In seventeenth-century Europe, the question of the basis of certain knowledge intensified amid science and mathematics, crusades and political changes, and the transformation of the institutions of knowledge. Descartes, Spinoza and Leibniz are often referred to as the intellectuals. This classification is useful for study, but the ideas of the three philosophers are not identical. 28.1 The methodological doubts of Descartes Descartes seeks a faith that can withstand the severest test of doubt. The senses are confused. dream experiences can explain the waking experience. so they gradually doubt their beliefs. But one thing that cannot be denied when doubting is the contemplative existence of the doubter. This is where the famous conclusion of the cogito comes in. The purpose of this doubt is to find a definite basis, not a permanent doubt. Parallel philosophy accepts Descartes ' skepticism as a disciplined method, but does not regard universal skepticism as the norm of everyday knowledge. The Nyaya tradition examines the specific causes of suspicion, while Descartes systematically raises broader doubts. Comparison is useful and should not be confused with equality. 28.2 The Duality of the Mind Descartes distinguishes between the mind as the deliberative element and the body as the expansive element. This division leads to new questions of consciousness, identity and the body. But then the difficulty arises as to how these different elements form a causal relationship with each other. Many of the questions of modern philosophy of mind are connected to this Cartesian heritage. 28.3 Spinoza: One element is a number of properties Spinoza replaces the dualism of Descartes with a monism. Ishvara or Prakriti is understood to be two names for the same infinite essence. Mind and body are not two independent entities but different qualitative expressions of the same reality. In the philosophy of Spinoza, freedom is not an arbitrary will. I am part of the cause-order. Real freedom lies in understanding needs, breaking free from emotional bondage and developing intellectual life. In this view, ethics links back to a cosmological understanding. 28.4 Emotions and freedom The importance of ethics lies not only in metaphysics; Spinoza understands fear, hope, jealousy, love, hatred and desire causally. Rather than dismissing emotions as mere moral quandaries, one must understand their origins. A direct analogy with modern psychology is not appropriate, but the causal analysis of emotional life is philosophically remarkable. 28.5 Leibnitz: Reason enough Leibniz asks why there is a zero. According to the doctrine of sufficient reason, a fact or truth must have a just cause. Simultaneously, he develops the theory of contradiction, the concept of possible worlds, monads, and preconceived notions of harmony. The concept of the possible world has a broad influence in modern modal philosophy, although modern usage may differ from Leibniz 's original metaphysics. 28.6 The Monad and the Multitude Leibniz 's monads are simple, indivisible elements that reflect the world in their own way. Different perspectives can give different presentations of the same world. Parallel philosophy may here take metaphysical inspiration from polytheism, but does not declare its theories to be the direct historical successors of Leibniz. 28.7 The Limits of Rationalism Descartes, Spinoza, and Leibniz all held high ideals of mathematical clarity and logic and theory. But without sufficient connection to experience, reason can cut off the self from the world. For this reason, later empiricist traditions question where the content of thought comes from. Caution of the 28.8 Classification The textual division of the intellectual versus empiricist text is an early map of philosophical history, not the terrain itself. Descartes talks about experience. using Locke 's logic. Leibniz does not deny experience. Parallel philosophy studies each thinker in the complexity of their reasoning. Pūrvapakṣa (Prima Facie View): The pursuit of a certain knowledge is an impossible ideal Uttarapakṣa (Response): Absolute infallibility is not possible, but clarity and the ideal of cross-examination are valuable. The problem lies in making infallibility a necessary condition of knowledge. Parallel philosophy tends to favor error correction knowledge. 28.9 Limitation of reasonable doubt Descartes 's skepticism is a method of finding a definitive basis for not permanently abandoning all belief systems in life. The senses sometimes give off illusions; dream experiences seem to awaken - and systematic deception in thought may be considered possible. But nothing is certain: the findings themselves are an act of skepticism. The power of this method lies in removing unfounded beliefs; the limitation is that everyday knowledge does not demand infinite certainty. The court relies on scientific and civil probabilities, corroborative sources, and error-checking. Not all claims are created equal due to the lack of absolute certainty. 28.10 The Interaction of the Mind-Body If the mind is a thinking substance without expansion and the body is an expanding substance, how do the two affect each other? The desire causes the hands to rise, and the hurt causes pain. Descartesian dualism preserves the distinction between the individual consciousness of experience and the physical body, but makes interaction difficult. Modern consciousness-philosophy has a new form of this problem; however, to say that Descartes is directly opposed to modern neurology is incorrect. Historical theory should be understood within the context of the mechanical nature of its time. Parallel studies do not devalue personal experience and require public scrutiny of physical evidence. 28.11 The Monotheism of Spinoza Spinoza considers God or nature as the only infinite substance. mind and body are not independent substances but are understood as different qualitative expressions of one reality. Here, God is not the cause of craftsmen outside the world. This leads to tension with traditional individualistic theosophies. Monothelitism is similar to Advaita in that quick conclusions are often wrong. The ideological background of intellectual love is different, as are Brahman, Maya, the quality of the self, moksha, and Spinoza 's quality of matter. The comparison must be to a question of dependence, unity and difference, not semantic indivisibility. 28.12 Necessity and Freedom and Emotion According to Spinoza, man often considers his will to be free because he does not know the cause of the will. Freedom does not mean an irrational choice; it means an adequate sense of necessity and an increase in active emotion. Knowledge of the emotions that make a person inactive under external factors can make a person more active. This view encourages understanding by minimizing moral culpability, but eliminating accountability would make justice harder. Parallel philosophy combines causal understanding, prevention and improvement, and the defense of dignity. Social responsibility is concerned with the person being part of a chain of causation. 28.13 A sufficient reason for Leibnitz to The theory of sufficient reason asks why this is so and why not otherwise. Just counting events is not an explanation. Leibniz tries to understand the existence and order of the world through the distinction between truths necessary for a possible world and factual truths. But asking for sufficient reason for everything begs the question of how the ultimate reason itself can be supported and whether human knowledge can reach that reason. Theory is a useful question in applied research, not a claim to have found a complete explanation. The search may continue as uncertainty is accepted. Chapter Conclusion From Descartes ' discipline of skepticism to Spinoza 's unity of reality and causal understanding, Leibniz brings out the seriousness of sufficient reason and probability. All three together form the major questions of modern European metaphysics and epistemology, but it is not appropriate to confine them to a single intellectual room. Chapter Bibliography René Descartes — Meditations on First Philosophy; Discourse on Method. Baruch Spinoza — Ethics; Theological-Political Treatise. G. W. Leibniz — Monadology; Discourse on Metaphysics; New Essays on Human Understanding. Margaret Wilson — Descartes. Michael Della Rocca — Spinoza. Robert Merrihew Adams — Leibniz: Determinist, Theist, Idealist.