiry into three topics: the soul, the world, and God. Kant calls these "ideas of reason" to distinguish them from "objects of experience." He poses the following questions. What are objects of the understanding, and what kinds of investigation are appropriate to them? What are ideas of reason, and what kinds of investigation are appropriate to them? What problems arise when one assumes, falsely, that these objects of inquiry are the same, and that the forms of inquiry appropriate to them are also the same?
Kant's critique of metaphysics is thus not most fruitfully considered a critique of the kinds of investigation that characterize Aristotle's inquiries in Metaphysics. His approach rather resembles Aristotle's in certain respects. The focus of his inquiry is the philosophy which precedes him and which investigates the soul, the world, and God in various ways, not least through appeal to "metaphysics." Before one can evaluate this inquiry, one needs to understand who these predecessors are, and what kinds of inquiry they conduct.
Kant inherits questions from Leibniz about what the soul does in relation to perception, what the world is compared to individual things, and how the world is ordered by God. He also inherits questions about the existence of the soul, the existence of the world (in a particular sense), and the existence of God; he also inherits widely accepted proofs for God's existence. Leibniz's questions about the soul were intended to answer materialist views (like those of Hobbes) which considered human agents as machines. Leibniz argued that to talk of a soul is to talk of something unified, whereas a machine is only ever composite or an aggregate. A soul is something singular and "simple" in the technical medieval sense: it is not divisible into parts, but is one thing. When the soul perceives, it unifies its perceptions. Leibniz' questions about the soul were also intended to answer dualist views which considered human agents as divided into two wholly different substances - thinking substance and material substance (as Descartes had claimed). For Leibniz, a soul is unified, indivisible, and not extended in space.
Kant insists that questions about what the soul "does" can be separated from questions about what the soul "is." Like Leibniz, Kant rejects the dualism and materialism of Descartes and Hobbes. Like Leibniz, Kant is deeply interested in how the manifold of perceptions is unified by the thinking subject. Unlike Leibniz, Kant claims it is not fruitful to treat the soul as if it were an object in the world like the objects which the soul perceives. Kant's argument, in the Critique of Pure Reason, is that talk about the soul is talk about how the thinking subject unifies its perceptions, how the subject's unity persists in time, and how change is registered by something constant in thinking. Such talk is quite appropriate, he thinks. However, for Kant, it is misleading to think that the soul is a thing, that it is an object, and that it can be described or investigated. It is misleading to say that we "have" souls, in the same sense that we have hands. Hands are objects in the world; souls are not. For Kant it is quite understandable - and desirable - that we should describe the thinking subject's unification of its perceptions; indeed he uses Leibniz's technical term "apperception" to describe this. The conclusion that there is some "thing" responsible for that unification is an illusion, however.
Similar considerations apply to "the world" and "God." By "the world," Kant and his predecessors do not mean (as we mean in common speech) the planet Earth. They mean that which contrasts with individuals: it is the whole of things. The world is the totality of objects, considered as a unity. This unity has much in common with the unity of the soul. Leibniz distinguishes between the world considered as the totality of things, and the world considered as the totality of all possible things, and he attributes greater reality to the latter. Kant says of the world what he says of the soul. It is sometimes appropriate and desirable to think of the totality of things as a unity. It is an illusion to think of this unity as a thing. It is not a thing: thinking about "the world" is a way of thinking about how things are unified for us as thinking subjects. The appearance of God in this kind of discussion is at first sight rather puzzling. Why should the creator of all things, the God of Abraham, Jacob, and Moses, or the Holy Trinity, appear in a discussion about metaphysics? The short answer is that this God doesn't, quite. Kant, inheriting a series of debates from Spinoza and Leibniz, is not primarily thinking about God in relation to the Bible or to worship, but to the deus sive natura (God/ Nature) of Spinoza or the ens realissimum (most real being) of Scholastic philosophy. Leibniz is greatly interested in God as creator in a way that Kant is not; whereas Leibniz considers the ways in which order in the world relates to God's activity as creator, Kant is more interested in what kind of unifying role a particular notion or ideal, "God," plays for the thinking subject. Just as the soul is a way of talking about how the subject unifies its perceptions, and the world is a way of talking about how everything that there is can be considered as a unity or totality, so God is a way of talking about the totality of possible judgments about objects. The ens realissimum is the unity of thinkable objects and their possible predicates. Just as the unity of the thinking subject should not be reified into a "soul," and the unity of appearances should not be reified into a "world" that is an object, so the unity of objects of thought in general should not be reified into a "God" that is a thing.
A pattern is emerging. Kant's critique of metaphysics is a critique of ways of talking about the unification of particulars by and in thought. The "soul," the "world," and "God" are not arbitrarily chosen topics. The kinds of unification they represent are the three basic kinds of unification performed by human thought. They are, moreover, ways of thinking about unification, rather than naming things that exist.
Kant does not merely seek to identify the illusion of thingness or thinghood that attaches to the "soul," the "world," and "God." He is also interested in the kinds of investigation that accompany them. It is obvious that he encourages and indeed conducts sophisticated investigations of his own. His point is that one must recognize different kinds of investigation and not confuse them. Things in the world call for a certain kind of investigation. There were two available models for investigation in Kant's time: natural philosophical investigation (what in English we call "science") and historical investigation. Both were candidates as a paradigm for scientific thinking in the eighteenth century. David Hume chose historical investigation; Kant chose natural philosophy. Because of this choice he confronted a problem. It was obvious to him that natural philosophy cannot be the model for thinking about unity, because natural philosophy investigates particulars rather than their totality. Kant thus articulated a different kind of investigation which he called "transcendental philosophy." For Kant, it is vital not to confuse the two kinds of investigation. To investigate God as if God is an existing object on the model of natural philosophy, or to try to prove the existence of God using arguments that belong in natural philosophy, is to produce illusion. Other investigations, however, are quite appropriate. To investigate how it is that the unity of objects of thought in general functions in our ways of thinking is highly desirable. The important thing is not to mistake one kind of investigation for another. Just as Aristotle distinguished investigations looking at things in the world and investigations into being qua being, so Kant distinguishes natural philosophy and transcendental philosophy. In Aristotle's works, the latter kind of investigation is called "Metaphysics," but for Kant "metaphysics" means something rather different: it means forms of inquiry which confuse "things" with "unity."
With respect to "things," Kant has in mind two deficient modes of philosophical investigation. The first he associates with Locke. It is the tendency to treat sensible conditions for human knowing as if they are conditions for objects' existence. In other words, epistemic conditions (sense) are mistaken for ontic conditions (being). It is falsely claimed that sense directly reveals things. Kant's cure for this is to show the limits of sensibility: it is this function that "noumena" discharge, as we shall see. The second he associates with Leibniz. It is the tendency to treat intellectual conditions for human knowing as if they are the conditions for objects' existence. In other words, epistemic conditions (concepts) are mistaken for ontic conditions (being). It is falsely claimed that our ideas directly reveal things. Kant's cure for this is to show that concepts must link up with sense, in a fallible process, rather than assume they are already in preestablished harmony.
While Kant's approach may sound defensible, there is something odd from the perspective of a later reader. The range of meanings of "soul," "world," and "God" are much wider, in the long tradition, than merely the unity of the thinking subject, of appearances, and of objects of thought in general. When we speak of someone as "soulless" or the world as "creation" or of God as "creator," it is not at all obvious that unities (of any kind) are in view, nor that such usages are mistaken. There are other connections between these terms. The soul might be thought of as a point of contact or some kind of analogy with divine action. The world is created by the creator. The soul, the world, and God might be thought of as in an economy of grace. These are respectable uses, and it is not obvious when reading medieval or modern theology that they are riddled with illusion or confusion over modes of investigation. It is thus important to notice that Kant's critique of metaphysics involves a contraction of the range of meanings and usages of the key terms under discussion, and that this range is narrower than it is in Leibniz - for example, where Leibniz speaks of God as creator.
The interpreter of Kant thus requires some subtlety. On the one hand, Kant makes significant headway in overcoming the one-sidedness of Locke and Leibniz. Neither sense (Locke) nor concepts (Leibniz) are by themselves enough to produce judgments of the form "This x is a y." For these prior thinkers, we do not need to judge it at all, because in a sense we already know that this x is a y. Kant produces an account of judgment in which concepts must be combined with sense. Indeed, Kant calls concepts "rules for judgement," and sense "conditions for understanding." The Critique of Pure Reason has, as one of its important tasks, an account of how the human agent spontaneously treats sense data using concepts, in a fallible process that yields judgments that may be true or false. Human judgments (a) are the product of a process and (b) should not be mistaken for truths about the world. Kant thus attempts to cure habits of thought which treat judgments as immediate intuitions of truth. On the other hand, Kant displays an emphatic tendency to ignore well-established ways of thinking about the soul, and about God in particular, in favor of significantly narrowed concepts. The effect is that certain topics, such as the relation between divine creativity and human action, largely disappear from view. Leibniz had wondered, in 1714, what the relationship between nature and grace looked like when considered with modern categories of thought, especially the notion of the unifying "I." Seventy years later, Kant displays almost no interest in this question.
Many theologians consider that Kant's claim that God is only an "idea of reason" is one of his most serious shortcomings. This is perhaps to ignore the bigger problem. Kant's view that God is an idea of reason is a consequence of shrinking the scope of "God" to the ens realissimum, and then glossing the latter as the unity of all possible objects and their predicates. Kant acquires this usage from the late Scholastics and above all from Spinoza. For the Scholastics (roughly speaking, thinkers who came before Descartes), this way of speaking was one of many ways of talking about God. For Kant, in this context, it comes to exhaust what "God" means. If Kant is merely claiming that this unity is an "idea of reason," there is little cause for complaint. When this unity is named "God," however, and when the scope of this term shrinks significantly, certain important theological questions become meaningless, and it is the accompanying disappearance of the question of the relationship between nature and grace that should motivate the theologian's most serious complaints.
It is in the light of this kind of interpretation that one makes best sense of Kant's remarks about the "thing in itself" and the infamous split between "noumena" and "phenomena." When Kant is discussed by theologians, these technical terms often play a central role. It is important to remember that Kant is trying to repair the one-sidedness of "empirical idealism" and "transcendental realism." Empirical idealism is the claim that the only thing we have immediate access to is our ideas. This is commonly associated with Descartes. Transcendental realism is the claim that how things appear to us is how they really are. This is commonly associated with a wide variety of pre-critical philosophers, including Leibniz and Hume. Both rationalist (Leibniz) and empiricist (Hume) philosophies fail to consider that how things appear to us might be distinguished from how they really are.
Kant claims that we can consider an object in two ways. We can consider it independently of how we cognize it, or we can consider it as it appears to us when we judge sensible intuitions by means of concepts. When we consider an object as it appears to us, we have at least three distinct aspects in play. There are the sensible intuitions, the concepts, and the act of judgment. Sensible intuitions can be distorted (our eyesight may require correction); concepts can be poorly grasped (we may need to learn the rules better); judgment can slip up (we may need to learn to be better judges - something Kant thinks is formidably difficult, if not impossible). There is ample room for error, and any particular mistake may be the consequence of a problem with any one of these aspects, or some combination of problems. When we consider an object independently of our judgment, none of these aspects is in play. No sense data are available (because there is no subject to sense); no concepts are available (because there is no rule-following agent); no judgment is made (because there is no judge). To consider an object in this way, "as it is in itself," is very minimal.
How should one interpret Kant here? Perhaps he is saying that there are two objects. There is a "thing in itself," which we cannot know, and there is an appearance, which we can know. On such a two-object or "two-world" view, Kant's task will be to show how these two objects relate to each other. Worse still, Kant will need to explain how he knows that we cannot know the thing in itself, and how he knows where to draw the limits on what we can and cannot know. But perhaps he is saying that there is only one object, but it is considered in two ways. Or it can be thought of "as it is in itself," independently of sense, concept, and judgment. It can be thought of "as it appears," as the product of sense, concept, and judgment. On such a "two-aspect" view, Kant's task will be to show that thinking of objects as they appear is not identical to thinking of objects independently of how they appear. Kant's strongest critics tend to attribute a two-world view to him; his strongest defenders tend to attribute a two-aspect view. The matter cannot be settled by brute appeal to his texts, as Kant offers material to support both interpretations. In this chapter, I have assumed that the two-aspect view produces a richer and more defensible interpretation of Kant. This question is, however, crucial for theology, as discussions of the thing in itself lay the foundation for denying - as Kant does - that we can "know" God.
Similar considerations apply to the terms "noumena" and "phenomena." Again, Kant's concern is to cure the philosopher of one-sidedness, whether rationalist or empiricist. There are objects of knowledge: these are the products of sense data judged according to concepts. There are also ideas of reason: these are products of thinking that arise almost naturally because of how we reason. Kant distinguishes between "understanding" and "reason" in this connection. Understanding is the product of sense data, concepts, and judgment.
The philosopher can pay attention, however, to the principles at work in such understanding. There is a pattern to how we judge sense data according to concepts, and these patterns or principles can be mapped or codified. This mapping or codification Kant calls "reason." As concepts are to understanding, so principles are to reason. Concepts are rules for judgment (of sense data). Principles are patterns of understanding. Understanding unifies appearances. Reason unifies rules of understanding. In other words, understanding orders our perceptions, whereas reason orders our thinking. It is in this debate that the phenomenon and noumenon belong. Kant insists that "knowledge" is a matter of understanding, not of reason. To know is to know an object by judging sense data by means of concepts. Reason displays the patterns of knowing, but it does not yield knowledge itself. We can juggle concepts, clarify concepts, map concepts, order concepts, and so forth. But this (quite legitimate) activity is distinct from knowing things. Where there are sense data judged according to concepts, the products are phenomena. Where there are concepts considered independently of sense data, that is, where there are no judgments to be made, the products are noumena. A noumenon is a product of reason. The "thing in itself" is a noumenon; so is the soul, and so is God. In each case sense data are lacking, and no object appears. Indeed, the confusion of the "thing in itself," or the soul, or God with an object of knowledge is precisely the problem that sections of the Critique of Pure Reason seek to solve. Kant does not reject noumena in favor of phenomena. He rejects conflating them. Considering noumena draws attention to the problems that arise when one tries to conjure knowledge out of reflection on how agents think. Put differently, noumena might best be viewed as a teaching aid or a therapeutic tool rather than a class of object in the world or representations in the mind. Because noumena are products of thinking independently of sense data, the only way one could "know" a noumenon would be through direct intellectual intuition. However, as Kant insists tirelessly, humans do not have direct intellectual intuition. We judge sense data using rules/concepts. For us, knowledge is a fallible process and if we have flashes of insight, those flashes are not immediately self-confirming. More importantly, we only have "knowledge" (in Kant's sense) of a sensible object. We don't "know" concepts or products of reason, although we use them when we know "things."
Kant's critiques of arguments for the existence of God are also best viewed in this light. Kant's root objection is to intellectual intuition: to any claim that one has immediate knowledge of an object independent of its being determined as an object by the subject, through the synthesis of sense data and concepts. Any process which produces an object of knowledge is either an act of the understanding or an illusion caused by the exercise of reason. Proofs for the existence of God are exercises of reason, in Kant's sense, and they claim to produce objects of knowledge. They are thus illusions, for Kant. It is vital to appreciate what questions and answers Kant takes the classic proofs for the existence of God to pose and provide. The ontological, cosmological, and design arguments do not ask the question "Does God exist?" but "Can God's existence be inferred?" Their answers are, in each case, "yes," but with different reasonings. The ontological argument takes many forms; Kant is concerned with the argument associated with Descartes and Leibniz. The argument goes like this:
1. Existence is a perfection (it makes something so good that it cannot be made better).
2. The ens realissimum is the most perfect being, by definition.
3. The ens realissimum is possible.
4. Therefore, the ens realissimum is actual.
The first three claims are premises; the fourth claim is a logical inference. If the ens realissimum did not exist, this would mean that it was not perfect (which contradicts 2), because to be perfect is to exist (which follows from 1).
To tackle this argument, one has to either reject one of the premises or expose the inference as fallacious. Kant rejects the first premise. He denies that "being" is a real predicate. It is important to note that Kant does not deny that being is a predicate: he affirms that being is indeed a predicate. He denies it is a real predicate. "Real" here has a technical meaning. There are two kinds of predicate in play here, "real" predicates and "logical" predicates. A real predicate is a property which makes something what it is. If I say, "The tomato is red" or "The tomato is yellow," the predicates red and yellow make the tomato what it is: a red or a yellow tomato. Red and yellow are real predicates. If I say, "The red tomato is possible" or "The yellow tomato exists," the predicates "is possible" and "exists" do not make the red or yellow tomatoes what they are. "Possible" and "existing" are logical predicates. They are "modal," relating to possibility, actuality, and necessity. If it is objected that logical predicates are real predicates, then "The tomato is red and exists" has two real predicates, "red" and "exists": these make the red existing tomato what it is, and that would mean that the red tomato exists necessarily. Most proponents of the ontological argument do not claim that red tomatoes exist necessarily. To do so would be to do away with modal logic completely, because there would no longer be any point talking about possibility, actuality, and necessity. Everything that exists would exist necessarily, and everything that does not exist would necessarily not exist. Proponents claim that only God exists necessarily. As a result, in Kant's view, they must admit that the first premise does not hold true in all cases. Once the first premise is withdrawn or qualified, the argument collapses.
Kant's critiques of the cosmological and design arguments are also closely woven into his account of cognition. They will not be rehearsed in detail here. The main point is that both the cosmological and design arguments fail to observe Kant's rule that what one can say about the world of sense and judgment cannot unproblematically be transplanted to the world of principles and reason. Both arguments engage in precisely that transplantation, and are thus strongly to be resisted. In addition, the cosmological argument is held to depend on the definition of the ens realissimum. The ontological argument starts with it. The cosmological argument finds its way to it - at the point where it tries to identify the necessarily existing first cause with the ens realissimum. If one were to think about names of God rather than concepts of God (where concepts "capture" their object), the proof (and Kant's critique) might look rather different.
It is vital to remember that Kant is not criticizing the claim "God exists." He is denying that the claim "God exists" can be defended using formulae such as the ontological and cosmological arguments. As with nearly all his transcendental arguments, Kant is interested primarily not in the truth of statements, but in whether they can be mounted convincingly in public. As we shall see, Kant strongly believes the claim "God exists" can be defended publicly in the context of moral reasoning. It is the arguments Kant contests, not the truth of the claims.
Kant's critiques of the proofs for the existence of God are part of his transcendental idealist cure for the errors that arise when one treats reason as the same as the understanding. He is interested in varieties of "transcendental illusion" rather than in questions of God's existence per se. This is why he refers elsewhere to unconditioned necessity as reason's "true abyss." This is an arresting description. One may wonder whether Kant thinks there really is this abyss, and reflection on God shows the point where reason breaks down; or whether he thinks that transcendental errors lead one into various muddles, and the fact that faulty reasoning leads to an abyss is a sign that something needs repairing.
It is perhaps the scope of Kant's terms, rather than his arguments, that should arouse the theologian's suspicion. Kant never argues for his account of God as ens realissimum. It is a technical term he inherits, and he simply chooses not to consider any richer set of descriptions, or more imaginative names, of God. Put slightly differently, it may be Kant's presuppositions, not his demonstrations, that produce theological difficulties. If that is so, the most appropriate theological responses will not primarily be a question of exposing fallacious arguments or weak chains of reasoning, but will involve identifying problematic presuppositions, and repairing them. When Kant says that we cannot "know" God, he means that God is not a phenomenon. There are no sense data to be judged according to a concept or rule that produces the claim "This object is God." Yet it is striking that this sense of "knowing" God is distinct from the senses of knowing God that are rehearsed in patterns of prayer and worship. Kinds of knowing associated with friendship, relationship, trust, service, imitation, participation, and the discernment of God's action in history are not forbidden or ruled out by Kant's metaphysical strictures. They simply do not appear at all. Thus, if Kant says, "There is no knowledge of God," and his theological colleague says, "There is knowledge of God," the meaning of "knowledge" may be equivocal in the two cases. If Kant says, "There is no experience of God," and his theological colleague says, "There is experience of God," the meaning of "experience" may likewise be equivocal. To insist that there is knowledge of God or experience of God in Kant's sense is not meaningless; it would, however, be a novel claim quite different from the claims made by prior theologians about what it means to know God.
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