In his Ethics, Spinoza argues that substance is that which is independent of all contingent properties or accidental attributes. As something that neither comes into being nor passes out of existence, substance is something that necessarily is, and must be independent of necessity.
According to Spinoza’s account of substance, “thought” and “extension” are two fundamental properties, or qualities of substance. Spinoza extends his account of the nature of substance to the question of the nature of God, inquiring as to whether God, as an incorporeal entity, can create material things. According to the division of substances into two types, thought and extension, Spinoza maintains that no two substances can possess the same nature or attribute, or they would necessarily be the same thing. Nor, Spinoza adds, can one substance be the cause of another, for there again, the substance causing and the substance caused would be identical.
Thus, Spinoza argues that substance must be self-caused because existence, by definition, belongs to the nature of substance. The properties of being “eternal” and “infinite” also belong to the nature of substance, as the existence of substance is contingent upon nothing other than itself. If substance were finite, then it must be caused; but this is not the case, so substance must be a single infinite thing. According to Spinoza, the more reality a thing has, the more attributes it has; hence, substance, being a single thing, must possess all infinite attributes.
If it is granted that substance is simple, eternal, and infinite, then it follows that there is no other substance but God. As the only substance, God possesses all attributes infinitely and eternally. Accordingly, from the necessity of the divine nature, there must come an infinite number of attributes, expressed in an infinite number of ways. As there are only two types of substance— thought and extension— then it follows that everything that is possible is actual and necessary.
God, according to Spinoza, is the efficient cause of all things per se, or through Himself, rather than per accidens, or through secondary causes. God is free in the ultimate sense, constrained under no force external to Himself. Human beings, on the other hand, do not possess the same freedom as God, but only believe ourselves to be free agents and the executers of our actions. Because God is the only free being, human beings are necessarily determined beings. As there is no substance but God, it follows that there is no mode of the single substance that determines itself. According to the rule of sufficient reason, a thing determined by God cannot be otherwise, or it would not be possible; and a thing could not be possible if it were not otherwise.
In his Discourse, Leibniz takes issue with the fact that Spinoza denies God a moral nature. According to Spinoza, human beings are not free to choose, and are therefore not possessors of a moral nature. By the same token, God, as the determiner of all things possible, and manifestation of all things actual, is the only free being as such; but God’s freedom is not such that some choice is involved in what is actualized, since there is nothing which is not possible which is not actual.
For example, goodness, as an attribute of the nature of God, would only serve to restrict the infinite power of God, which is not possible, since there is no other substance but God, and thus no delimitation in the nature of God whatever. According to Leibniz, God is infinite and is lacking no possible perfection. However, Leibniz maintains that “Goodness” is perfection, and so to deny this attribute to God’s nature would be to somehow place a limitation on God’s perfection. Things are not good because God loves them, but because they are good in themselves, and thus perfect in terms of God’s infinite creative power. It is necessary for Leibniz to show that the world that exists is the best of all possible worlds— or that the world that exists lacks no possible perfections.
Like Spinoza’s God, which is pure intellect, Leibniz maintains that the best possible world is created of intellects, or finite substances (monads). As a purely intellectual being, God cannot create anything but intellects; hence, the creation, under Leibniz’s system, of an infinity of minds begets an infinity of perspectives. “Minds,” according to Leibniz, means anything constituted with the faculty of perception, and everything that God creates, perceives. The physical world is therefore a vast perceiver of sorts that is harmonized together in its respective perceptions. Discord of perceptions amongst what God creates would not be in accordance with his infinite perfection, and thus all harmonized perceptions beget in turn the observable uniformity in the laws of nature.
Because God, using the fewest number of principles, creates the infinite of perspectives in nature, and the world that God creates is the best of all possible worlds, monads, being substances, never come or go out of existence, and are each unto themselves like a complete world. Like an infinity of mirrors of God, each monad reflects the entire universe from its particular perspective. As we observed, God has made the best of all possible worlds, and accordingly, God wills the most good possible. Leibniz overturns Spinoza’s amoral universe by noticing that any being possessed of a rational intellectual nature must, like God, have a free nature, and this means that every creature with a rational intellectual must be a freely choosing moral being.
It is logically impossible to bring about the greatest good without freely choosing moral beings, and thus Leibniz introduces his conception of theodicy to account for the existence of evil in the world. If every event and action were determined by God, anything He creates, whether possessed of an intellectual nature or not, would be a kind of puppet rather than a free agent. Because God, in order to bring about the maximal good in the best of all possible worlds, creates beings that are free moral agents, absolves Himself of responsibility for the evil that exists in the world. Leibniz notes, however, that even what appears to be evil is actually, in the end, turned to good, and is thus an evil necessary to bring about the maximal good in the created world.