Elementary features of Cartesian rationalism (part I)

Cartesian philosophy marks a turning point in the history of Western thought. Contrary to an assumption shared by most Renaissance thinkers, Descartes did not begin with a spontaneous and uncritical credulity about the workings of nature, nor did he display the same reverence for classical philosophy as his contemporaries. Motivated by the ongoing Scientific Revolution and the need to refute radical skepticism, his main goal was to create a philosophical system capable of anchoring recent advances in physics.

Descartes then sought to establish a method that would allow him to objectively distinguish between what is false and what is true. It should be noted that certain methodological nuances originating from medieval philosophy still persisted at the time he completed his academic training. Having studied for six years at the Jesuit college in La Flèche, where a predominantly scholastic teaching paradigm prevailed, the French philosopher would later demonstrate his dissatisfaction with the model of disputationes. His conviction was unshakable that anything uncertain is incongruent with science, as it lacks a method that allows for the perception of the occurrence of errors.

It is important to remember that Scholasticism developed in close connection with Aristotelianism, inheriting, among many other aspects, its physics. Aristotelian physics considered a qualitative notion of being, designating "substantial form" as the internal principle from which a body's action, that is, its movement, springs. In turn, in the Cartesian system, the cosmos is interpreted as a kind of algorithmic extension, so that all phenomena can be explained mathematically. This means that Descartes dispenses with the qualitative attribute of being, asserting that nature is measurable and that, in this sense, the physical world is essentially quantitative.

From an epistemological perspective, the French philosopher distances himself from the Aristotelian-Thomistic tradition—whose cornerstone was the inquiry into the existence of the object in question—advocating a new spectrum of analysis that concerns not only the relationship between thought and its sensible correlates, but above all the characteristics of the noetic act itself, which transcends any possible correspondence with the corporeality of the world. Thought cannot always identify an external reality that suits it, making it important to interrogate its connection with the world.

It was mathematics that revealed the relevance of this question to Descartes, since mathematical knowledge validates the assertion that there are concepts that, despite lacking a sensible correlate, nevertheless contain a reality of their own that can be understood by the human intellect. Cartesian rationalism challenges this science not only as objectively precise when applied to the world, but also as a possibility of freeing reason from qualitative elements generated by the appreciation of empirical data. Descartes intended to show, therefore, that the intellect is capable of knowing on its own, that is, without the need to resort to any sensory-perceptual content. The process by which human beings know things, that is, the set of cognitive functions that leads to the acquisition of knowledge, then becomes the primordial axis of philosophical thought; this epistemological redirection would ultimately assume pivotal importance in the development of Western culture, which is why the French mathematician is credited with founding modern philosophy.

Cartesian doubt does not arise from the experience of systematic error, but rather from the need to separate truth from falsehood; it is a voluntary, methodical, and, later, hyperbolic doubt. Epistemologically, it is imperative that everything that might give rise to ambiguity be questioned, unlike what happens in everyday reality, where humans guide their practice based on what is plausible. In the second part of the Discourse on the Method , drawing on a logical procedure used by geometers, Descartes presents the four precepts that, in his view, are indispensable for ensuring the epistemic validity of knowledge:

The first consisted of never accepting anything as true without clearly knowing it as such: (…) of including in our judgments only that which presented itself so clearly and distinctly to my mind that I had no occasion to doubt it. The second was to divide each of the difficulties I was to examine into as many parts as possible and necessary to best resolve them. The third was to conduct my thoughts in order, beginning with the simplest and easiest-to-understand objects, gradually ascending (…) to the knowledge of the more complex. And the last was to always make enumerations so complete and reviews so general that I was certain of omitting nothing.

It seems reasonable to us that Cartesian doubt lacks, in the Discourse on Method , the metaphysical dimension that is discernible in other texts. Indeed, in the preamble to the fourth part of this work, the French philosopher highlights three factors that justify the application of methodical doubt: 1) we know that information derived from the senses is misleading, so no empirical belief should be taken as true (this argument is corroborated by skeptics and calls into question the validity of a posteriori knowledge). 2) in the realm of logic and mathematics, human beings commit paralogisms in the simplest reasoning. 3) certain dreams are indistinguishable from our waking perceptions, and as such, there is no certainty that life itself is not a dream.

However, in the Meditations on First Philosophy , with the evocation of the deceptor argument (a deceiving god), doubt reaches its hyperbolic phase, with the suspension of judgment applying to all reality extrinsic to thought; this moment translates, therefore, into the total suspension of the world's ontology. However, even considering the hypothesis of a god who could constantly deceive him about everything, Descartes intuits with great clarity and distinctness its existence as a "thinking thing." Ultimately, doubt applies to everything except itself; that is, in epistemological terms, it is possible to doubt any and all thinkable content; however, it is not possible to doubt the formal reality of doubt itself. This is because doubt represents a unity of thought, and thought in action is already a form of being whose reality cannot be questioned: I think, therefore I am (cogito, ergo sum). This is, in effect, the foundational principle that supports the validity of knowledge and that consequently allows us to refute radical skepticism.