I believe that the Renaissance philosopher who has provided the greatest contribution to humanity is Rene Descartes, whose aggregate contributions to intellectualism in Western culture are difficult to overstate. His significance lies in his judicious use of skepticism in the assessment of truths and beliefs frequently held up as objective knowledge. Descartes was a Catholic, but this did not necessarily mean that he took its authoritative and hegemonic role in the maintenance of knowledge at face value.
He realized that certain truths cannot be satisfactorily determined through Church teachings alone, and therefore what must be held up to close scrutiny is not ‘truth’ itself but the criteria used to assess it. Granted, Descartes was not the first person to examine such issues. The skeptical tradition dates as far back as the first millennium AD. But rather than asserting that truth has no value, Descartes was concerned with the development of a unified and almost arithmetic means of measuring knowledge.
This sense of skepticism blended with a belief in ordered reasoning is reflected in his other pursuits, particularly mathematics. This combination of mathematics and sophistry is made most manifest in Cartesian dualism, which argues a divide between the nonmaterial mind/soul and the material of the body that influences each other. However, it is Descartes’ ordering of metaphysics that has provoked the most significant amount of reaction and influence in equal measures supporting or contradicting him.
Descartes believed that in order to prove the existence of the material world, one must first prove the existence of the self, which he posited as self-evident because “Cogito ergo sum” or “I think, therefore I am. ” The reaction to these assertions is primarily split along two lines: skepticism and idealism. George Berkeley’s disagreement falls in the latter category, as he opined that Cartesian dualism implied that we cannot know anything beyond the sensations and ideas our mind believes to exist, while David Hume problematized why we believe in the existence of an external in the first place.
John Locke developed a more nuanced understanding of the mind-self by defining it as a “conscious thinking thing” whose materiality or immateriality is irrelevant to acknowledging that it is conscious of sensation and emotion. Locke also posited that the body is also crucial to the formation of the mind-self, arguing that the mind-self is a tabula rasa, a blank slate shaped by experience, including natal sources of experience. Immanuel Kant developed an elaborate set of transcendental arguments and categories as a means f proving the existence of external reality.
Essentially speaking, while sensations and perceptions do exist, they are meaningless without a unified comprehension of them. As such, experience is formed by the mind-self being able to cohere these impressions together as something meaningful. George Hegel challenged the understanding of truth as not just a concern with matters of substance, but matters of the subject perceiving and comprehending truth. As such, truth is just as contingent on the mind-self which thinks.
Thus, unlike Berkeley, external realities are not just mere mental content, but an expression of thought itself. Descartes may have found few adherents during his time and years after, but his importance to succeeding philosophers who have attempted to deconstruct the contents of the mind and its relationship and understanding of the external world. In effect, he ushered in a fundamental level of doubt in assessing truth and knowledge so necessary in abnegating the kind of dogmatism which makes unquestioned acceptance of ‘common wisdom’ so problematic.