History of Philosophy

Philosophy of the Modern Age

Great Philosophical Systems of the Modern Era

In the 17th century, Western European philosophy was enriched by several eminent philosophers who crafted their own distinct concepts:

• René Descartes (1596-1650), the father of modern philosophy, laid the foundations for a new mode of reasoning. Though his contemporaries included Galileo and Bacon, Descartes heralded a new era. His surname in Latin is "Cartesius," and thus his school is known as Cartesianism. Descartes began his philosophy by addressing the chaos prevalent in the philosophical landscape of his time. He identified the root of the problem as the lack of a robust method in philosophy. To resolve philosophical issues, one must adopt a method akin to that of mathematics, which relies on axioms—undeniable truths. Descartes sought to find an indisputable truth for philosophy and arrived at the conclusion that one could doubt everything except the act of doubting itself. Thus, doubt became the starting point for philosophy. Doubt is a type of thinking; therefore, thinking itself is an undeniable fact. If there is thinking, there must be a thinker. This truth was encapsulated in Descartes' famous dictum, "Cogito ergo sum" ("I think, therefore I am"), through which he argued for the existence of the self.
• The second question that intrigued Descartes was the existence of God. He reiterated the ontological argument for God's existence proposed by Anselm of Canterbury. Every person possesses the idea of God within their mind, despite this idea not being derived from experience. God himself instilled this idea in humans; hence, God exists.
• Not only does God exist, but He is also good and perfect. As such, He does not deceive people but grants them the possibility of true knowledge. If a person can truly know and perceives the world as existing, it follows that the world does indeed exist. Thus, Descartes, who initially doubted everything, including the existence of the world, concluded that this doubt is resolved by the existence of God.
• Descartes demonstrated the existence of three fundamental entities: God, the human soul, and bodies. God's attribute is infinity, as He is unrestricted by anything. The soul's attribute is consciousness, and the body's attribute is extension.
• Body and soul are united only in humans. Descartes then faced the question of how body and soul interact within a person. He proposed that the body does not govern the soul, nor does the soul govern the body, as they are different substances. However, the body can influence the soul's movements (e.g., pain causing sadness), and the soul can influence the body's movements (e.g., desire prompting action). Descartes' answer did not satisfy everyone, and the mind-body problem remains one of the most significant philosophical issues.
• According to Descartes, reason is a reliable source of knowledge, containing ideas of three types: innate, acquired through experience, and those constructed by the mind from the first two. Innate ideas are the most reliable, as they are implanted by God, who never deceives humans.
• In contrast to Cartesianism, Blaise Pascal (1623-1662), a French philosopher and mystic, established an opposing philosophical system. While Descartes was a rationalist, Pascal was a mystic. He believed that mathematical methods are insufficient for grasping the most crucial aspects of existence—happiness and the salvation of the soul. Pascal posited that the heart is the true source of knowledge about these important matters. A central issue for Pascal was the existence of God. Rejecting Cartesian rationalism, he could not construct a rational argument for God's existence. Instead, Pascal proposed a new form of argument known as "Pascal's Wager": if a person believes in God and God exists, they gain everything and eternity; if they believe and God does not exist, they gain nothing and lose nothing; if they do not believe and God does not exist, they lose nothing; but if they do not believe and God exists, they lose everything and eternity. Therefore, it is wiser to believe in God under any circumstances. Pascal established a strict hierarchy of values, with God being the highest and material goods the lowest. No accumulation of lower-level values can produce a higher-level value. Thus, a person who directs all their efforts toward God acts both rationally and morally.
• Another religious philosophical system was proposed by Nicolas Malebranche (1638-1715), a French philosopher who attempted to resolve the mind-body problem posed by Descartes. According to Malebranche, neither the body can act on the soul nor the soul on the body. The sequence of their actions occurs solely because God acts upon the body and the soul in such a manner. Bodies cannot act upon other bodies, nor can souls act upon other souls. The sequence of their actions is also ensured by God. There are no causal connections between things and phenomena. The world is not a unity but merely a collection of separate facts that God integrates into a single system. If Descartes attributed consciousness to the soul and extension to the body, then the soul cannot know the body. So where does knowledge come from? Pascal believed that the foundation of knowledge is God, who reveals knowledge of the body to the soul. Thus, any knowledge is, in reality, knowledge of God, who imparts ideas to the human mind. Ideas of bodies are clearer and more distinct than ideas of the soul and God.
• Thomas Hobbes (1588-1679), an English philosopher, authored Elements of Philosophy, which comprises three volumes: On the Body (1655), On Man (1658), and On the State (1642), as well as the political treatise Leviathan (1651).

✵ Hobbes addressed the Cartesian mind-body problem by eliminating dualism, arguing that spiritual substances do not exist; instead, there are only material atoms. Bodies are not independent substances but constructions of atoms.

✵ Hobbes' materialism influenced his theory of knowledge. If only material substances exist, then sensory perception is the sole means of knowledge. All human knowledge is acquired through the senses. This position is known as sensationalism.

✵ Hobbes' philosophy is notably centered on politics, which he constructed following the same model as his metaphysics. Just as the world consists of individual atoms, society comprises individual social atoms—people who are egoistic and concerned solely with their own interests. In the past, people were engaged in a constant struggle for survival, as each person, due to their egoism, was a potential enemy. Hobbes famously described this as "homo homini lupus" (man is a wolf to man). This was a state of war of all against all. To avoid self-destruction, people agreed to refrain from harming one another and to elect one among themselves (a monarch) to enforce this agreement. This doctrine is known as the theory of the social contract. Thus, Hobbes rejected Aristotle's belief that humans are inherently good and unite to fulfill their good potentials. For Hobbes, the origin of the state lies in the need to curb humanity's wicked and selfish traits.

• Benedict Spinoza (1632-1677), a Dutch Jew, articulated his views in numerous works, the most significant of which was the Theological-Political Treatise (1670). Spinoza proposed his solution to the mind-body problem. He asserted that there is only one substance (monad), which is neither spiritual nor material but has two modes of expression: mind and matter. This monad is God. Since there is nothing besides God, and everything is merely a part of God, the entire world is God. The doctrine that everything is God is known as pantheism. As everything is God, the world functions as a single mechanism, and all that exists are merely parts of this mechanism. Parts have no freedom. Therefore, Spinoza believed that freedom does not exist; it is merely an illusion. Humans cannot change their circumstances; they can only continually resist them and be unhappy, or accept inevitability, reconcile with it, and find happiness as a part of the monad. Thus, Spinoza posited that freedom is the awareness of necessity.
• The first president of the German Academy of Sciences, Gottfried Wilhelm Leibniz (1646-1716), was the preeminent German intellectual of the 17th century.

✵ He believed in the existence of many substances, all of which are immaterial. Leibniz referred to these as monads but understood the term differently from Spinoza, akin to Bruno's concept of the smallest units of existence. All substances are distinct and variable, which accounts for the diversity of things. Each substance has consciousness, but the activity of this consciousness depends on its ontological level: God's consciousness is the most lucid, while the consciousness of things is as if asleep. Since monads are immaterial, and nothing exists besides monads, Leibniz explained materiality only as an expression of monads. This interpretation allowed Leibniz to assert that freedom is a fundamental characteristic of all that exists.

✵ Leibniz made a substantial contribution to the development of logic. He was the first to propose the integration of logic and mathematics, paving the way for the development of mathematical logic. He also posited that only truths based on the principle of identity are undeniable. All other truths are derivative. They are classified into derivative truths of reason (deduced by reason from primary truths) and derivative truths of fact (deduced from observation). Both types of derivative truths must be convincingly justified. Thus, alongside Aristotle's three laws, Leibniz introduced one of the fundamental laws of logic—the law of sufficient reason.