Fifth Meditation

The Structure of Meditation 5

  1. Essence of matter is extension (7:63, 71)
  2. Innate ideas of essences (7:63–5)
  3. Ontological argument (7:65–8)
  4. Primacy of clear and distinct perception (7:68–9)
  5. Knowledge of God needed to banish doubt (7:69–71)

Descartes begins by asking whether “any certainty can be achieved regarding material objects” (7:63). This leads him first to make a claim about the essence of matter.

The Essence of Matter

The essence of matter is “continuous quantity” or extension

Quantity, for example, or ‘continuous’ quantity as the philosophers commonly call it, is something I distinctly imagine. That is, I distinctly imagine the extension of the quantity (or rather of the thing which is quantified) in length, breadth and depth. I also enumerate various parts of the thing, and to these parts I assign various sizes, shapes, positions and local motions; and to the motions I assign various durations. (7:63)

One innovation here is that Descartes argues that we can know the essence of a thing whether or not we know that it exists. In this sense knowledge of essence is independent of knowledge of existence. This is in contrast to the Aristotelian conception according to which knowledge of essence is something ‘abstracted’ from our experience of objects in the world.

Essence as Primary Attribute

What is it to say that the essence or primary attribute of matter is extension? In the Principles, Descartes explains that each substance has a “principal attribute” or “property” that “constitutes its nature and essence, and to which all its other properties are referred” (8A:25). This means that all of the properties of a thing—including all its modes—are to be “referred” to some primary property, without which that thing would not be what it is. In the case of body (i.e. matter), the primary attribute or “essence” is extension.

Descartes seems to be making two claims here. The first concerns the intelligible structure of a thing. In reasoning about or understanding what a thing is, Descartes claims, we must be able to make connections between the various qualities attributed to a thing. If we cannot then we will not be able to understand what the thing is and why it is that way. In the case of body, Descartes is claiming that our understanding of any body requires thinking of it as first and foremost, an extended thing. All other properties attributed to a body must therefore be understood in relation to its being extended, and ultimately just as ways of its being extended.

Descartes is thus making, aside from the above claim about intelligibility, a metaphysical claim as well—viz. that the property of being extended is the most metaphysically fundamental property a material substance can have, and is the property upon which all of its other properties rely.

Essence Generalized

After claiming to have articulated the essence of body, Descartes goes on to make a series of more general claims about how one might come to knowledge of the essence of a thing independently of any issue of its existence. We might come to have knowledge of the “true and immutable nature” (7:64) of a thing by reflection on our idea of it. The content of this idea need not have come from anything outside the subject—it could be innate. Moreover, its content is “not invented by me [the meditator] or dependent on my mind” (7:45). The mark of this is somewhat psychological. Descartes notes that with respect to such ideas (e.g. geometric ideas) they seem not invented but rather discovered. They are truths which the mind recognizes whether it wants to or not (7:64). This point, that one can have knowledge of the essence of a thing just by contemplating a clear and distinct idea of it, and that such contemplation can give one knowledge of it is then put to work by Descartes with respect to the idea of God and of God’s essence.

Knowledge of Essence is Innate

Descartes considers the objects of knowledge in mathematics to be “true and immuatable natures” that are “discovered” in some sense rather than invented, imagined, or received through the senses.

I find within me countless ideas of certain things, that, even if perhaps they do not exist anywhere outside me, still cannot be said to be nothing. And although, in a sense, I think them at will, nevertheless they are not something I have fabricated; rather they have their own true and immutable natures. For example, when I imagine a triangle, even if perhaps no such figure exists outside my thought anywhere in the world and never has, the triangle still has a certain determinate nature, essence, or form which is unchangeable and eternal, which I did not fabricate, and which does not depend on my mind. This is evident from the fact that various properties can be demonstrated regarding this triangle…These are properties I now clearly acknowledge, whether I want to or not, even if I previously had given them no thought whatever when I imagined the triangle. (7:64)

Note Descartes’s emphasis, in the above passage, on the way in which mathematical ideas are not “fabricated” but rather “discovered”. This claim is based partly on the fact that the experience (what we might call the “phenomenology”) of thinking through mathematical ideas is an experience akin to discovery rather than invention. Moreover, mathematical ideas, or their objects, are not subject to our whim or control in the way that invented fictions are. We cannot, for example, just decide that 2+2=5 or that the interior angles of a triangle sum to 190°.

This knowledge of the natures of things is not acquired on the basis of sensory ideas or invented fictions. Instead it is achieved purely via exercise of the intellect (don’t let Descartes’s use of “perceive” fool you – he construes “perception” as a kind of catch-all term for intellectual scrutiny or attention), but in a manner that is a discovery of something rather than its invention.

Descartes is thus adverting to a doctrine of innate ideas that he first mentions in the Third Meditation. These ideas are discovered in the mind simply in the activity of thinking and not via sense experience or invention.

Four Features of Innate Ideas

Descartes describes four characteristics of the manner in which innate ideas manifest and are significant in thought.

Not only are all these things very well known and transparent to me when regarded in this general way, but in addition there are countless particular features regarding shape, number, motion and so on, which I perceive when I give them my attention. And the truth of these matters is so open and so much in harmony with my nature, that on first discovering them it seems that I am not so much learning something new as remembering what I knew before; or it seems like noticing for the first time things which were long present within me although I had never turned my mental gaze on them before. (7:63–4)

We can break down this discussion of innate ideas more simply. They have four features:

  1. Transparency
  2. Fecundity
  3. Non-empirical/non-fabricated
  4. Harmony

Innate ideas are transparent in the sense of being available for conscious attention and scrutiny. They are fecund in the sense of being epistemically significant in generating a variety of systematically connected ideas. For example, the idea of extension is basic to all of our ideas of motion, shape, size, etc. As we’ve already discussed, innate ideas are non-empircal and non-fabricated in the sense of not coming from the senses, but also not being a kind of fiction of the imagination either – i.e. they are discovered. Finally innate ideas are harmonious in the sense of following from the natural activity of the intellect.

The Ontological Argument

We’ve looked at Descartes’s discussion of our ideas of essences, but his discussion of essence and discovery also leads him to provide a version of a classic (and somewhat infamous) argument for the existence of God – the “ontological” argument, first made by St. Anselm in the Proslogion of 1077-78 (11th century). Here we’ll look at the structure of the argument, its significance, and some objections to it.

Structure of the Argument

  1. Statement of the ontological argument (7:65)
  2. Objection 1: existence is separable from essence (7:66)
  3. Objection 2: existence in thought is different from real existence (7:66)
  4. Objection 3: the necessity of God’s existence is only hypothetical (7:67)

The Argument

The ontological argument differs from Descartes’s previous proofs in that it purports to prove God’s existence simply from an innate and clear and distinct idea of God’s essence. So this isn’t a proof that relies on the cause of the idea, or on the finitude or preservation of the subject.

if the mere fact that I can produce from my thought the idea of something entails that everything which I clearly and distinctly perceive to belong to that thing really does belong to it, is not this a possible basis for another argument to prove the existence of God? Certainly, the idea of God, or a supremely perfect being, is one which I find within me just as surely as the idea of any shape or number, And my understanding that it belongs to his nature that he always exists) is no less clear and distinct than is the case when I prove of any shape or number that some property belongs to its nature. Hence, even if it turned out that not everything on which I have meditated in these past days is true, I ought still to regard the existence of God as having at least the same level certainty as I have hitherto attributed to the truths of mathematics. (7:65)

The proof differs from previous versions of the ontological argument, in that it does not depend on an arbitrary definition of God but rather an innate idea whose content is clearly and distinctly perceived. Thus, just as one can come to know basic geometrical truths by reflecting on the content of geometric ideas, Descartes thinks one also comes to know that God exists, just by reflection on the content of one’s idea of God.

Three Objections

Existence and Essence

The first objection is that we readily distinguish between the essence of a thing, what it is for that thing to be the kind of thing it is, and the existence of a thing. A ready example of this can be seen in geometry. Geometrical figures, as described by, e.g. Euclid, have essences. That is, they have definite characteristics that categorize them as the things they are (triangles have three sides and angles that sum to 180˚, quadrilateral figures have four sides and angles that sum to 360˚, etc.). However, it would be wrong to say that, for these figures, their essence is inseperable from their existence. For a particular geometric figure, we can distinguish what characteristics it must necessarily have were it to exist even when conceding that the figure may not actually exist. If we can make this distinction in the case of geometric figures, then why not with God? Descartes puts the objection this way:

Since I have been accustomed to distinguish between existence and essence in everything else, I find it easy to persuade myself that existence can also be separated from the essence of God, and hence that God can be thought of as not existing (7:66)

Descartes then replies that careful consideration of the content of the idea of God shows us that God’s essence is inseparable from its existence.

when I concentrate more carefully, it is quite evident that existence can no more be separated from the essence of God than the fact that its three angles equal two right angles can be separated from the essence of a triangle, or than the idea of a mountain can be separated from the idea of a valley. Hence it is just as much of a contradiction to think of God (that is, a supremely perfect being) lacking existence (that is, lacking a perfection), as it is to think of a mountain without a valley (7:66)

Here we get a clarification of Descartes’s view. The reason why it would be self-contradictory to think of God as lacking existence is because existence, according to Descartes, is a perfection, and God essentially (i.e. as part of God’s essence) has all perfections, so God must exist.

Real or Fictitious?

The next objection worries about how we can be sure that the content of our ideas matches reality.

even granted that I cannot think of God except as existing, just as I cannot think of a mountain without a valley, it certainly does not follow from the fact that I think of a mountain with a valley that there is any mountain in the world; and similarly, it does nor seem to follow from the fact that I think of God as existing that he does exist. For my thought does not impose any necessity on things; and just as I may imagine a winged horse even though no horse has wings, so I may be able to attach existence to God even though no God exists. (7:66)

So the objection asks (i) whether it would follow simply from one’s thought that God exists that He exists, which (ii) seems fallacious given other examples of fictitious thought, such as thinking of a winged horse.

Descartes replies that this objection gets things the wrong way round.

there is a sophism concealed here [i.e. in the above argument]. From the fact that I cannot think of a mountain without a valley, it does not follow that a mountain and valley exist anywhere, but simply that a mountain and a valley, whether they exist or not, are mutually inseparable. But from the fact that I cannot think of God except as existing, it follows that existence is inseparable from God, and hence that he really exists. It is not that my thought makes it so, or imposes any necessity on any thing; on the contrary, it is the necessity of the thing itself, namely the existence of God, which determines my thinking in this respect. For I am not free to think of God without existence (that is, a supremely perfect being without a supreme perfection) as I am free to imagine a horse with or without wings. (7:66-7)

Descartes denies that his claim is that thinking makes it so—the necessity of God’s features constrain our thinking concerning them. Descartes also denies that the connection could be merely fictitious. If it were then the connection would be under the thinker’s control, in the way that thinking of a horse as winged (or not) is under the thinker’s control. Hence, Descartes assumes that thought of fictitious connections is always subject to the thinker’s will, while what is intrinsically connected will be inseperable in thought.

Hypothetical Necessity

Descartes then goes on to pose a third objection:

[Assuming that] while it is indeed necessary for me to suppose God exists, once I have made the supposition that he has all perfections (since existence is one of the perfections), nevertheless the original supposition was not necessary. Similarly, the objection would run, it is not necessary for me to think that all quadrilaterals can be inscribed in a circle; but given this supposition, it will be necessary for me to admit that a rhombus can be inscribed in a circle – which is patently false. (7:67)

In other words, if we assume that God has all perfections, and that existence is such a perfection, then Descartes’s conclusion follows. But why make these assumptions? What justifies them?

Descartes’s reply again draws on the distinction between the content of a fictitious idea, whose characteristics may be separated at will, and the content of the idea of God, which necessarily posits God’s possession of all perfections, including existence.

Now admittedly, it is not necessary that I ever light upon any thought of God; but whenever I do choose to think of the first and supreme being, and bring forth the idea of God from the treasure house of my mind as it were, it is necessary that I attribute all perfections to him, even if I do not at that time enumerate them or attend to them individually. And this necessity plainly guarantees that, when I later realize that existence is a perfection, I am correct in inferring that the first and supreme being exists. In the same way, it is not necessary for me ever to imagine a triangle; but whenever I do wish to consider a rectilinear figure having just three angles, it is necessary that I attribute to it the properties which license the inference that its three angles equal no more than two right angles, even if I do not notice this at the time. By contrast, when I examine what figures can be inscribed in a circle, it is in no way necessary for me to think that this class includes all quadrilaterals. Indeed, I cannot even imagine this, so long as I an willing to admit only what I clearly and distinctly understand. So there is a great difference between this kind of false supposition and the true ideas which are innate in me, of which the first and most important is the idea of God. (7:67-8)

So the idea of God includes the concept <existence>, in the just the same (necessary) way that the idea of a triangle includes <three sided>. We know that “This idea isn’t a fiction, a creature of my thought, but rather an image of a true and unchanging nature” because we have a clear and distinct perception of it.

Caterus’s Objection

Even if it is granted that a supremely perfect being carries the implication of existence in virtue of its very title, it still does not follow that the existence in question is anything actual in the real world; all that follows is that the concept of existence is inseparably linked to the concept of a supreme being. So you cannot infer that the existence of God is anything actual unless you supposes that the supreme being actually exists; for then it will actually contain all perfections, including the perfection of real existence. (7:99; CAM p. 136)

In other words, do we really know that such a being exists that corresponds to our concept? Descartes takes the objection to be a version of the second objection discussed above—viz., whether the concept of God is fictional, in the sense of being constructed out of other materials (e.g. our experience of finite beings from which we extrapolate). But Caterus seems to be objecting to the claim that the necessity to which we attach the concept <existence> to the concept <God> must track or mirror some real relation of God’s existence in reality. Caterus is thus not objecting to the claim Descartes makes concerning the connection of the two concepts <existence> and <God>. Instead he is objecting to the claim that this conceptual connection is a sufficient basis for making a claim about an extra-mental reality—viz. that God (the being) and existence (the property) really are so connected.

Caterus’s objection is especially pressing, given that for Descartes the idea of God is innate. The question is thus how an innate idea, an idea that does not originate from the external world, could nevertheless accurately reflect reality. This worry holds as much for geometrical figures, which determine the essential properties of all material beings, as it does for God.

To that extent that Descartes has resources to defend his version of the ontological argument, the defense hinges on his fundamental claim that clear and distinct ideas, despite their being innate, provide us with an adequate representation of reality. This would seem to point to the truth rule – the idea that clear and distinct ideas are true and sufficient for knowledge. Hence, we have to consider the justification for the truth rule, if there is any.

The Cartesian Circle

As was suggested in the discussion of the Third Meditation, the need for a proof of God hinges, at least in part, on the need for a certification of clear and distinct ideas as guaranteeing truth. At the end of the Fifth Meditation Descartes makes clear that such a proof is necessary if we are to achieve certainty of even the simplest things, such as basic mathematical truths.

Now, however, I have perceived that God exists, and at the same time I have understood that everything else depends on him, and that he is no deceiver; and I have drawn the conclusion that everything which I clearly and distinctly perceive is of necessity true. Accordingly, even if I am no longer attending to the arguments which led me to judge that this is true, as long as I remember that I clearly and distinctly perceived it, there are no counter-arguments which can be adduced to make me doubt it, but on the contrary I have true and certain knowledge of it. And I have knowledge not just of this matter, but of all matters which I remember ever having demonstrated, in geometry and so on…Thus I see plainly that the certainty and truth of all knowledge depends uniquely on my awareness of the true God, to such an extent that I was incapable of perfect knowledge about anything else until I became aware of him. (7:70-1)

In the Third Meditation Descartes argued that his clear and distinct idea of God grounded certainty of God’s existence. God’s existence and nature were then used to ground the truth rule. Arnauld, in the Fourth Objections points out that this reasoning is circular.

I have one further worry, namely how [Descartes] avoids reasoning in a circle when he says that we are sure that what we clearly and distinctly perceive is true only because God exists. But we can be sure that God exists only because we distinctly and clearly perceive this. Hence, before we can be sure that God exists we ought to be able to be sure that whatever we perceive clearly and evidently is true. (7:214; CSM p. 142)

Descartes’s reply relies on the distinction between knowledge, at a time, derived from one’s clear and distinct ideas, and knowledge at some later time based on the memory of such a derivation (7:246; CSM 142-3). Descartes argues that the proof of God relies only the on the clear and distinct idea of God, while the subject’s capacity to retain knowledge (but not the reliability of clear and distinct ideas themselves), such as through memory, relies on the the proof of God’s existence, and the fact that He is no deceiver (see, e.g., (Van Cleve 1979); (Frankfurt 2008)).

Is this a convincing means of getting out of the circle?


Frankfurt, Harry G. 2008. Demons, Dreamers, and Madmen: The Defense of Reason in Descartes’s Meditations. Princeton, NJ: Princeton University Press.

Van Cleve, James. 1979. “Foundationalism, Epistemic Principles, and the Cartesian Circle.” The Philosophical Review 88 (1):55–91.

Icon by Nun from The Noun Project. Website built with Org-mode, Hugo, and Netlify.