In addition to founding modern philosophy, Descartes initiated one of the competing schools within it. The cartesian school is known as ‘rationalist’ and has a preference for a priori knowledge over a posteriori knowledge, i.e., it privileges knowledge which is not empirical over knowledge gained from sense-data, and privileges theoretical deduction over knowledge gained through the use of the five sense.
Descartes hoped to build a reliable foundation for knowledge on those three things which he thought to be most certain: the truths of geometry and algebra, the confidence that any rational agent has about her or his own existence, and existence of a non-contingent being on whom other contingencies rest.
Given the centrality of arithmetic and mathematical truths in cartesian thought, it became obvious for students to ask about the nature of such truths. In this question, modern philosophy inherited some questions which had been discussed in both medieval and ancient philosophy. This topic is often labelled as the “problem of universals.”
This debate, according to Tad Schmaltz, “concerns the ontological status of universal features of reality.” For example, the system of Euclidean geometry yields certain results - and those results hold equally in Europe and North America, equally last year and next year. They are universal.
An interpretive question asks how, exactly, Descartes regarded what he viewed as, in Schmaltz’s words, “eternal truths.”
The ancient antecedents of this debate see one side in Plato, who considered such eternal truths to be not physical but rather metaphysical objects and considered them to exist both outside the physical natural world and outside the human mind. They see the other side in Aristotle, who located these truths in the natural physical world.
The medievals were bequeathed this dispute, and refined the argumentation on both sides with increased nuance.
Plato should not, however, be seen as an early version of Descartes; nor should Aristotle be seen as an early version of John Locke.
While Plato and Descartes may have shared a fondness for a realism about abstractions, they were quite different in other ways.
The interpretive questions for those who study Descartes include these: what did he consider to be in the category of metaphysical objects? What, according to him, are those things which we can consider to be outside the realm of physical objects? Which realities are not detectable by the five senses?
Two competing views of him emerge: one view sees him as minimally metaphysical and as assigning relatively few objects to the category of metaphysical object; the other view sees him as richly metaphysical, populating the metaphysical realm with many objects and with many different types of object.
Tad Schmaltz describes the interpretive schism:
The division in the recent literature on Descartes is between those who see him as adopting the broadly Platonic view that immutable natures are independent both of the human mind and of the particular objects in the created world that exemplify those natures, on the one hand, and those who see him as endorsing a conceptualist reduction of such natures to features of the human mind, on the other.
A closely related question is this: is our idea of a truth identical with the truth itself?
As Schmaltz writes, there is textual evidence on both sides of these questions. Descartes’s writings are ambiguous.
There is a related controversy regarding the ontological implications of Descartes’s famous (some would say infamous) doctrine of God’s free creation of eternal truths. Though there is some support in Descartes’s texts for the identification of these truths with the ideas concerning them that God has imprinted in our mind, there also is reason to worry that such an identification cannot fully accommodate everything that Descartes has to say concerning eternal truths and immutable natures.
So, on the one hand, there is a debate about whether or not eternal truths are identified with our ideas concerning them. On the other hand there is a debate about whether immutable natures are features of the human mind or whether immutable natures are independent both of the mind and of the physical world.
These two debates are intricately linked, to the point that the question could be posed as to whether they perhaps constitute only one debate, cast in two different sets of vocabulary.
Are the words ‘eternal truths are identified with our ideas concerning them’ equivalent to the words ‘immutable natures are features of the human mind’? Again, are the words ‘immutable natures are independent both of the human mind and of particular objects in the created world’ equivalent to the words ‘eternal truths are not to be identified with our ideas concerning them’?
