Many philosophers and scientists worked within the framework provided by Plato and Aristotle. St. Thomas Aquinas was an Aristotelian who leaned more toward the “metaphysical,” Baruch Spinoza more toward the “physicalist.” During the early European Enlightenment (17th century), Rene Descartes rediscovered the dualistic conception of mind/body, in which mind was primary. Under the influence of religion, Descartes’ thinking overemphasized the flaws in the Platonic vision of philosophy and science that were meant to be transformed by Spinoza’s monism. But Spinoza’s interpretation of Aristotle was mostly ignored due to the pressures from the Church. Instead, Descartes and the empirical scientists in the tradition of Francis Bacon helped shift the Platonic perspective to be bounded by mind alone. Isaac Newton criticized Cartesian ideas, for Newton matched and deepened Aristotle’s position and also revolutionized his physics. Newton, as Aristotle, had an interest in honestly applying hard science to the questions of mysticism, and he kept physicalism primary in his conceptions.
The Kantian Seed
During the later European Enlightenment (18-19th century), arrived Immanuel Kant, a central figure of modern philosophy and science. Kant was finally able to separate mind from the establishment of the ancients (see Figure 2). Now, Kant’s philosophy was indeed strange when it arrived. I would say that many misunderstand Kant even today. Those who place Kant into the Platonist camp, like Arthur Schopenhauer, miss a crucial point–Kant’s thoroughly materialistic epistemology–his theory of knowledge. Kant did not use his epistemology to prove the existence of metaphysics. Instead, epistemology was the reality for Kant, and knowledge–inseparable from the knower. He would have probably agreed with Protagoras’ claim that “knowledge is sensation”, as there is subjectivism and relativism in judging forms of perception, will, and the representationalist view of reality in the Kantian tradition (his main treatise (COPR), p. 191). Kantian metaphysics was fundamental to Kant’s sensations; space and time were primary, irreducible categories (as for Aristotle), and Kant’s view of sensations and voids, relative and shared spacetime continua, was surprisingly similar to the quantum physicists’ view of particles today (cf. ibid., pp.123, 129, 140, 163f., 174, 193, passim). Objectivists most emphatically hate Kant, for he had attacked the ontological logic of Aristotle and induced the development of dialectical, mathematical, and later symbolic logics, some of which ignore “contraries, subcontraries, or subalterns”, thus allowing a possibility that existence, “perceived” as a collection of particles, may cease to exist.
The Three Together
While Plato was enamored with the beauty of his metaphysical visions, Aristotle had taxonomized philosophic ideas as they referred back to physical reality and believed that, although matter is potential (dynamis, or nascent change) and form is actual (entelecheia, or becoming itself), they are inseparably the same. Kant, on the other hand, sounding like the pre-Socratic dialectician Heraclitus, said that “[o]nly the permanent (substance) is subject to change” (COPR, p. 148). By substance, Kant presumably meant particles that compose matter, or the metaphysics of such particles. Thus, he repeated Aristotle but in a manner that made his idea of the form (i.e., soul, or the thing in itself) secondary (ibid., p.194), and then he even redefined it as substance or thing and allowed to be “changed into nothing” (pp. 236, 241f.). He said that the ideal is impossible to reach, and this led to an infinite regress into conditional matter. This shows that Kant simply wanted to ignore anything inherently spiritual, such as real form, and rather than moving toward comprehending “the unconditioned causality of God,” he turned away and chose the way of “the unconditioned existence, of substance” (p. 329). While Aristotle had integrated his own physicalism with Plato’s metaphysics, Kant flipped Aristotle and accepted only materialism guided by the metaphysical categories he borrowed from him. Kant then reorganized the a priori concepts within his own “synthetic” rationale as inseparable from “analytic” (i.e., empirical) sense perceptions, though the latter were considered by Kant primary (and thus final or actual). In the true spirit of materialism, reason became secondary to primal matter (p. 326).
In the misguided era after Aristotle, rather than accepting or thoroughly understanding Aristotle’s worldview, Kant had decided to reintegrate Platonic rationalism and Aristotelian empiricism in a way that missed many crucial, mystical ideas and thus proceeded to contradict Aristotle’s ingenious integration. The epistemological contents of the mind became the only perceived reality for Kant, and thus he perceived metaphysics in his senses, having “metaphysical” sense-applied (analogous but not limited to the conception of matter as made of Gottfried W. Leibnitz’ “monads”). Philosophers affected by the Kantian tradition (such as Friedrich Nietzsche and Arthur Schopenhauer, Karl Marx and Vladimir Lenin, and Adolf Hitler through G.W.F. Hegel, all of whom were mixing Platonic “idealist” in Kantian “idealistic” in increasing quantities, respectively) similarly abandoned Aristotelian realism/mysticism, his views of the emotional soul and God, and those simply became meaningless beliefs due to the deficient (for its deontological centeredness) foundation of Kantian ethics.
Rand and I
Although I understand these philosophers differently from Peikoff, I agree with Peikoff’s evaluations of them in his DIM Hypothesis. Peikoff correctly describes Plato as a misintegrator and his philosophy’s determination in science by Albert Einstein, Aristotle as an integrator and his philosophy’s extension by Isaac Newton, and Kant as a disintegrator and his philosophy’s determination in quantum physics. Peikoff has covered the basics, but he has failed to show how Rand’s philosophy is fitted within this historical review of philosophy. Instead, I will show how Rand may fit into the presented schema next week.
 In a stark contrast to Plato, I am calling Kant a master materialist (i.e., scientific epistemologist) rather than a physicalist. Thanks to Kant, there are all the branches of materialism we have today (even if a few of them seem to peculiarly disagree with his original views — a disagreement upon specific ideas rather than a complete philosophy). Kant is in the atomistic tradition of Democritus, with whose “nothing exists except atoms and void” he would have agreed (cf. pp. 267ff.), but he was surely not in the tradition of Aristotelian physicalism. The two philosophies are quite different, since the latter puts greater emphasis on physical energy, force, or form, rather than mere substance, and thus only physicalism properly connects science to emotional spirituality. So, in my view, materialism is a greatly truncated and distorted version of physicalism.
 Mystics should be warned that, when some ideas of materialists (e.g., quantum physicists) are used for mystical purposes, they harbor a contradiction, for materialism and mysticism have different positions and incongruent directions.
 Some persuasive theisms in the Kantian tradition hid their atheistic views just as persuasive atheisms hide theistic views today, as seen in Lawrence Krauss, an idealist, in context with Richard Dawkins, a materialist, in this video discussion.