Philosophy of the Modern Era

The Doctrine of Substance

The problem of substance is approached differently in the philosophy of the New Time compared to ancient and medieval philosophies. This issue finds elaboration primarily within the philosophical systems of Descartes, Spinoza, and Leibniz. Here, substance is understood as that which "exists in itself and is represented through itself; that is, its representation does not require the representation of another thing from which it must be formed." This understanding contrasts with Aristotle's conception, which viewed substance as individual entities, such as green trees or rectangular tables, in opposition to their properties of "green" and "rectangular." It also differs from the medieval understanding, which clearly distinguishes between the being of God and the being of the world, examining the problem of substance through this divergence. In the philosophical systems of Descartes, Spinoza, and Leibniz, while God plays an exceptionally important role, the issue of substance shifts towards the consideration of nature. Descartes posits the existence of two substances: the corporeal and the thinking. "Extension in length, width, and depth is the nature of corporeal substance, while thinking is the nature of the thinking substance," writes Descartes. Furthermore, he asserts that the term "substance" ambiguously applies to both God and His creations, for "the only substance that needs nothing else can only be God. The possibility of the existence of all other substances can be grasped only with the help of God."

A different understanding of substance is found in Spinoza, who devotes significant attention to this problem in his "Ethics." Spinoza argues that two substances cannot exist; there can only be one, as it contains the entirety of being, eternal in time and unbounded in space. Nothing can exist alongside this substance. He refutes Descartes' duality in both senses, asserting that God and nature are one and the same. God did not create nature; it is eternal. Spinoza consistently develops a pantheistic position, identifying nature with God, for which he faced persecution from both Jewish and Christian churches. He also rejects Descartes' division of substance into corporeal and thinking, claiming that extension and thought are not two substances but attributes (an attribute being an inseparable property of the substance) of a single substance. Substance, in general, has an infinite number of attributes, which we can never fully comprehend (otherwise we would define God), but knowing the two mentioned attributes is sufficient for us to understand and judge the substance, even if our knowledge remains limited. Substance is directly given to us in the form of modes, that is, specific things and mental processes. A mode is that which "exists in another and is represented through that other."

A characteristic feature of Spinoza's understanding of substance is its conception as constant and unchanging. Movement is merely a mode of substance, not its attribute. Furthermore, Spinoza understands movement solely as mechanical motion. In the world, necessity operates, and randomness is absent. "In the nature of things, nothing is contingent; everything is determined to exist and acts in a known way through the necessity of divine nature."

Leibniz, in his polemics against Spinoza and other philosophers, develops his own understanding of substance. He refers to substances as monads—"the true atoms of nature," "the elements of things." Monads are the simplest, indivisible metaphysical particles. They are metaphysical because they possess no length and are not located in space. They are centers of active force, spiritual substances that continually change, do not arise or perish through natural means, are unique, and do not influence one another. Monads are created by God, and their harmony is also established by Him; hence, there exists a correlation between mental and physical states. Monads possess varying degrees of consciousness, resulting in a hierarchy of monads. There are simple, or bare, monads with only vague perceptions underlying inorganic nature; soul-monads that possess sensations and ideas; and spirit-monads, which form the basis of rational beings. The main difference between Leibniz's understanding of substance and Spinoza's lies in two aspects: for Leibniz, substance is multiple, whereas for Spinoza it is singular; for Leibniz, substance is active, capable of self-transformation and development, while for Spinoza, it is passive, capable only of mechanical motion.