Kant’s Critique of Theoretical Reason

Part IV: The Theoretical Restriction of Reason and Traditional Metaphysics (Overview)

  • Synthetic a priori judgments and the conditions for the possibility of experience
  • Applicability of a priori principles to empirically given objects
  • Restriction of determinate application of principles to real or possible empirical objects (phenomena)
  • Demands of reason and unconditioned conditions
  • Contributions of sensibility, understanding, and reason to the possibility of synthetic a priori cognition of nature
  • Reason and Traditional Metaphysics

The Theoretical Restriction of Reason and Traditional Metaphysics

In the Critique of Pure Reason, Kant looks at each of our cognitive capacities and explains its role in synthetic a priori judgments. This allows him to explain the possibility and legitimacy of synthetic a priori judgments in a general way that applies to geometry, to physics, and to metaphysics. The key to understanding the legitimacy of these kinds of cognition is noting the role these capacities play–both individually and in functional relation to one another–in providing the formal or transcendental conditions for the possibility of experience. In this way, Kant can secure the claim of objective necessity (rather than of merely subjective custom or habit) for basic principles of reasoning concerning real existence and matters of fact in physics and in metaphysics; e.g., every effect has a cause, in all change something is permanent. We can presuppose the objective legitimacy of these principles for our reasoning, but not because they are intuitively clear and distinct through the natural light of reason; and not because we have previously secured knowledge of a perfect being who illuminates our intellect with supernatural light. We are secure in their use because we recognize that, without this use, we would not be able to have any cognition of objects whatsoever, including the ‘garden variety’ cognition that we gain through common life and everyday experience. So, like Hume, Kant connects these principles of reasoning to common life and experience. Unlike Hume, however, he sees them as conditions for the possibility of experience, rather than as products of actual experience.

This method of securing the objective status of the principles–or their applicability to objects of experience despite their source in the cognitive functioning of our minds–brings with it a significant limitation. The objects that we think through concepts of the understanding and that we make determinate judgments about by appeal to these principles have to be objects that can be given to us in some possible experience (sensible objects or phenomena). If we abstract from all conditions for the possibility of experience, we no longer have any intuitive counterparts to our concepts that we can appeal to in making synthetic a priori judgments. So, what these things may be like in-themselves, and what real relations they may have to other things-in-themselves, is not something we can determine. We can think non-empirical objects indeterminately (e.g., as grounds for the phenomena of actual and possible experience), but that mode of thinking does not constitute objective cognition of the existence and properties of non-empirical objects like the soul, the world system, and God.

Our reason is a faculty that pushes us to seek the conditions for given things, and then ask questions about these conditions. Are these conditions themselves conditioned by something else? If so, what are these conditions, etc. If we perceive something, we take it to be an effect of some cause or causes, and we try to find out what these causes are. Once we discover the immediate causes, we ask about whether those causes have causes, etc. Reason demands us to carry out this process, and insists that we don’t stop until we arrive at some ultimate condition that requires no further conditions. Only then, do we have a totality of conditions.

The totality of conditions for any given thing, however, is never given to us all at once as a single thing. Reason projects this totality as something that is given (in itself) and that could, potentially, be given all at once as a single thing to some mind (that would have to be incomparably greater than our own). In our reasoning from experience, we make use of a synthetic a priori principle that the understanding prescribes to itself; namely, if the conditioned is given, then so is the condition. Reason generalizes here to the more ambitious principle: if the conditioned is given, then so is the entire series of its conditions. The representation of some totality as the ultimate given condition for any and all given individuals of some kind is an idea of reason. These ideas are crucial for our systematic investigation of nature (natural philosophy), but their use in this regard neither depends on, nor constitutes, cognition of the real existence and determinate properties of the objects we think through these ideas. We think them as relatively unconditioned (i.e., the soul, the world system) or absolutely unconditioned (God) conditions for the possibility of the objects of our experience, but we cannot use experience or a priori reasoning to justify any claims to determinate knowledge concerning the existence and characteristics of objects that exist in themselves, are conceived through themselves, and correspond to the ideas we take to be representations of them.

Cognitive Capacities and Roles in Synthetic a priori Judgments     

Sensibility contributes the purely formal intuitions of space and time. These are necessary for the synthetic construction of mathematical objects, like triangles, which is what allows us to provide a priori demonstrations for the particular claims we make about these objects in arithmetic and geometry. Although these intuitions are necessary for judgments of this kind, they are not alone sufficient.

Understanding contributes the forms of all judgments about any kinds of object whatsoever—or the basic concepts (categories) that enable us to subsume particulars under general concepts (e.g., this is a triangle, or this is water) and to further determine the concept of the subject term of the judgment through some particular predicate term (e.g., this triangle is a right triangle, this water is cold). These categories, together with the pure intuitions of space and time, allow us to have a priori cognition concerning the formal features of objects of experience (phenomenal substances); e.g., they will be ‘given’ to us through our sensible intuition—if they are objects of outer sense, they will be somewhere in space and will endure through some period of time; they will be subsumable under the most general categories of quantity (extension) and quality (intension), and they will be determinable through categories of relation (substance and accident, cause and effect, reciprocity) and categories of modality (possibility, existence, necessity). These categories, or these general functions of judgment, are required for the unity of consciousness (or unity of apperception) in which all my actual and possible representations and acts of judgment can be referred both to myself as the subject of these representations (I think ‘S is P’) and to some object (this S, which may or may not be identical to myself, is also P). This is a more detailed way of articulating why Hume’s view of the mind is inadequate—it a) cannot account for the possibility of experience and b) tries to derive from experience certain representations that are necessary conditions for experience. It is also a way of articulating how our a priori geometrical representations of bodies (i.e., in terms of quantities of extension) are relevant to our study of the actual, empirically given, bodies we come across in nature. If we understand the Leibnizean point that extension is not an attribute of metaphysically ultimate substances (things-in-themselves) but is an essential feature of any enduring object of our external sense experience (phenomenal substance), then the relation between our purely geometrical thinking in terms of the possibility and essence of bodies, on the one hand, and the real, existing objects that we know about through the senses, on the other, can be understood:

  • We can know a priori that any body we come across in experience will be extended in space, because spatial extension is a condition for the possibility of our experience of bodies. (Quantity = extensive magnitude)

We can go beyond pure geometry in determining what is essential to bodies by considering that actual sensible awareness of something (in contrast to imagining something as being spatial) involves perceptions that also have some degree of intensive magnitude–or, to borrow from Hume, they are forceful and vivid to some degree:

  • We can know a priori that any body, in addition to extensional magnitude, will also have some intensional magnitude; i.e., it will fill the space through which it is extended to some degree or another, again, because this is a condition for the possibility of our experience of bodies. (Quality = intensive magnitude)

Beyond that, we can go beyond the purely mathematical representation of bodies (as extended things) to the dynamical representation of them as co-existing with other bodies in space, through time: providing the enduring grounds of their properties (substance), and as causes relative to changes in state in other bodies (causality) (Relations); by appeal to which we can distinguish between judgments concerning bodies that express physical possibility, physical actuality, and physical necessity (Modalities)

Although pure sensible intuitions (space and time) and pure concepts of the understanding (both mathematical and dynamical concepts) are necessary conditions for the possibility of experience, they alone are not sufficient.

Reason contributes the idea of an unconditioned totality of conditions for anything that is thought as being conditioned in some way. This leads to ideas of the soul and the world. It also leads to two, very different, ways in which we can think about the objects we posit through the use of these ideas: 

  • indeterminately as substantial grounds of phenomena = the whatever it is that provides the ontological basis for the appearances of inner sense (soul) and the appearances of outer sense (world))
  • determinately as substantial things-in-themselves =  simple substance (soul), or a multiplicity of simple substances (world), that exist in themselves and can be conceived through themselves

The coherent use of reason in theoretical endeavors requires distinguishing these modes of thinking from one another, avoiding the errors that arise when we conflate them, and leaving some of the questions that we would like to answer determinately (e.g., concerning the existence of God and the immortality of the soul) as open questions that our nature prompts us to ask, but does not allow us to answer decisively (in the affirmative or the negative).

Reason and Traditional Metaphysics

Descartes and others want metaphysics to be more than a determination of the basic principles the mind makes use of in reasoning about real existing things (e.g., substance persists through change, every event has a cause, a cause must have at least as much reality as its effect, whatever I perceive clearly and distinctly as belonging to the essence of some being really does belong to its essence, etc.) They want to start with these principles of thinking and use them to move from the existence of things that we perceive to exist to the existence of things that we think exist but that we can never perceive (e.g., God, a world of physical objects). The key to getting there, for Descartes, is the cogito: I perceive myself to exist in any act in and through which I perceive, think, or doubt, that anything at all, of any kind, exists; therefore, I have an allegedly direct representation of myself (intuition) as a substance, and, through my own activities of thinking and willing, as a cause, etc. The causal reasoning grounded here gets me to certainty concerning the existence of God–first, as cause of some given effect (Meditation III), then, as existing necessarilly in and of itself (Meditation V)–and, eventually, a high degree of probability concerning the existence of the world.

Kant argues that the basic principles we make use of have their sources a priori in thinking, but they have their justification for use in our reasoning about real existence and matters of fact by appeal to the possibility of experience. Since the objects we are concerned with in traditional metaphysics are objects that we think of as being beyond the limits of any possible experience, we cannot rely on the basic concepts and principles that are legitimate with respect to any possible object of experience (phenomenon) to say anything determinate about these objects (noumena). The soul, as an object of our inner sensible awareness that we make judgments about through intuitions and concepts, is an object of experience. The soul, as a substance that exists in itself and can be conceived through itself, however, is not. Descartes leads us astray, in Kant’s view, by failing to distinguish clearly enough between what we can conclude legitimately from the experience of the self, according to principles of substance and causality, and what we are tempted to conclude when, in our speculative thinking, we exempt the principles of substance and causality from the conditions for their legitimate employment (i.e., the conditions for the possibility of experience), yet still insist that they can be used to determine the existence and features of objects (i.e., to reason about real existence and matters of fact).    

The idea of the soul is the thought of the totality that provides the ultimate subject of all my actual and possible representational states; i.e., the relatively unconditioned condition of all these states being related to one another and to me as my states. This unity of consciousness is an ultimate principle relative to my experience and to my thinking, so I treat it as something that can also exist in itself, independently of these particular experiences and thoughts, and independently of the particular body in and through which it has these. I can think this consistently (i.e., without contradiction), but I cannot know for certain that the soul really does exist in this way.

The ideas of the world are the thoughts of the totality of mutually related and mutually determining natural substances; i.e., the unconditioned conditions relative to all actual and possible determinate states and natural changes of state within changeable substances. These ideas lead us to questions about whether the conditions we think of as unconditioned in these relations are also themselves unconditioned or whether, instead, there is some further condition for the possibility, existence, and connection of these substances in a world system. This is where the issues arise between naturalism and theism and between necessity and freedom. Kant argues that we cannot decide decisively between these contrasting views solely by appeal to theoretical reason–they involve specific determinate claims about things-in-themselves that we cannot establish with any certainty (either positively or negatively).

Theism concerning the cosmological ideas (ideas of the world) is internally coherent and consistent both with naturalism concerning scientific knowledge of phenomena and with freedom concerning the exercise of the will as a capacity of a thing-in-itself.  Again we cannot demonstrate that it is true by reference to theoretical considerations, but we also cannot demonstrate that it isn’t.

The cosmological ideas then lead our thinking to the Transcendental Ideal or the idea of God, i.e., the representation of some existing thing not simply as transcending the natural world and providing the necessary and sufficient conditions for it, but also as an absolutely unconditioned totality of reality (i.e., a substance that exists in itself absolutely and can be conceived through itself absolutely). According to Kant, this is how we arrive at the idea of God that Descartes, Spinoza, and Leibniz place at the start of the ontological argument. That argument fails to be demonstrative, in Kant’s view, but the idea itself still plays a crucial and positive role in our theoretical endeavors.

Although these ideas do not themselves amount to knowledge of the existence and determinate characteristics of the soul, the world, or God, they do provide us with some of the conditions for the possibility of the kinds of empirical knowledge that we achieve through the natural sciences—they provide us with ideal end points for the progress of our empirical studies in psychology, in cosmology, and in natural history. Beyond that, when understood properly through a systematic critique of reason, they also provide us good reasons for distinguishing between the realm of experience and empirical knowledge (i.e., the natural world qua totality of grounds for all the various phenomena we could, in principle, observe and seek to explain) and the realm of the things-in-themselves that we think both as grounds for these phenomena and as having a mode of existence that is not exhausted by their relation to the observable phenomena they ground; i.e., as substances, or things that exist in themselves and can be conceived determinately through themselves… (just not by finite intellects, like our own, which are constrained to conceive them indeterminately, as grounds relative to the phenomena we observe, rather than directly as individuals given in and through themselves).


Part V: The Practical Extension of Reason and Traditional Metaphysics

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