Philosophy of the Modern Era and Enlightenment

Rationalism of René Descartes and Baruch Spinoza

European rationalism flourished in the works of the French thinker René Descartes (1596—1650), a member of the "noble mantle" class who also made significant contributions as a physicist and mathematician. Descartes is rightfully considered the founder of geometric optics and the creator of analytical geometry, with his Cartesian coordinate system being a notable legacy. His ideas also laid the groundwork for modern psychology, particularly the concept of conditioned reflexes.

In his quest for a reliable method of knowledge, Descartes adopted a path of doubt, deciding to doubt everything that could be doubted. For Descartes, doubt symbolizes an "absolute beginning." He believed that a person could doubt everything—from their own senses to the existence of the external world, encapsulated in the phrase "De omnibus dubitandum est" (Everything must be doubted). However, one thing a person cannot doubt is the act of doubting itself. Doubt proves the existence of thought, and thus, the existence of the thinker, which he famously summarized as "Cogito ergo sum" (I think, therefore I am). This reasoning is known as Descartes' motto and the process by which it is reached is termed "Cartesian doubt."

Descarte's assertion aims to provide a solid foundation for knowledge by rejecting any superstitions that may masquerade as truth and starting from the most fundamental aspect of thought to achieve genuine understanding of the world. This approach is closely tied to the development of mathematics, which is based on ideal constructions (axioms). In this framework, Descartes’ thinking "I" requires nothing beyond itself for its existence, being a spiritual substance (res cogitans) that is not dependent on material things.

Descarte sought the objective measure of truth not in the external world or practical activity but within the inherent qualities of the mind itself. For him, clarity and distinctness were the highest criteria of truth. Consequently, Descartes endorsed the notion of "innate" ideas and thus recognized their divine origin. His ontological argument for the existence of God includes the following: God is the most perfect being; perfection includes existence, thus God exists. Another argument is that my own existence can only be explained by the existence of God, for if I appeared by myself, I would have endowed myself with the highest virtues. If I come from others (parents, ancestors, etc.), then there must be a first cause, which is God.

Descartes' work "Discourse on the Method," written in French rather than Latin, significantly contributed to scientific analysis. In this work, Descartes formulates the fundamental rules of scientific inquiry, which include:

1. Never accept anything as true until it is clearly recognized as such.
2. Divide each problem into as many parts as necessary for its adequate resolution.
3. Present ideas in proper sequence, starting from the simplest and most evident.

These principles were crucial for the development of science and philosophy during the Enlightenment. The conditions of "evidence" and "intuitive clarity" for fundamental statements in scientific theories are still considered essential characteristics of scientific knowledge today, given that Descartes' main method for acquiring true facts was rational deduction.

The Dutch thinker Baruch Spinoza (1632—1677) was deeply influenced by Descartes and sought to build his philosophy on unquestionably certain foundational propositions. He found a model of such certainty and rigorous proof in geometry with its axioms and clear deduction of theorems. In his work "Ethics," Spinoza presents the following axioms:

1. Everything that exists exists either in itself or in something else.
2. What cannot be conceived through another must be conceived through itself.
3. From a given cause, an effect necessarily follows, and vice versa—without a specific cause, no effect can occur.
4. Knowledge of the effect is directly dependent on knowledge of the cause and contains it.
5. Things that have no relation to one another cannot be understood through each other.

Spinoza held that there is only one substance—nature—which is self-caused (causa sui) and thus does not require anything or anyone else for its existence. According to Spinoza, nature is both the active nature (natura naturans) and the created nature (natura naturata). His doctrine of substance, known as pantheism, posits that nature is eternal and infinite, encompassing both cause and effect, essence and existence. Nature as an active principle is equated with God, who is immanent and exists independently of human thought. Spinoza contended that the infinite mind could comprehend this nature, though human understanding can grasp only two attributes of substance: extension and thought.

Spinoza also ventured into religious matters, attempting to reconcile biblical texts with philosophical analysis, thus initiating a critical method for studying the Bible. He wrote that a proper method of interpretation should avoid proving pre-existing beliefs and instead focus on understanding the text's inherent meaning. According to Spinoza, the nature and existence of God are understood not through miracles but through immutable and undeniable natural laws, clear and self-evident ideas. While his predecessor, the Jewish thinker Maimonides (1135—1204), believed that faith should be supported by rational argument but retained a supernatural element in his worldview, Spinoza's system does not accommodate such supernatural aspects. For Spinoza, everything occurs according to natural laws and within the framework of reality, rejecting the notion of transcendence or a final purpose of creation. Critics like Lev Shestov argued that Spinoza and similar philosophers did not truly grasp the concept of God, suggesting that what they referred to as God was not God at all.

Modern scholars consider that the period of the Enlightenment established the understanding of rationality that continues to be significant today. The type of rationality from the 17th century cannot be reconstructed without considering both natural science and metaphysics of that time, as only their integration reveals the profound new horizons of thought.