Note: I discuss a few of these thoughts regarding the presuppositional method of apologetics here. In this post I will look at a 17^th century version of presuppositionalism drawn from Rene Descartes, who is often considered the father of modern philosophy.

The more I read the great authors of the western intellectual tradition, the more I realize there really is nothing new. This occurred to me once again when I was reading through the works of René Descartes and discovered that he maintained a presuppositional bent in his argumentation for God’s existence. This experience took me back to the time when I first learned the basics of philosophical theology and apologetic method. Like most who begin exploring the field of Christian apologetics, I was introduced to the presuppositional school of apologetics. Mostly, I read Greg Bahnsen, Cornelius Van Til, Gordon Clark, and John Frame. I read other authors related to the presuppositional school but I never found the method to be conceptually coherent or rationally compelling. Interestingly enough, when I went back to re-read Descartes for my doctoral work, I discovered that presuppositional apologetic thinking is not new, certainly not just a twentieth or twenty-first century phenomenon, and the same problems with the method still apply.¹ (In many ways the presuppositional school of apologetics closely corresponds to Kantian transcendental idealism and German idealism in general such as Kant, Hegel, Schelling, etc., but that is a topic for another post.) By “presuppositional method” I am referring to any apologetic approach that presupposes the truth of Christianity or the Christian God and then reasons from that point.

I especially enjoy reading the earlier thinkers who contribute to philosophy and theology because they often shed light on today’s intellectual issues and thinking in ways that might be overlooked or missed. I’ve read Descartes many times in my academic career and the presuppositional character of his work went unnoticed. Only recently did it stand out to me. That’s the great thing about reading a truly classic author. One can always learn something new.

To begin, Descartes was a rationalist. In contrast to other philosophers, who take the reality of Being as a fact and use that fact (derived from sense experience) as a point of philosophical departure, rationalists such as Descartes think that the truth about reality can be acquired by reason alone. This is an important point which explains why he thinks God must be presupposed when it comes to explaining the nature of reality.

Descartes presents a presuppositional argument for the existence of God based on the idea of God as a Perfect Being. To be fair, Descartes presents several different arguments for God’s existence in his writings. Here, I am mostly concerned with his presuppositional approach found in his Discourse on the Method of Rightly Conducting Reason, and Meditations on First Philosophy. All his arguments, however, are rational in nature (appealing to reason alone) and based on the idea of God, and establishing the existence of God based on geometrical argumentation. Descartes’s Perfect Being argument is similar to the ontological argument, a kind of proof for God’s existence: God must exist inasmuch as the attribute of existence or, in some forms, necessary existence, is part of his nature. Descartes version of the argument simply contends that a Perfect Being must exist because existence is property of perfection. Descartes attempts to demonstrate that God can be proved the same way one can rationally solve a geometrical equation, simply by following the rules of reason. While contemplating the axioms of geometry, Descartes applies the same rational mathematical reasoning to the existence of God,

For to take an example, I saw very well that if we suppose a triangle to be given, the three angles must certainly be equal to two right angles; but for all that I saw no reason to be assured that there was any such triangle in existence, while on the contrary, on reverting to the examination of the idea which I had of a Perfect Being, I found that in this case existence was implied in it in the same manner in which the equality of its three angles to two right angles is implied in the triangle; or in the idea of a sphere, that all the points on its surface are equidistant from its centre, or even more evidently still. Consequently it is at least as certain that God who is a Being so perfect, is, or exists, as any demonstration of geometry can be. (277)

Descartes Perfect Being exists the way a triangle exists—it must exist the way a triangle has two right angles. In other words, God must be presupposed the same way one presupposes the principles and axioms of mathematical truths. Descartes is aware that such a rational attempt may not be very convincing for some. Following his method of extreme doubt, Descartes shifts his approach and asks about the reliability of our thoughts during a dream. Can we doubt our thoughts and imagination the same way that we doubt our senses? Descartes provides this answer,

And though the wisest minds may study the matter as much as they will, I do not believe that they will be able to give any sufficient reason for removing this doubt, unless they presuppose the existence of God. For to begin with, that which I have just taken as a rule that is to say, that all the things that we very clearly and very distinctly conceive of are true, is certain only because God is or exists and that He is a Perfect Being, and that all that is in us issues from Him. (277, emphasis added)

Notice what Descartes is saying here—one must presuppose God exists because God is a Perfect Being which must include existence. In other words, God is (presupposition), therefore God exists (because a Perfect Being must exist). This is the heart of the presuppositional approach. And it is entirely circular in reasoning. But before we get to the analysis of Descartes approach and the presuppositional method, it is best to look at his basic points of departure.

To summarize, Descartes reasoning is as follows: one can not trust the senses because the senses can be wrong. However, as Descartes famously observes “I think therefore I am”, and he concludes that he can in fact trust his reasoning, because he has to exist in order to think (275, 276). Further, Descartes thinks that because he can think of a Perfect Being, God must exist. God must exist because existence is a property of Being and in order to be the most Perfect Being, such a Being must have the property of existence. Descartes calls this a “metaphysical certainty” (277). If one doubts such a metaphysical certainty, they should presuppose God exists because he reasons that God’s existence will solve the doubts one can experience from thoughts, dreams, imagination, or the senses. In other words, one must presuppose that God exists in order to make sense out of the reality of the world. Descartes makes this even more clear in his Meditation on First Philosophy,

And we must not object that it is in truth necessary for me to assert that God exists after having presupposed that He possesses every sort of perfection, since existence is one of these (320).

For Descartes, God exists because it is presupposed that God has perfection. It is worth pointing out that not every theist that holds to the ontological argument, or Perfect Being theology, is a presuppositionalist or must be a presuppositionalist in order to defend it. Here, I am merely pointing out that Descartes does make his presupposition of God’s existence a central point in his argument for God’s existence. Descartes needs to make this philosophical assertion because he can not start with the trust worthiness of Being or reality itself (for him, those things must be doubted). His argument must be purely rational because that is the only starting point that will provide certainty for him. Descartes philosophical theology is unique in the sense that he does not take Being as his starting point but focuses on rational geometrical proofs and the need to presuppose the existence of God as the foundation of his method. For Descartes, God is a Perfect Being which must be presupposed.

Now a few concluding thoughts about Descartes and presuppositionalism can be said. First, there is nothing inherently wrong with a pure rational argument for God’s existence. Plato would have have agreed with some of Descartes ideas. Many mathematicians have come to theistic conclusions based on the symmetry and principles of math itself. Many, I think, are valid. The problem is that starting with the existence of God and then arguing from that point is bad logic. The thing that always prevented me from taking the presuppositional school of apologetics seriously is the the circularity of the method. Circular reasoning is a logical fallacy which is formally called the petitio principii (begging of the question). This is an error that occurs when when the conclusion of an argument is already present, usually disguised or vague, in the premises. It is seen as circular because the conclusion is present in the premises, and no real progress is made. A more modern example of circular reasoning is this, “You can’t expect seventeen-year-olds to vote intelligently, because they are too young to have good judgment about the issues.” The conclusion of the argument is one of its premises. When the conclusion is one of the premises, the argument is circular and begs the question. Descartes reasoning that God must be presupposed to show that God exists is circular. Finally, it makes little practical sense to tell the non-theist that they must presuppose the existence of God when the existence of God is the central question.

There is another issue with rationalism more generally. Much of modern philosophy, beginning with Descartes begins with epistemology (how we know what we know). When one begins with how we know, and not the metaphysical givenness of reality, a pure rational epistemology can quickly go circular. Descartes gets things only half right here. Existence is a property of being. But there are different orders of being and different kinds of existence. My thought of a flying unicorn with laser beams shooting out its eyes has a very different kind of being than the tree in front of my house. Imagination presents a different mode of being than physical reality. Angels have a very different kind of being than I do. There are different orders to being and different kinds of existence. Descartes is making a rational or conceptual statement and applying it to concrete reality, when in fact, the question really is whether or not such a Perfect Being exists absolutely, not rationally or conceptually. The theist and non-theist can both have the same conception of a Perfect Being but the issue at stake is whether or not such a being actually exists. Starting with what-is and understanding the order of being (and order of knowing) is a far more fruitful project.

It is worth noting here that Benedict Spinoza assumes much of the Cartesian methodology and presuppositions. However, Spinoza was lead through his rational conception of Perfect Being theology that God and the world are one. For Spinoza, pantheism was the logical outcome based on his Cartesian rationalism and presuppositions. Presupposing the existence of God on strict rational grounds does not prevent one from becoming a pantheist. In other words, presupposing that God exists does not necessarily lead one to Christian theism.

As I will always try to explain, when one begins with epistemology, and make that one’s starting point, instead of metaphysical realism, or the givenness of Being, things go bad in philosophy and one’s approach to apologetics.

1Benedict Spinoza in his Ethics often assumes Descartes’s presuppositional outlook, but I hope to develop that later. Interestingly, the father of presuppositionalism, Van Til, developed his school of apologetics based on ethical concerns.

Works Cited

Descartes, Rene. Bacon, Descartes, Spinoza. Great Books of the Western World. Vol. 28. Encyclopedia Britannica, Inc., 1999.