Descartes’ influence has been profound. His criticisms of scholasticism and elevation of rational introspection were seminal for Continental Rationalism. His focus on the experience of the individual subject has had a profound influence into the present. However, there were also immediate criticisms of his views. We see this especially in reference to his proofs for God’s existence. Beyond that, over time philosophers increasingly have questioned whether it is even possible to radically doubt everything that Descartes claims to doubt, whether his introspective rationalism can lead to sufficient understanding of the world, whether his view of the self is at all satisfactory, and whether we can have or need absolute certainty. Indeed, if one thing separates contemporary epistemology from Descartes it is that we have largely given up on the early modern search for apodictic certainty.
Criticisms of Descartes’ Ontological Proof
Most philosophers today think that Descarte’s ontological arguments are troubling. For any argument to be true, not only must the argument be valid, but the premises must also be true. The version provided formally in the last section immediately drew charges for having incorrect premises. Do we really all have the idea of a most perfect imaginable being? Anthropology tells a different story, namely that most early societies had views of deities that had different powers but no view of an all-powerful, perfect deity. Think of the Greeks or many Native American religions, for example. Further, Kant and others have questioned whether existence is a quality of things at all, thus whether it is a perfection. The second argument provided — that God must have implanted the idea of himself, as innate to human consciousness — also immediately drew its critics. Is the idea of a perfect being more perfect than a being that imagines such an idea? The long and short of it is that Descartes’ and other versions of the ontological proof have met with anything but universal acceptance within the field of philosophy. Details of various versions of the ontological argument and criticisms of them can be found here.
Solipsism
In light of the criticism of Descartes’ proof for God’s existence, some people have maintained that, if we honestly assess Descartes’ arguments, Descartes ends up with a position known as solipsism. A solipsist believes that only he exists and that everything else is a figment of his or her imagination. If only Descartes’ proof for his own existence works logically and no further proofs are absolutely convincing, then solipsism is a real possibility. However, even if one only knew that one existed, it would not follow that one should rationally act on the basis that this in fact is the only truth. One might rationally conclude that our ability to know facts with certainty is not great; so we will be best served by adopting views that are most probable. This indeed is the view of most contemporary philosophers. Such a view would lead us to reject solipsism in short order, as it is an extraordinarily mad perspective that will not work well in our daily lives.
General criticisms of the Method of Systemic Doubt
There are numerous criticisms of Descartes’ systemic doubt. A strong one concerns whether we would be able to offer any criticism at all if we truly engaged in such questioning. To systemically engage in systemic doubt, wouldn’t we have to doubt the meanings to the words we use? Wouldn’t we have to doubt the possibility of logic to construct a worldview that we should believe in? Had Descartes actually succeeded in systemic doubt, he would have had to remain silent.
Descartes’ own reconstruction of a worldview is done without a clear justification of reason. But any justification of reason would in any case be circular. Blaise Pascal, previous to Descartes, had already pointed that any rational justification of reason must presuppose first principles of reasoning. Goedel’s Incompleteness Theorems in logic make a similar point in the 20th Century. Any argument for the validity of reasoning will presuppose the tools that it is using in the argument. A faith in reason seems to be required.
Hermeneutic philosophers in the late 20th century in particular highlighted how we always must begin our thinking with some of the presuppositions of the tradition from which we come. But even Aristotle had already pointed to first principles that must be used, though he claimed they could be intuited as true. One thing is certain: Despite Descartes innovations, his views have the marks of the history of philosophy all over them. His argument that we have certain existence of the self is already mentioned by St. Augustine in the 4th century CE. His view of the soul as a thinking substance seems to owe much to Avicenna’s 10th century CE  floating man (or flying man) argument. The ontological argument that he offers was first offered by St. Anselm of Canterbury in the 1oth century. His atomism is inspired by Democritus, the Ancient Greek philosopher.
Descartes’ Dualism
Descartes’ dualism is criticized on many counts. One of the major types of criticism highlights that, writing before Darwin’s influence, Descartes radically over-estimates the differences between human consciousness and the consciousness of other animals. More generally, he doesn’t understand the material basis of animal and human cognition. These criticisms go in multiple directions.
Another line of attack comes from environmental philosophers, who see in Descartes’ mechanical philosophy the roots of a more general administrative or technological approach to the natural and human world that is the root of our environmental crisis. It has lead to an engineering spirit that while opening many possibilities for human beings is ultimately undercutting the viability of the natural world that we depend on. Calls for an organic worldview to oppose the Cartesian and early enlightenment mechanical one go back to Hegel and the Romantics, but have been given new vitality by environmental thinkers such as Carolyn Merchant. In such a worldview we are to understand the self as fundamentally interlinked with and dependent on the physical and social contexts of which it is a part.
