Spirituality – René Descartes

Historical Impact

Emancipation from Church Doctrine

Descartes has often been dubbed the father of modern Western philosophy, the philosopher that with his skeptic approach has profoundly changed the course of Western philosophy and set the basis for modernity. The first two of his Meditations on First Philosophy, those that formulate the famous methodic doubt, represent the portion of Descartes’ writings that most influenced modern thinking. It has been argued that Descartes himself didn’t realize the extent of his revolutionary gesture. In shifting the debate from “what is true” to “of what can I be certain?,” Descartes shifted the authoritative guarantor of truth from God to humanity. (While the traditional concept of “truth” implies an external authority, “certainty” instead relies on the judgment of the individual.) In an anthropocentric revolution, the human being is now raised to the level of a subject, an agent, an emancipated being equipped with autonomous reason. This was a revolutionary step that posed the basis of modernity, the repercussions of which are still ongoing: the emancipation of humanity from Christian revelational truth and Church doctrine, a person who makes his own law and takes his own stand. In modernity, the guarantor of truth is not God anymore but human beings, each of whom is a “self-conscious shaper and guarantor” of their own reality. In that way, each person is turned into a reasoning adult, a subject, and agent, as opposed to a child obedient to God. This change in perspective was characteristic of the shift from the Christian medieval period to the modern period; that shift had been anticipated in other fields, and now Descartes was giving it a formulation in the field of philosophy.

This anthropocentric perspective, establishing human reason as autonomous, provided the basis for the Enlightenment’s emancipation from God and the Church. It also provided the basis for all subsequent anthropology. Descartes’ philosophical revolution is sometimes said to have sparked modern anthropocentrism and subjectivism.

Mathematical Legacy

One of Descartes’ most enduring legacies was his development of Cartesian or analytic geometry, which uses algebra to describe geometry. He “invented the convention of representing unknowns in equations by x, y, and z, and knowns by a, b, and c”. He also “pioneered the standard notation” that uses superscripts to show the powers or exponents; for example, the 4 used in x4 to indicate squaring of squaring. He was first to assign a fundamental place for algebra in our system of knowledge, and believed that algebra was a method to automate or mechanize reasoning, particularly about abstract, unknown quantities. European mathematicians had previously viewed geometry as a more fundamental form of mathematics, serving as the foundation of algebra. Algebraic rules were given geometric proofs by mathematicians such as Pacioli, Cardan, Tartaglia and Ferrari. Equations of degree higher than the third were regarded as unreal, because a three-dimensional form, such as a cube, occupied the largest dimension of reality. Descartes professed that the abstract quantity a2 could represent length as well as an area. This was in opposition to the teachings of mathematicians, such as Vieta, who argued that it could represent only area. Although Descartes did not pursue the subject, he preceded Leibniz in envisioning a more general science of algebra or “universal mathematics,” as a precursor to symbolic logic, that could encompass logical principles and methods symbolically, and mechanize general reasoning.

Descartes’ work provided the basis for the calculus developed by Newton and Gottfried Leibniz, who applied infinitesimal calculus to the tangent line problem, thus permitting the evolution of that branch of modern mathematics. His rule of signs is also a commonly used method to determine the number of positive and negative roots of a polynomial.

Descartes discovered an early form of the law of conservation of mechanical momentum (a measure of the motion of an object), and envisioned it as pertaining to motion in a straight line, as opposed to perfect circular motion, as Galileo had envisioned it. He outlined his views on the universe in his Principles of Philosophy.

Descartes also made contributions to the field of optics. He showed by using geometric construction and the law of refraction (also known as Descartes’ law or more commonly Snell’s law) that the angular radius of a rainbow is 42 degrees (i.e., the angle subtended at the eye by the edge of the rainbow and the ray passing from the sun through the rainbow’s centre is 42°). He also independently discovered the law of reflection, and his essay on optics was the first published mention of this law.

Influence on Newton’s Mathematics

Current opinion is that Descartes had the most influence of anyone on the young Newton, and this is arguably one of Descartes’ most important contributions. Newton continued Descartes’ work on cubic equations, which freed the subject from the fetters of the Greek and Macedonian perspectives. The most important concept was his very modern treatment of independent variables.

Contemporary Reception

Although Descartes was well known in academic circles towards the end of his life, the teaching of his works in schools was controversial. Henri de Roy (Henricus Regius, 1598-1679), Professor of Medicine at the University of Utrecht, was condemned by the Rector of the University, Gijsbert Voet (Voetius), for teaching Descartes’ physics.

Luc Paquin