Proving the Existence of God: Defending Descartes’ Causal Argument

A staunch belief in a God is often seen as irrational. But a staunch disbelief in God is also seen as irrational. Instead, many would state that a belief in God cannot be proven definitively true or definitively false. If a belief in God is rational, it is only rational on the grounds of empirical evidence and/or reason. Whether this judgment of the rationality of a theistic faith is justifiable, let us assume for the sake of this article that it is. Contrary to popular belief, belief in God was not always so blind and utterly removed from reason as we might assume. In 1647, René Descartes, the French philosopher, published Meditations on First Philosophy in Latin. Through this philosophical work, Descartes sought to prove by reason alone the existence of God and the immortality of the soul. Descartes was in fact prompted by rationalism, the view that truth can be derived by sheer reasoning, to disregard all sensory perceptions, lest they be illusionary. Consequently, without appealing to sensory perceptions, Descartes’ Meditations offers three rational arguments for the existence of God, the first of which is often called “the causal argument.” The premises of his argument as it stands are not irrefutable. Nevertheless, his premises allow for changes to maintain the truth of the conclusion. These changes do not modify his argument to falsely fit his conclusion. Instead, they address loopholes and offer modern day readers a way in which reason alone may lead to an understanding of God’s existence.

Descartes’ causal argument relies on two major premises that supposedly lead to his conclusion.

Premise 1: “The objective reality of any of our ideas requires a cause which contains the very same reality, not merely objectively but formally or eminently.”[i]

In other words, the reality of any representative idea in the intellect must have been caused by something that exists outside of the intellect, which either contains the same amount of reality as the idea or even more.[ii]

Premise 2: “We have an idea of God and the objective reality of [our idea of God] is not contained in us either formally or eminently.”[iii]

Put simply, the reality that our idea of God represents cannot be one conjured by us, nor by our own thoughts. Moreover, nothing could formally or eminently possess the attributes contained objectively in the idea without being God. For something to possess the attributes of our idea of God formally would be for something to actually, or perhaps already, possess those attributes. For something to possess the attributes of God eminently would be for something to be capable of possessing those attributes, without necessarily already possessing those attributes.

Therefore, since all ideas require a cause, and the cause for the idea of God exists outside of us, only God himself could contain the reality that the idea of God represents.

Conclusion: God exists.

Is it that simple? No. Under critical analysis, this progression of logic fails to prove God’s existence for two reasons. Firstly, according to Descartes, a perception is only clear if it is “present and accessible to the attentive mind,” and distinct if “it is so sharply separated from all other perceptions that it contains within itself only what is clear.”[iv] If some ideas, which are not clear and distinct by Descartes’ standards, do not require causes, Premise 1) no longer holds true. This is because the idea of God would not need to be caused by God himself. Instead, the idea of a divine being, being perhaps unclear and indistinct, would be caused by something other than that being itself. Secondly, if we ourselves, as substances, can eminently cause all ideas, as long as these ideas are made up of the qualities found in substances, Premise 2) is also false. After all, it might be possible that the ideas we have of God and all other things are simply creative combinations of mental or physical qualities that we have found in ourselves, such as intelligence, shape, extension, etc. Accordingly, we could have caused the idea of God, as opposed to God himself. To save Descartes’ argument from the errors of his two major premises, both Premise 1) and Premise 2) must be modified without changing Descartes’ intended argument. Furthermore, an additional premise, implicit in Descartes’ original argument, must precede his second. Fortunately, these changes are not only essential but also justifiable. With these changes, Descartes’ argument logically proves that God exists.

Two assumptions underline Premise 1). Prior to Descartes’ main claim that any objective reality is an effect of a formal or eminent reality, he asserts that the “mode of being by which a thing exists objectively <representatively> in the intellect by way of an idea…is certainly not nothing.”[v] By the natural light (of reason and/or of God), Descartes also assumes that anything that exists, even if only as an idea, cannot come from nothing.[vi] Descartes refutes this second assumption, however, by offering the idea of cold as an example of an objective reality that represents a “non-thing,” namely the absence of heat.[vii] Even though his mind represents the idea of cold as “something real and positive,” the cold is only a material falsity and can only “arise from nothing.”[viii] If the idea of cold is materially false, so could the idea of God be materially false and not require a cause. If the idea of God has no real cause, Descartes’ Premise 2)— that the cause of the objective reality of his idea of God is not found in us—would no longer be meaningful, since the cause would not exist.

Therefore, Premise 1) can reclaim its truth if it instead states, “the objective reality of any of our ideas [that are clear and distinct] requires a cause …,” for unlike the ideas of heat and cold, “[the idea of God] is utterly clear and distinct.”[ix] This modified Premise 1), however, can only apply to the idea of God in Premise 2) if Premise 2) is also modified as follows: “we have a [clear and distinct] idea of God…”[x] Remember that Descartes defines a perception as clear if it is present and accessible, and distinct if it can be sharply separated from all other perceptions. Thus, the validity of the new Premise 2) now rests on whether or not the idea of God is indeed clear and distinct.

Unfortunately, the two ways in which Descartes defends his idea of God as “clear and distinct” are unsatisfactory. He first claims to “clearly understand that there is more reality in an infinite substance than in a finite one” in order to negate the possibility that the idea of God “represents something unreal.”[xi] In other words, an infinitely large house has more reality for Descartes than the finitely large house you and I may live in. For this claim to be valid, reality must be quantifiable, rather than absolute. Indeed, Descartes has been said to fall in the tradition of accepting the idea of degrees of reality; while humans are real, God and angels of greater perfection are more real.[xii] At the outset, however, this appears unreasonable; an object, once real, cannot be made more or less real. The only way reality can be quantified is if an infinitely large house contains more reality by consisting of more real materials, like bricks and tiles, and taking up more real space. Even if Descartes intended this interpretation of reality, more reality in the idea of God does not in fact guarantee a clearer and more distinct idea. After all, he found his idea of cold to lack clarity or accessibility as a mere material falsity, in spite of the “real and positive” quality of his idea.[xiii] Therefore, the reality of the idea of God has little to do with its clarity and distinctness.

Descartes again unsuccessfully defends his idea of God as clear and distinct, when asserting that “it is enough that I understand the infinite, and that I judge that all the attributes which I clearly perceive and know to imply some perfection—and perhaps countless others of which I am ignorant—are present in God either formally or eminently to make the idea … of God … clear and distinct.”[xiv] If, however, certain attributes of God are not and can never be accessible to him by his own definition of clear perception, he can never have a clear idea of God.[xv] He claims he can “understand the infinite,” and therefore access the infinite without truly grasping it, as one can touch a mountain without embracing it.[xvi] This mountain analogy does not suffice here, though.[xvii] A mountain cannot be embraced due to its sheer size, like God’s infinite nature. The sides of the mountains, however, are still within reach to a human being, while all of God’s attributes are infinite and should be inaccessible to Descartes, a finite being. Descartes believes he understands God’s infiniteness by acknowledging that some attributes of God are inaccessible. This is precisely what prevents him from having a “clear” understanding of the idea of God, however. Since his “perception… cannot be distinct without being clear,” Descartes’ idea of God, according to his own defense, is neither clear nor distinct.[xviii]

Based on both of Descartes’ defenses, the modified Premise 2) appears unjustifiable. Nevertheless, the idea of God cannot be so easily deemed inaccessible and unclear because it is a mere absence. While the absence of heat can only lead to cold, an absence of finiteness can be construed in two ways—nothingness or infiniteness. The infinite nature of God is certainly not equal to nothingness. Consequently, unlike the idea of cold, the idea of God cannot be a total absence. On the other hand, God’s infinite nature cannot simply be an inaccessible, unclear absence of boundaries. Just as the nature of heat consists of more energy and activity in atoms than the nature of cold, the nature of infiniteness, within our own space-time continuum, would consist of more energy and activity than anything finite. For example, drawing a finite line requires one to actively stop drawing and create an absence of line that an infinite line would not have. Therefore, the idea of God cannot be a mere absence, like the idea of cold, and in that sense can indeed be accessible to the attentive mind.

Likewise, although Descartes’ incomplete understanding of God may prove that God’s infinite nature is inherently inaccessible to finite beings like ourselves and therefore unclear, the idea of God’s infinite nature must be at least somewhat accessible to Descartes if the idea is conceivable at all. Of course, this might imply that every idea, even the idea of cold, must be conceived and accessed by us and is therefore clear. Descartes’ idea of cold was deemed unclear by Descartes himself, however, only because it represented an absence. Since we can be sure that the idea of God cannot simply be an absence of boundaries, Descartes’ idea of cold is accessible, because it is conceivable; his idea of cold is not an idea of an absence, which would be impossible to be clear.

Of course, we cannot modify Premise 2) to be “we have a [clear and distinct] idea of God,” unless this modified Premise 2) is in fact true. Thus, we still need to prove that the idea of God is distinct. By the definition of God as “infinite, <eternal, immutable,> independent, supremely intelligent, supremely powerful, and which created both myself and everything … that exists,” there cannot possibly be another perception that overlaps with this one.[xix] If there is another idea of a being that shares God’s supreme power, this being would naturally encompass the power of the first idea of God, making the first idea of God no longer supremely powerful. Similarly, if another being could have “created both myself and everything … that exists,” the original idea of God could not also have created everything. Therefore, as long as the idea of God is clear, by definition, it is also distinct from all other perceptions.

Consequently, the idea of God is clear and distinct, justifying the modified Premise 2) that “we have a [clear and distinct] idea of God.” It now follows from the modified Premise 1) and Premise 2) that all clear and distinct ideas require a formal and eminent cause, that we have a clear and distinct idea of God, and that the idea of God, therefore, does require a formal or eminent cause. Since Premise 2), that “the objective reality of [our idea of God] is not contained in us either formally or eminently,” assumes that a cause for Descartes’ idea of God does exist, both modifications to his premises necessarily fix the initial loophole in Premise 1) to maintain the truth of this assumption.

Although this assumption of Premise 2) is now justified, like the original Premise 1), Premise 2) still falls short in its second assumption, namely that some causes of ideas cannot originate in ourselves. Descartes suggests that this key assumption in Premise 2) is false, because although we are thinking substances and therefore do not possess qualities of corporeal beings like “extension, shape, position, and movements,” because we ourselves are substances, we are able to cause the elements or qualities of corporeal beings.[xx] In other words, because Descartes himself is a substance, just as he does not need to possess “the clear and distinct elements in my ideas of corporeal things” in order to be their eminent causes, he may also not need to possess the clear and distinct elements of his idea of God to be its eminent cause, provided that the elements of God are elements of substance, duration, or number that can arise from himself.xxi Since Descartes explicitly calls God a substance, the objective reality of the idea of God can easily be a mere effect of thought. Therefore, Premise 2)’s claim that “the objective reality of [our idea of God] is not contained in us either formally or eminently” cannot be true. Instead, Descartes would only be able to conclude that the objective reality of his idea of God can be contained in us. Therefore, God cannot exist.

Fortunately, the loophole in Descartes’ second assumption is inconsistent with our true thinking capacity, and his Premise 2) can still be true and clarified by an additional preceding premise. Descartes ignores the fact that if we possess the potential to produce all elements of substances without possessing them formally, we should be able to create new shapes, colors, and forms of movement at any moment at will. Despite this, when I try to conjure in my mind other elements and modes of substance not already mentioned, I fail to be able to do so. This suggests that shapes, colors, duration, and other corporeal do indeed exist outside of us. Therefore, a preceding premise, that we ourselves cannot be the formal or eminent causes of all objective reality, is not only true, but also necessary to explicitly close the loophole in Premise 2).

Now, according to the two modifications of the first and second premises, the clear and distinct idea of God requires a cause with the same reality as the idea, either formally or eminently. According to the added preceding premise to Premise 2), because we, thinking substances, cannot be the formal or eminent causes of all objective reality, it is necessary for the cause of the idea of God to not be found in us. Given that it is possible and evident that the cause of the idea of God is not contained in us, the cause of the idea of God must be contained outside of us, as God himself.

Descartes’ original premises could not logically lead to his conclusion for two reasons. First, he allowed for the possibility that the idea of God, like the idea of cold, did not need a cause at all. Second, he suggested that all ideas, including the idea of God, could in fact be caused by ourselves. These loopholes require us to modify both premises and supply an additional preceding premise to the second, and this modified argument allows us to make the logical inference that Descartes originally wanted to make. These changes facilitate a sturdier and more truthful argument, proving that God exists by Descartes’ causal argument.

Descartes’ work offers an enlightening perspective on the commonly spouted claim that Christianity is a game of blindness. Common modern beliefs about religion assume that we cannot by reason alone prove that God exists nor that he does not exist. Instead, faith, a separate mode of thought altogether, must be applied to conclusions about God that reason alone cannot bring about. However, Descartes’ reliance on and confidence in human reason radically opposes modern assumptions about reason and faith. Instead, he esteems reason so much that he argues that reason is not just compatible with faith. He in fact seeks to use reason alone to argue for and justify faith in God. While Descartes’ original argument may not be bulletproof, it is nonetheless redeemable. Therefore, neither his argument nor his conclusion should be immediately rejected. Instead, we ought to reconsider the vital, and perhaps essential, role of rational thinking in the pursuit of truth about God’s existence.


i. René Descartes, Philosophical Writings of Descartes: Volume 2, trans. John Cottingham, Robert Stoothoff, Dugald Murdoch (Cambridge: Cambridge University Press, 1985), 118.
ii. Descartes, Volume 2, 28-29.
iii. Descartes, Volume 2, 118.
iv. René Descartes, Philosophical Writings of Descartes: Volume 1, trans. John Cottingham, Robert Stoothoff, Dugald Murdoch (Cambridge: Cambridge University Press, 1985), 208.
v. Descartes, Volume 2, 29.
vi. Descartes, Volume 2, 29.
vii. Descartes, Volume 2, 30.
viii. Descartes, Volume 2, 30.
ix. Descartes, Volume 2, 31, 118.
x. Descartes, Volume 2, 118.
xi. Descartes, Volume 2, 31.
xii. Special thanks to Samuel Levey for his helpful comments.
xiii. Descartes, Volume 2, 30.
xiv. Descartes, Volume 2, 32.
xv. Descartes, Volume 1, 208.
xvi. Descartes, Volume 2, 32.
xvii. Descartes, Volume 2, 32.
xviii. Descartes, Volume 1, 208.
xix. Descartes, Volume 2, 31.
xx. Descartes, Volume 2, 31.
xxi. Descartes, Volume 2, 30.

Jessica Tong ’17 is from Sydney, Australia. She is a Philosophy major and a Government minor.

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