This paper explains how P. F. Strawson draws upon Kant’s critique of rational psychology and his rejection of the Cartesian theory of the soul in the Paralogisms to support his verificationist interpretation of Kant’s philosophy. In Strawson’s view, the entirety of Kant’s critical philosophy is grounded in principle of significance. He regards Kant’s ingenious achievement in the Paralogisms as his refutation of rational psychology, which assumes that by means of introspection and philosophical reflection, it is possible to prove the existence of a simple, immaterial substance possessing personal identity. Strawson shows how Kant, on the basis of the principle of significance, attacks this theory and denies the possibility of such knowledge, since any cognition of the “I,” as the “pure form of experience,” has its roots in the “unity of consciousness,” which necessarily requires its connection with an objective external world. Thus, the thinking “I” is not a real entity; rather, in accordance with the principle of the unity of apperception in the Transcendental Deduction, it must be understood as a “synthetic function” in the process of cognition. The thinking “I” is a phenomenon for which the empirical conditions of cognition—required for regarding it as a real thing—are not fulfilled; it cannot be a thing in time and space. Instead, our conception of it is a product of the cognitive system itself: we unify objects in the imagination, and because our conception of ourselves is also unified, we confuse “the unity of experience” with “the experience of unity.”