Editor’s Note: This essay is the first in a two-part series on Descartes’ Meditations. The second essay is here.
In an era of great debate over the fundamental facts of nature—e.g., about the Earth’s place in the cosmos, the amount of energy in the universe, the circulation of blood in the human body—René Descartes’ (1596-1650) central goal was to establish a body of scientific knowledge that held the same degree of certainty as mathematical truths.
The Meditations on First Philosophy (1641) is a classic work that lays the philosophical foundations of this enterprise. It raises timeless and fundamental philosophical questions about knowledge, the self, the mind and its relation to the body, substance, causality, perception, ideas, the existence of God, and more.
This two-part essay reviews Descartes’ process of reasoning and some of his arguments on these issues.
1. Meditation 1: Skepticism and the Method of Doubt
Descartes begins by reflecting on the unfortunate fact that he has had many false beliefs. He sets out to devise a strategy to not just prevent having false beliefs but, more dramatically, to ensure that scientific research reveals truth, not error.
To avoid any false beliefs, his strategy is to doubt any belief he has that could be false or that he could be mistaken about.
His senses have deceived him before, so they could be deceiving him now, so he rejects all sensory-based beliefs. He reasons that if an alleged source of knowledge is sometimes deceptive, then it could always be deceptive, and so it should be rejected to find beliefs that cannot be false.
He realizes that if he were asleep and dreaming, many of his beliefs would be false: e.g., if he were dreaming about walking somewhere, his belief that “he is walking,” would be false. Since he cannot ever tell if he is dreaming or not, this is further reason to doubt any beliefs from his senses: dreams appear the same as genuine experiences: they cannot be distinguished.
He also realizes that he could be mistaken even about beliefs that seem clearly true to him, whether awake or dreaming, e.g., that “bachelors are unmarried.” He could be mistaken, even about such beliefs, because he could be being deceived by some evil genius or even God: this is possible and he cannot show that it is not his actual situation. Since Descartes wishes to reject any belief that could be false, that he could be mistaken about, he rejects even these beliefs.
The sciences, however, rely on beliefs not only about the physical world but also about mathematics, and by the end of Meditation 1, Descartes is tempted to rid himself of the desire to acquire knowledge altogether.
2. Meditation 2: The Essence of the Human Mind
In an epistemological epiphany, Descartes notices that one of his beliefs cannot be doubted and is therefore certain:
“I am, I exist, is necessarily true each time that I pronounce it, or that I mentally conceive it.”
Descartes simply recognizes that he exists as long as he is thinking. This is true even when he’s dreaming and even if he were deceived by an evil demon or even God. Whenever there are thoughts, those thoughts (and their thinker) exist, even if those thoughts are within a deception. This is the Cogito as it is given in the Meditations.
So, Descartes knows that he exists, but what kind of a thing is he? He can conceive of himself existing without a body, but cannot conceive of himself existing without thought. So, he must be a thinking thing: something doubting, understanding, affirming, denying, willing, imagining and feeling. Descartes takes this to mean that he is essentially a mind and not a body.
How does the Cogito escape the net of doubt cast in Meditation 1? Descartes says that judgments about his own thoughts are entirely unproblematic; the contents of his mental states are clear to him, meaning that he can clearly tell what his own beliefs are. However, even granted this “transparency” of mental states, how does he know that there is a single entity that is the subject of all of his thoughts? Descartes asks rhetorically, “Am I not the same who now doubts nearly everything, who still understands something; who affirms that this one thing is true?” His unstated answer is that he is a single entity that endures over time.
3. Meditation 3: The Existence of God
Being a thinking thing, Descartes knows that he has ideas. He notices that one of these ideas is the idea of God, i.e., something eternal, infinite, all-knowing, all-powerful, all-good, and the creator of all things. But where did he get this idea of God, a perfect being? Did he invent it? Did it come from other people? No. His idea of God could only have come from God. According to Descartes, a cause must be at least as real or perfect as its effect. The idea of God however represents much more reality and perfection than the idea of himself, or of anything else. There’s only then one possible cause: God. So, God exists. This is Descartes’ causal argument for God’s existence.
However, God might be a deceiver: God could have made Descartes have many false beliefs. That’s possible. How then can Descartes be sure that he can trust any of his other beliefs besides the belief of his own existence? In the case of the Cogito, Descartes saw very “clearly and distinctly” that to think, one must exist. But how does he know that clear and distinct perception is always reliable? E.g., how does he know that “triangles have three sides” if there’s an evil demon deceiving him?
He now realizes that there is no way that an all-good being would make it so that when he “clearly and distinctly” thinks something to be true that it wouldn’t be true: an all-good being would not deceive him or allow an evil demon such license. Plus, he’s just proven that God exists. So now he can trust that whenever he “clearly and distinctly” thinks something to be true, it is.
 For Descartes, knowledge of the sort that can serve as a foundation for science requires certainty, which in turn requires indubitability, namely, that it can’t be rationally doubted. This is a very high standard for knowledge, and important to understand because it’s directly relevant to responses to Cartesian skepticism that deny the indubitability requirement.
 Many of Descartes’ other works, such as The World, Treatise on Man, Description of the Human Body, and Optics, focused on providing the scientific content itself. See Descartes: The World and Other Writings, ed. Stephen Gaukroger (Cambridge, 1998).
 “Several years have now passed since I first realized how numerous were the false opinions that in my youth I had taken to be true, and thus how doubtful were all those that I had subsequently built upon them. And thus I realized that once in my life I had to raze everything to the ground and begin again from the original foundations, if I wanted to establish anything firm and lasting in the sciences” (Med. 1). Descartes was in his mid-30s by this point.
 “I see so plainly that there are no definitive signs by which to distinguish being awake from being asleep” (Med. 1).
 “Whether I am awake or asleep, two and three added together are five, and a square has no more than four sides” (Med. 1). Such beliefs are typically called analytic a priori, since they are not based in sense-experience, and can be known purely by definition or reason.
 Sometimes translated as “malicious demon.” The Latin is genium malignum. I prefer “genius” to “demon,” since the latter has a religious connotation, but at this point in the Meditations religious belief of any kind is still in doubt.
 “I am not unlike a prisoner who enjoyed an imaginary freedom during his sleep, but, when he later begins to suspect that he is dreaming, fears being awakened and nonchalantly conspires with these pleasant illusions” (Med. 1).
 Interestingly, the famous inference cogito ergo sum (“I think therefore I am”) occurs in Descartes’ Discourse on the Method (Part IV) and the Principles of Philosophy (I.7), but not so in the Meditations. It’s not clear why Descartes doesn’t do so in the Meditations. Some commentators argue that given his method of doubt in the Meditations, even simple inferences are put in question. That is, at this stage of the work, Descartes is not even sure that logic is reliable, and so cannot legitimately argue from premises to a conclusion that he exists. Another way to explain the absence of the ergo is to point out that Descartes is seeking a foundational belief upon which to justify all of his other beliefs and therefore ground knowledge, and that for a belief to be properly foundational it must not stand in need of justification itself.
 To say that he is essentially a mind and not a body is to say that his mind is part of his essence: if his mind ceased to exist, he would cease to exist, but he could exist without his body, so it is not part of his essence. Descartes also argues in Med. 2 that his knowledge of his mind through non-sensory means is also the best way to know his body. To show this, he uses the example of a piece of wax. Even when its sensory properties change (through melting, hardening, changing color, etc.) it remains the same piece of wax. So, the wax itself cannot be known through the senses. Also, the true essence of the wax is known through the senses, for the wax can take on a great, perhaps infinite, variety of shapes.
 As for his reasoning, Descartes is probably appealing to the fact that he experiences himself as a single entity through time. Immanuel Kant will famously challenge this line of reasoning in the Paralogisms of Pure Reason in his Critique of Pure Reason (1781).
 According to Descartes, each thing is “assigned” a degree of reality (which corresponds to its perfection, that is, its capacity to exist independently). In other words, everything has a place on the hierarchy of reality. God, of course, is at the “top,” since he is the most perfect, most independent being possible, and so has the greatest degree of reality.
 He asks: “What is required for knowledge is my simply having a clear and distinct perception of what I am asserting. Surely it’s not possible that I could have a clear and distinct perception of the truth of some judgment (proposition) which turned out to be false?” (Med. 3). For this reason, Descartes is often called a “rationalist,” since clear and distinct perception, upon which all knowledge ultimately rests on, is not a form of sense-experience.
 Descartes defines God as all-good. But in Meditation 1, he mentions that being “all-good” doesn’t automatically rule out some deception on God’s part. Even the Bible seems to depict God as a father who lets his children (us) be deceived sometimes. If God allows us to be deceived sometimes, why couldn’t he allow us to be deceived all of the time? But at this point in Meditation 3, he realizes that such a worry was overblown, for he now clearly and distinctly perceives that God would not allow us to be deceived in such a sweeping manner.
 We can now see the so-called “Cartesian Circle.” Descartes wants to remove the possibility that there can be a deceiving God or an evil demon deceiving him. To do this, he first argues that God exists and second claims that God couldn’t be a deceiver. Now to show that God exists he says that he clearly and distinctly perceives a causal principle (that there is as much actual reality in a cause as there is representative reality in its effect). And to show that God is not a deceiver he says that he clearly and distinctly perceives that deception is incompatible with perfection. But remember why Descartes is trying to prove that God couldn’t be a deceiver: in order to validate his provisional general rule that he can trust clear and distinct perception! See the circle?
External World Skepticism by Andrew Chapman
Modal Epistemology: Knowledge of Possibility & Necessity by Bob Fischer
Philosophy and Its Contrast with Science by Thomas Metcalf
About the Author
Marc Bobro is Professor and Chair of Philosophy at Santa Barbara City College in California. He holds a PhD in philosophy from the University of Washington, Seattle, an MA in philosophy from King’s College London, and a BA in philosophy from the University of Arizona, Tucson. He specializes in the history of modern philosophy, especially Leibniz. Bobro is also the bassist and tubist for the mythopoetic punk band Crying 4 Kafka and collaborates on art with Elizabeth Folk. https://marcbobro.academia.edu