The Meditations consist of the presentation of Descartes' metaphysical system in its most detailed level and in the expanding of Descartes' philosophical system, which he first introduced in the fourth part of his Discourse on Method (1637). Descartes' metaphysical thought is also found in the Principles of Philosophy (1644), which the author intended to be a philosophy guidebook.
The first way that Descartes tries to undermine his beliefs is by considering the fact that he remembers that his senses have deceived him before. If he has been misled by sensory information in the past (e.g. he judged that the stick in the water was bent, when in fact it was straight), then he may be deceived now, "and it is prudent never to trust completely those who have deceived us even once."
He goes on to suggest more powerful reasons to doubt that his beliefs are true. In general, his method is that of forming skeptical hypotheses — methodic doubt. In the first meditation, he considers whether he is mad, dreaming, or deceived by an evil demon. If any of these scenarios were the case, many of his beliefs would be false.
The general form of these arguments is:
Descartes' goal — as stated at the beginning of the meditation — is to suspend judgment about any of his beliefs which are even slightly doubtful. The skeptical scenarios show that all of the beliefs which he considers in the first meditation, including at the very least all of his beliefs about the physical world, are doubtful. So he decides to suspend judgment. He will henceforth give up all of his beliefs about the physical world. This is very difficult. At the end of the first meditation Descartes compares himself to a prisoner who enjoys an imaginary freedom while asleep, and dreads waking. In the same way Descartes slips back into his old beliefs, and dreads waking to toil "amid the inextricable darkness of the problems [he has] now raised."
It is important to keep in mind when reading the Meditations that Descartes intends to lead the reader along with him gradually. He begins with skepticism and attempts to offer a solution. Thus, he should not be uncharitably read as contradicting himself when, for instance, he thinks something is doubtful in the first meditation and as certain in the last. Several of his objectors fail to read the meditations as a guide, in which the order of the arguments is important, and so make this mistake.
In Meditation II: Concerning The Nature of the Human Mind: That It Is Better Known Than The Body, Descartes lays out a pattern of thought, sometimes called representationalism, in response to the doubts forwarded in Meditation I. He identifies five steps in this theory:
Descartes argues that this representational theory disconnects the world from the mind, leading to the need for some sort of bridge to span the separation and provide good reasons to believe that the ideas accurately represent the outside world. The first plank he uses in constructing this bridge can be found in the following excerpt:
I have convinced myself that there is nothing in the world - no sky, no earth, no minds, no bodies. Doesn't it follow that I don't exist? No, surely I must exist if it's me who is convinced of something. But there is a deceiver, supremely powerful and cunning whose aim is to see that I am always deceived. But surely I exist, if I am deceived. Let him deceive me all he can, he will never make it the case that I am nothing while I think that I am something. Thus having fully weighed every consideration, I must finally conclude that the statement "I am, I exist" must be true whenever I state it or mentally consider it. (Descartes, Meditation II: On the Nature of the Human Mind, Which Is Better Known Than the Body).
In other words, one's consciousness implies one's existence. In one of Descartes' replies to objections to the book, he summed this up in the phrase, I am, I exist, which is often confused with the famous quote, I think, therefore I am.
Once he has secured his existence, however, Descartes seeks to find out what "I" is. He rejects the typical method which looks for a definition, e.g. Rational Animal, because the words used in the definition would then need to be defined. He seeks simple terms that do not need to be defined in this way, but whose meaning can just be "seen." From these self-evident truths, complex terms can be built up.
The first of these self-evident truths is Descartes' proof of existence turned on its head:
But what then am I? A thinking thing. And what is that? Something that doubts, understands, affirms, denies, wills, refuses, and also sense and has mental images. (Descartes, Meditation II: On the Nature of the Human Mind, Which Is Better Known Than the Body).
To define himself further, Descartes turns to the example of wax. He determines that wax isn't wax because of its color, texture or shape, as all of these things can change and the substance still be wax. Therefore, he distinguishes between ordinary perception and judgement. The reality of the wax is "grasped, not by the senses or the power of having mental images, but by the understanding alone." When one understands the mathematical principles of the substance, such as its expansion under heat, figure and motion, the knowledge of the wax can be clear and distinct.
If a substance such as wax can be known in this fashion, then the same must be of ourselves. The self, then, is not determined by what we sense of ourselves - these hands, this head, these eyes - but by simply the things one thinks. Thus, one "can't grasp anything more easily or plainly than [his] mind."
Descartes concludes that he exists because he is a "thinking thing." If he is the thing that can be deceived and can think and have thoughts, then he must exist. Thus his famous quote "I think, therefore I am."
Descartes proposed that there are three types of ideas: Innate, Invented, and Adventitious. Innate ideas are and have always been within us, Fictitious or invented ideas come from our imagination, and Adventitious ideas come from experiences of the world. He argues that the idea of God is Innate and placed in us by God and he rejected the possibility that the idea of God is Invented or Adventitious.
Descartes argued that he had a clear and distinct idea of God. In the same way that the cogito was self-evident, so too is the existence of God, as his perfect idea of a perfect being could not have been caused by anything less than a perfect being.
The conclusions of the previous Meditations that "I" and "God" both exist lead to another problem: If God is perfectly good and the source of all that is, how is there room for error or falsehood? Descartes attempts to answer this question in Meditation IV: On Truth and Falsity.
If I've gotten everything in me from God and He hasn't given me the ability to err, it doesn't seem possible for me ever to err. (Descartes, Meditation IV: On Truth and Falsity).
The framework of his arguments center on the Great Chain of Being, in which God's perfect goodness is relative to His perfect being. On the extreme opposite end of the scale is complete nothingness, which is also the extremity of evil. Thus, humans are an intermediary between these two extremes, being less "real" or "good" than God, but more "real" and "good" than nothingness. Thus, error (as a part of evil) is not a positive reality, it is only the absence of what is correct. In this way, its existence is allowed within the context of a perfectly inerrant God.
I find that I am "intermediate" between God and nothingness, between the supreme entity and nonentity. Insofar as I am the creation of the supreme entity, there's nothing in me to account for my being deceived or led into error, but, inasmuch as I somehow participate in nothing or nonentity - that is, insofar as I am distinct from the supreme entity itself and lack many things - it's not surprising that I go wrong. I thus understand that, in itself, error is a lack, rather than a real thing dependent on God. Hence, I understand that I can err without God's having given me a special ability to do so. Rather, I fall into error because my God-given ability to judge the truth is not infinite. (Descartes, Meditation IV: On Truth and Falsity).
Descartes also concedes two points that might allow for the possibility of his ability to err. First, he notes that it is very possible that his limited knowledge prevents him from understanding why God chose to create him so he could make mistakes. If he could see the things that God could see, with a complete and infinite scope, perhaps he would judge his ability to err as the best option. He uses this point to attack the Aristotelian structure of causes. The final cause described by Aristotle are the "what for" of an object, but Descartes claims that because he is unable to completely comprehend the mind of God, it is impossible to completely understand the "why" through science - only the "how."
I realize that I shouldn't be surprised at God's doing things that I can't explain. I shouldn't doubt His existence just because I find that I sometimes can't understand why or how He has made something. I know that my nature is weak and limited and that God's is limitless, incomprehensible, and infinite, and, from this, I can infer that He can do innumerable things whose reasons are unknown to me. On this ground alone, I regard the common practice of explaining things in terms of their purposes to be useless in physics: it would be foolhardy of me to think that I can discover God's purposes. (Descartes, Meditation IV: On Truth and Falsity).
Second, he realized that God has the ability to create a large number of things of which he would just be a part. Perhaps the error is only apparent when looking at the individual and is reconciled when looking at the whole.
When asking whether God's works are perfect, I ought to look at all of them together, not at one isolation. For something that seems imperfect when viewed alone might seem completely perfect when regarded as having a place in the world. Of course, since calling everything into doubt, I haven't established that anything exists besides me and God. But, when I consider God's immense power, I can't deny that He has made - or, in any case, that He could have made - many other things, and I must therefore view myself as having a place in a universe. (Descartes, Meditation IV: On Truth and Falsity).
Lastly, Meditation IV attributes the source of error to a discrepancy between two divine gifts: understanding and will. Understanding is given in an incomplete form, while will (by nature) can only be either completely given or not given at all. When he is presented with a certain amount of understanding and then chooses to act outside of that, he is in error. Thus, the gifts of God (understanding and will) both remain good and only the incorrect usage by him remains as error.
If I suspend judgement when I don't clearly and distinctly grasp what is true, I obviously do right and am not deceived. But, if I either affirm or deny in a case of this sort, I misuse my freedom of choice. If I affirm what is false, I clearly err, and, if I stumble onto the truth, I'm still blameworthy since the light of nature reveals that a perception of the understanding should always precede a decision of the will. In these misuses of freedom of choice lies the deprivation that accounts for error. And this deprivation, I maintain, lies in the working of the will insofar as it comes from me - not in my God-given ability to will, or even in the will's operation insofar as it derives from Him. (Descartes, Meditation IV: On Truth and Falsity).
Meditation V: Concerning the Essence of Material Things, and Again Concerning God, That He Exists begins with the stated purpose of expanding the "known items" of God and self to include outside material objects, Descartes saves that for Meditation VI in lieu of something he deems more fundamental but in the same direction: a discussion concerning the ideas of those external items. Along the way, he stumbles upon another claimed logical proof of God's existence.
Before asking whether any such objects exist outside me, I ought to consider the ideas of these objects as they exist in my thoughts and see which are clear and which confused. (Descartes, Meditation V: On the Essence of Material Objects and More on God's Existence).
In pondering these ideas of external objects, Descartes realizes they can be separated into those that are clear and distinct and those that are confused and obscure. The former group consists of the ideas of extension, duration and movement. These geometrical ideas cannot be misconstrued or combined in a way that makes them false. For example, if the idea of a creature with the head of a giraffe, the body of a lion and tail of a beaver was constructed and the question asked if the creature had a large intestine, the answer would have to be invented. But, no matter how you combine or rearrange mathematical properties, the three angles of a triangle will still add up to 180 degrees and the largest side will always be opposite the largest angle. Thus, Descartes discovers that these truths have a nature or essence of themselves, completely independent of one's thoughts or opinions.
I find in myself innumerable ideas of things which, though they may not exist outside me, can't be said to be nothing. While I have some control over my thoughts of these things, I do not make the things up: they have their own real and immutable natures. Suppose, for example, that I have a mental image of a triangle. While it may be that no figure of this sort does exist or ever has existed outside my thought, the figure has a fixed nature (essence or form), immutable and eternal, which hasn't been produced by me and isn't dependent of my mind. (Descartes, Meditation V: On the Essence of Material Objects and More on God's Existence).
While thinking about the independence of these ideas of external objects, Descartes realizes that he is just as certain about God as he is about these mathematical ideas. He asserts that this is natural as the ideas of God are the only ideas that imply God's existence. He uses the example of a mountain and a valley. While one cannot picture a mountain without a valley, it's possible that these do not exist. However, the fact that one cannot conceive of God without existence inherently rules out the possibility of God's non-existence. Simply put, the argument is framed as follows:
This ontological argument actually originated in the work of St. Anselm, the medieval Scholastic philosopher and theologian. While Descartes had already claimed to have confirmed God's existence through previous arguments, this one allows him to put to rest any discontent he might have had with his "distinct and clear" criteria for truth. With a confirmed existence of God, all doubt that what one previously thought was real and not a dream can be removed. Having made this realization, Descartes asserts that without this sure knowledge in the existence of a supreme and perfect being, assurance of any truth is impossible.
Thus I plainly see that the certainty and truth of all my knowledge derives from one thing: my thought of the true God. Before I knew Him, I couldn't know anything else perfectly. But now I can plainly and certainly know innumerable things, not only about God and other mental beings, but also about the nature of physical objects, insofar as it is the subject-matter of pure mathematics. (Descartes, Meditation V: On the Essence of Material Objects and More on God's Existence).
In Meditation VI: Concerning the Existence of Material Things, and the Real Distinction between Mind and Body, Descartes addresses the potential existence of material outside of the self and God. First, he asserts that such objects can exist simply because God is able to make them.
Insofar as they are the subject of pure mathematics, I now know at least that they can exist, because I grasp them clearly and distinctly. For God can undoubtedly make whatever I can grasp in this way, and I never judge that something is impossible for Him to make unless there would be a contradiction in my grasping the thing distinctly. (Descartes, Meditation VI: On the Existence of Material Objects from Body).
Knowing that the existence of such objects is possible, Descartes then turns to the prevalence of mental images as proof. To do this, he draws a distinction between imagination and understanding, the former being something that is seen like a mental photograph and the latter being something that is understood but not pictured. He uses an example of this to clarify:
When I have a mental image of a triangle, for example, I don't just understand that it is a figure bounded by three lines; I also "look at" the lines as though they were present to my mind's eye. And this is what I call having a mental image. When I want to think of a chiliagon, I understand that it is a figure with a thousand sides as well as I understand that a triangle is a figure with three, but I can't imagine its sides or "look" at them as though they were present. (Descartes, Meditation VI: On the Existence of Material Objects and the Real Distinction of Mind from Body).
Descartes has still not given proof that such external objects exist, however, only shown that their existence could conveniently explain this mental process. To obtain this proof, he first reviews his premises for the Meditations - that the senses cannot be trusted and what he is taught "by nature" does not have much credence. However, he views these arguments within a new context; after writing Meditation I, he has proved the existence of himself and of a perfect God. Thus, Descartes jumps quickly to proofs of the division between the body and mind and that material things exist:
Proof for the body being distinct from the mind
However, this has been criticized as just because God can create a mind and body independently of each other (2), it does not necessarily follow that he has (7).
Proof of the reality of external material things
After using these two arguments to dispel solipsism and skepticism, Descartes seems to have succeeded in defining reality as being in three parts: God (infinite), minds, and material things (both finite). He closes by addressing other details about reality that some could see as inconsistencies, such as senses in amputated limbs, dropsy and dreams.
Descartes submitted his manuscript to several philosophers, theologians and a logician before publishing the Meditations. Their objections and his replies (many of which are quite extensive) were included along the first publication of the Meditations. In the Preface to the Meditations, Descartes writes: “I…ask my readers not to pass judgment on the Meditations until they have been kind enough to read through all these objections and my replies to them.” Thus, this dialogue could be seen as an integral part of Descartes' views expressed in the Meditations.
The seven objectors were, in order (of the sets as they were published): The Dutch theologian Johannes Caterus (Johan de Kater); various "theologians and philosophers" gathered by Descartes' friend and principal correspondent, Friar Marin Mersenne; the English philosopher Thomas Hobbes; the theologian and logician Antoine Arnauld; the philosopher Pierre Gassendi; another miscellany gathered by Mersenne; and the Jesuit Pierre Bourdin.
They make many objections to Descartes’ arguments and method. Some of the objections show that the objector has misunderstood the text. Descartes’ response to these is often dismissive and curt (e.g., in response to Hobbes, “I cannot possibly satisfy those who prefer to attribute a different sense to my words than the one I intended”). Other objections are more powerful, and in some cases it is controversial whether Descartes responds to them successfully.
Some of the most powerful objections include the following:
Objections to proof(s) of God’s existence:
A. We have no (clear) idea of an infinite Being (1st, 2nd, and 5th objections).
B. From the fact that I can think of a perfect being, it doesn’t follow that the perfect being exists (1st, 2nd, and 5th).
C. We could get the idea of God without God’s causing the idea (2nd, 3rd).
D. Nothing can cause itself to exist (4th), so God can’t cause himself to exist.
(Thus, without demonstrable causation (D), this proof cannot account for anything to exist, including itself.)
Objections to the epistemology:
A. How can we be sure that what we think is a clear and distinct perception really is clear and distinct (3rd, 5th)?
B. Circle objection 1: if we aren’t certain that judgments based on clear and distinct ideas are true before we prove God’s existence, then we can’t be certain that we are a thinking thing (2nd). Circle objection 2: if we aren’t certain that clear and distinct ideas are true before we prove God’s existence, then we can’t be certain that God exists, since we use clear and distinct ideas to prove God’s existence (4th).
C. Contrary to what Descartes argues, we are certain that bodies exist/that perception coincides with reality (5th, 6th).
Objections to philosophy of mind:
A. Ideas are always imagistic (3rd), so we have no idea of thinking substance (non-image idea).
B. We can’t conclude that the mind (thinking thing) is not also a corporeal thing, unless we know that we know everything about the mind. But we don’t know that we know everything about the mind. So we don’t know that the mind isn’t corporeal. (4th, 5th, 7th).