Kant, Immanuel (1724–1804)

DOI: 10.4324/9780415249126-DB047-2
Version: v2,  Published online: 2004
Retrieved July 25, 2024, from

8. The illusions of theoretical reason

In the ‘Transcendental Dialectic’, Kant argues that the doctrines of traditional metaphysics are illusions arising from the attempt to use the categories of understanding to gain information about objects that are inaccessible to our forms of intuition. What makes such illusions inevitable is the tendency of human reason to seek the unconditioned, that is, to carry a chain of ideas to its assumed completion even when that lies beyond the bounds of sense. For example, understanding may tell us that wholes consist of parts, and sensibility may allow us to find a smaller part for any given whole; but only reason suggests that decomposition into parts must come to an end in something absolutely simple, something we could never perceive by sense. In its practical use, reason may produce ideas of the unconditioned, such as the idea of the universal acceptability of maxims of action, which do not tell us anything misleading about the world because they do not tell us anything about how the world is at all, only how it ought to be; but in its theoretical use reason appears to tell us things about the world that cannot be confirmed by our senses or are even incompatible with the forms of our perception.

This diagnosis of metaphysical error makes good sense of Kant’s procedure in the ‘Antinomy of Pure Reason’, where he presents a series of conflicts between the form and limits of sensibility as structured by the understanding, on the one hand, and the pretensions of unconditioned reason, on the other. In early sketches of the Dialectic (Reflections 4756–60, 1775–7, 17: 698–713) Kant’s diagnoses of all the illusions of traditional metaphysics took this form. In the Critique, however, Kant singled out some metaphysical beliefs about the self and about God for separate treatment in the ‘Paralogisms of Pure Reason’ and ‘Ideal of Pure Reason’. These sections offer powerful criticisms of traditional metaphysical doctrines, but require a more complex explanation of metaphysical illusion than the single idea of reason’s search for the unconditioned.

In the ‘Paralogisms’, Kant diagnoses the doctrines of ‘rational psychology’ that the soul is a substance which is simple and therefore incorruptible, numerically identical throughout the experience of any person, and necessarily distinct from any external object (this is how he reformulates the Fourth Paralogism in the second edition (B 409)), as a tissue of ungrounded assertions mistaking the logical properties of the representation ‘I’ or the concept of the self for the properties of whatever it is in us that actually thinks (A 355/B 409). Kant’s criticism of the traditional metaphysics of the soul is convincing, but does not depend on reason’s postulation of the unconditioned; instead, Kant’s demonstration that these doctrines arise from confusion between properties of a representation and what is represented showed that they were not inevitable illusions by destroying their credibility once and for all.

The four metaphysical disputes that Kant presents in the ‘Antinomy of Pure Reason’ are often read as straightforward conflicts between reason and sensibility; but Kant characterizes them as disputes engendered by pure reason itself, so a more complex reading is required. In fact, both sides in each dispute - what Kant calls the ‘thesis’ and ‘antithesis’ - reflect different forms of reason’s demand for something unconditioned, and what conflicts with the limits of sensibility is the assumption that these demands give rise to a genuine dispute at all. Kant again uses the contrast between ‘mathematical’ and ‘dynamical’ to divide the four disputes into two groups, and resolves the disputes in two different ways.

In the first antinomy the dispute is between the thesis that the world has a beginning in time and a limit in space and the antithesis that it is infinite in temporal duration and spatial extension (A 426–7/B 454–5). In the second antinomy, the dispute is between the thesis that substances in the world are ultimately composed of simple parts and the antithesis that nothing simple is ever to be found in the world, thus that everything is infinitely divisible (A 434–5/B 462–3). In each case, thesis and antithesis reflect reason’s search for the unconditioned, but in two different forms: in the thesis, reason postulates an ultimate termination of a series, and in the antithesis, an unconditional extension of the series. In these ‘mathematical antinomies’, however, Kant argues that neither side is true, because reason is attempting to apply its demand for something unconditioned to space and time, which are always indefinite in extent because they are finite yet always extendible products of our own cognitive activity (A 504–5/B 532–3).

In the two ‘dynamical antinomies’ Kant’s solution is different. In the third antinomy, the thesis is that ‘causality in accordance with laws of nature’ is not the only kind of causality, but there must also be a ‘causality of freedom’ underlying the whole series of natural causes and effects, while the antithesis is that everything in nature takes place in accord with deterministic laws alone (A 444–5/B 462–3). In the fourth antinomy, the thesis is that there must be a necessary being as the cause of the whole sequence of contingent beings, either as its first member or underlying it, while the antithesis is that no such being exists inside or outside the world (A 452–3/B 480–1). Again, the theses result from reason’s desire for closure and the antitheses result from reason’s desire for infinite extension. But now the theses do not necessarily refer solely to spatio-temporal entities, so the claims that there must be a non-natural causality of freedom and a necessary being can apply to things in themselves while the claims that there are only contingent existents linked by laws of nature apply to appearances. In this case both thesis and antithesis may be true (A 531/B 559). This result is crucial to Kant, because it means that although theoretical reason cannot prove that either freedom or God exist, neither can it disprove them, and room is left for the existence of freedom and God to gain credibility in some other way.

The last main part of the ‘Dialectic’ is Kant’s critique of rational theology. Here Kant reiterates his earlier critique of the ontological argument as well as his claim that the arguments for the existence of God from contingency and from design - the ‘cosmological’ and ‘physico-theological’ proofs - can only get from their ideas of a first cause or architect to the idea of a perfect being by the supposition of the ontological argument, and thus fall along with that. But he now precedes this argument with a critique of the argument for God as the ground of all possibility that he had earlier accepted: the very idea that there is an ens realissimum, an individual being containing in itself the ground of ‘the sum-total of all possibility’ (A 573/B 602), is another of the natural but illusory ideas of reason.

Kant does not, however, conclude the first Critique with an entirely negative assessment of pure reason. In an appendix to the ‘Transcendental Dialectic’, he argues that even though reason in its theoretical use cannot yield metaphysical insight, it does supply us with indispensable ‘regulative’ principles, of both the maximal simplicity of natural laws and the maximal variety of natural forms, for the conduct of empirical research; and in the ‘Canon of Pure Reason’, he argues that practical reason supplies an ideal of the highest good, the union of virtue and happiness and ultimately the union of freedom and nature, which is indispensable for moral conduct, not as its direct object but as a necessary condition of its rationality - which in turn gives ground for the practical postulation if not theoretical proof of the existence of God. Kant expands on both of these ideas in subsequent works (see §11 and §13).

Citing this article:
Guyer, Paul. The illusions of theoretical reason. Kant, Immanuel (1724–1804), 2004, doi:10.4324/9780415249126-DB047-2. Routledge Encyclopedia of Philosophy, Taylor and Francis,
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