Kant, Immanuel
Kant's early philosophy of mind included rational and empirical psychologies and offered a solution to the mind/body problem. Later, Kant offered a strong critique of rational psychology and took a broadly skeptical attitude towards knowledge of the soul and the mind/body relation.

To help readers gain the best understanding of Immanuel Kant’s philosophy of mind, this entry concentrates on works from Kant’s early career that are less well-known than his celebrated Critiques. It was in this so-called "pre-critical" period that Kant developed and articulated a substantive philosophy of mind. His critical writings, by contrast, are marked by skepticism and an unwillingness to advance substantive claims about mind. The substantive claims of the pre-critical period are interesting in their own right, and understanding why and how Kant came to reject them affords a deeper understanding of Kant’s mature skepticism.
Kant’s Pre-Critical Philosophy of Mind
In the decades before the publication of the Critique of Pure Reason, Kant was a metaphysical dualist who offered a positive account of mind/body interaction. Thoughts of the True Estimation of Living Forces (1747), his first philosophical work, contains an argument that the mind/body problem presupposed several false and interrelated assumptions, all of which fell under the general view that the essential force of body is vis motrix. Kant argued that the traditional vis motrix view, which was defended by Wolff and other post-Leibnizian German rationalists, appealed to an unexplanatory and metaphysically incoherent conception of force.
Kant’s Pre-Critical Understanding of the Mind/Body Problem
Kant maintained that a number of alleged difficulties with mind/body interaction shared several false assumptions: that bodies possess vis motrix only, that a body can act only by causing motions in itself or something else, that a body can be acted upon only by being moved, and that the moving force of bodies is alien to whatever type of force immaterial substances possess. He believed that these assumptions generated two main difficulties for understanding mind/body interaction. First, if a body can act only by exerting vis motrix, then a body can act on a soul only if it can cause the soul to move. But, Kant objected, such an explanation would do nothing to explain the characteristic effect of matter on the soul, namely the production of representations. If bodily force is a moving force, he concluded, the body's power to produce mental representations is an unfathomable mystery. The second problem is closely related to the first. If bodies can be acted upon only by being caused to move, then the assumption that the essential force of the soul is not vis motrix (but some unknown power) provided no basis for explaining how souls could act on bodies. For these reasons, he concluded, the vis motrix view entails that the nature and possibility of the mind's action on the body are hermetic puzzles that philosophy will never crack.
Kant maintained that God acted to unify our world in such a way that all its finite substances possess an essential force—a vis activa—capable of producing motion in bodies and representations in souls. Unlike Leibniz’s account of vis activa, Kant’s account was compatible with the existence of transeunt or externally-directed forces. Indeed, Kant argued that every change in our world involves the exercise of a transeunt force that acts in accordance with the "divine schema" by which God unified our world.
Kant’s account of embodied cognition in The Universal Natural History
In the Appendix, the third section of the Universal Natural History of 1755, Kant gave an account of the role in cognition of specific actions of the body on the mind. He defended two main claims. The first was the idea that all the soul’s conceptual activity is dependent on sensory material that it receives as the effect of bodily action. The second was that the sluggishness of the body, which is caused by the body’s specific material constitution, impedes the ability of the soul to think.
If cognition is viewed as a succession of mental states, Kant’s claim was that this succession depends causally on a corresponding succession of bodily processes. Specifically, he argued that the body’s sluggishness hinders, degrades, or impedes the succession of states that occur in the soul. Because the succession of states in the soul depends on the succession of states of the body, Kant concluded, the specific character of our bodies’ material constitution affects the character of our cognition. Thus Kant’s account of "embodied cognition" did not merely assert that the quality of the sensory material provided by the body affects the quality of cognition, but he argued that the soul is dependent for any change—and thus for cognition, which involves a temporal sequence of mental states—on the successive states of the body.
Problems with Kant’s early philosophy of mind
Kant came to see that his philosophy of mind was inadequate. Chief among the difficulties was that his account of the divine schema of our world was incompatible with his metaphysical dualism: to exist in our world, Kant argued, all substances must possess attractive and repulsive forces, but attributing these forces to souls implied that they also possessed the same material nature as the physical monads out of which material bodies are composed. This problem threatened to collapse Kant’s metaphysical dualism into a monadological monism.
Kant’s account of the location of the soul with respect to the body generated a second problem that plagued him until the end of the pre-critical period. Kant held that our souls fully penetrate our bodies in the sense that one’s soul and one’s body are located in the same volume of space at the same time. Unfortunately, this contradicted his account of how substances exist in space. According to the divine schema of our world, a necessary condition of a substance being located in space is that it possess a repulsive force and thus impenetrability. Our souls and our bodies can interact only if they are both in our world, but this is true only if both types of substances are impenetrable and thus incapable of existing in the same space at the same time.
What Kant required was an explanation of souls’ locations in space that was compatible with souls being unextended, immaterial substances that could penetrate material bodies. In 1766, when he published Dreams of a Spirit Seer, Kant concluded that he did not possess the philosophical resources to solve this problem. However, in the Metaphysik L1 lectures (mid-1770s), Kant put forward a new understanding of the mind/body problem that centered on the idea that the body is an object of outer sense and the soul an object of inner sense.
The Inner Sense Thesis
Kant drew upon a contrast between inner and outer sense that he first developed in the Inaugural Dissertation of 1770 to revise his early philosophy of mind. One idea, that the soul is an object of inner sense that possesses a virtual presence in space and not a local presence, provided Kant with a new explanation of the mind/body problem and allowed him to resolve a number of the difficulties that had left him perplexed when he wrote Dreams of a Spirit-Seer. Kant connected this "inner sense thesis" to the impenetrability problem in his rational psychology, to the problem of proving that souls do not have the same material nature as physical monads, and to the troubling issue of the soul's location in space.
In Living Forces, Kant had argued that material and immaterial substances were fundamentally homogenous because all substances act by exerting vis activa, but this position effectively caused Kant’s distinction between materiality and immateriality to collapse. By the time he gave the Metaphysik L1 lectures, Kant used the inner sense doctrine to defend the heterogeneity of body and soul: bodies are objects of outer sense, souls are objects of inner sense.
Kant’s new understanding of the soul’s virtual presence in the world was a clear advance over his former doctrine that the soul could act in this world only if it had a local presence in space. Although Kant had not yet adopted the critical view that the soul is not a substance, the inner sense thesis helped him to avoid the contradictions and difficulties of his earlier view.
A new account of embodied cognition
The inner sense thesis also grounded a new account of the tight relation between the soul and its body and of the role of the body in cognition. Kant's account of embodied cognition in the Metaphysik L1 lectures centered on three doctrines, which may be labeled the community thesis, the constitution thesis, and the embodiment thesis. According to the community thesis, the soul and body constitute an especially tight community: my body is the sole conduit for my soul in the sense that my soul is in immediate relation only to my body, and it is in relation to other things only insofar as those things are in relation to my body. This view was enshrined in the embodiment thesis, which stated that there is no mental action where "the body is not come into play" (Akademie Volume 28, p. 259). Thus as he did in the Appendix to the Universal Natural History, in the Metaphysik L1 lectures Kant maintained the "constitution thesis," which stated that the specific constitution of the body affects the constitution of the soul.
However, Kant’s account of embodied cognition in the Metaphysik L1 lectures differed significantly from the account he defended in 1755. Kant asked "from which side is the most to be derived, from the body or from the soul?" (Ak. 28:261). Whereas in 1755 he took himself to possess strong reasons for thinking that the body contributes more to cognition, in the mid-1770s he taught that "we can say nothing about this" (Ak. 28:261). This new understanding of the role of the body in cognition was an improvement over his strong claims in the Universal Natural History, for his defense of the community thesis in the Metaphysik L1 recognized that our embodiment is important for cognition while providing more room for an account of the soul’s spontaneity.
Kant’s Critical Philosophy of Mind
Mind is central to the most famous parts of Kant’s most famous book, the Transcendental Aesthetic and the Transcendental Deduction sections of the Critique of Pure Reason (1781/87). There he argued that it is the mind’s receptive, synthetic, and conceptualizing capacities that make experience possible for us. However, despite the centrality of these claims to his critical system of philosophy, Kant never again attempted to develop a systematic philosophy of mind. Indeed, his often-repeated position was one of skepticism with respect to knowledge of the mind. Resolving this apparent contradiction is among the most important and difficult challenges facing Kant scholarship today. Readers wishing to explore attempts to deal with these challenges may wish to consult in extensive secondary literature on Kant’s critical philosophy, and especially the work by Karl Ameriks (Kant’s Theory of Mind, Oxford University Press 1982), C. Thomas Powell (Kant’s Theory of Self-Consciousness, Oxford University Press 1990), and Andrew Brook (Kant and the Mind, Cambridge University Press 1994). In the remainder of this entry, I focus on the Paralogisms section of the Critique of Pure Reason, which is where Kant developed the interesting and powerful skepticism which dominated his official position in the philosophy of mind.
In the Paralogisms, Kant presented new views on a series of central topics in the philosophy of mind. These topics included the soul’s substantiality, immateriality, and simplicity; its identity, immortality, and freedom; and the soul’s ideality and its relation to embodiment and to the external world generally. He adopts a broadly—and famously—skeptical view, arguing that we can have no positive knowledge about the nature of the mind and rejecting Cartesian claims that we have a privileged self-knowledge. Kant thus turned his back on the positive philosophy of mind that he had struggled to construct in the 1740s, 1750s, 1760s, and 1770s.
Kant's arguments in the Paralogisms can be seen as an application of the theory of judgment he developed in the Aesthetic and Analytic sections of the Critique of Pure Reason. There he argued that a judgment requires both an intuition and a concept and thus that we can have no knowledge of something of which we have no concept nor of something that cannot be intuited in a possible experience. In the Paralogisms, Kant waged a two-pronged attack on knowledge of one's self by arguing (1) that we do not have a proper concept of the self qua self and (2) that we can intuit neither a "phenomenal’ nor a "noumenal" self in any possible experience.
The Paralogisms include Kant’s fascinating discussion of three sources of illusory knowledge of the soul. Each illusion involves the crossing of the limits of possible knowledge and arises from the illegitimate empirical employment of a transcendental concept. He discusses three paralogistic fallacies, namely: (1) the fallacy of conflating a feature of my representation of my self with features of my real self by confusing subjective and objective conditions (e.g., arguing that my soul is a permanent substance because I must always be conscious of the I of apperception), (2) the fallacy of illegitimately applying the doctrine of bivalence to representations by drawing determinate conclusions from an indeterminate representation (inferring that because my representation of myself is not the representation of a complex self, then it must be the representation of a simple self), and, emphasized in the second edition text, (3) the fallacy of inflating analytic into synthetic claims (inflating `my thoughts must have a subject' to `the subject of my thoughts must be simple').
Andrew Carpenter