From now at

Cartesian Dualism and the Union of Mind and Body: A Synchronic Interpretation

Zuraya Monroy-Nasr

ABSTRACT: Cartesian dualism and the union of mind and body are often understood as conceptions that contradict each other. Diachronic interpretations maintain that Descartes was first a dualist (in the Meditations) and later on developed his stance on the union of mind and body (Passions). Some authors find here a problem without solution. Nevertheless, in the last two decades, some interpretations have been developed intending to give a positive solution to the difficult relation between Cartesian dualism and the union of mind and body. The problem that I find in most of them is that they try to show no incoherence between Descartes' dualism and his conception of the union and interaction by "weakening" or making more "flexible" the dualist doctrine. I develop a synchronic interpretation, based on textual evidence, in order to show that dualism and union appeared simultaneously in Descartes' works. Under this perspective, my claim is that Cartesian radical dualism and the union of mind and body can be coherently understood only because they belong to different domains of knowledge. Thought and matter are clear and distinct primitive notions that come from reason, whose role is laying the foundations for Cartesian metaphysics and physics, while the primitive notion of union is acquired by the senses and lacks clarity and distinction even while it serves the objective of founding Descartes' moral philosophy.

Rene Descartes is well known for his dualist conception. At the same time, Descartes recognized the intimate relation between the human mind and body. Several authors have understood this as a contradiction within Cartesian philosophy.

Truly, when Descartes argues in favor of dualism between the extended and the non-corporeal substances, he is completely radical about their separation. So, when he asserts the union between the human mind and body, some interpreters find that he presents a contradictory position. Others think that probably Descartes was not so radical in his dualism.

In order to build a different interpretation about the Cartesian dualism and the union of mind and body, I have established two categories. I call diachronic interpretations those that maintain that Descartes was first a dualist (i.e., in the Meditations), and later on developed his stance on the union of mind and body (i.e., in the Passions).

Against diachronic perspectives, I propose a synchronic interpretation under which I maintain that Cartesian dualism and the union of mind and body are simultaneously present all along Descartes works. (1) Through this category I try to accomplish my purpose in this paper, which is to show that there is coherence and intelligibility in Descartes conceptions of dualism and union.

Redefinition of the Problem under a Synchronic Interpretation

When Princess Elisabeth questioned Descartes on the possibility of interaction between heterogeneous substances [AT III 661]., he answered recognizing that through his works, he had not said much about the union of mind and body. In his letter [21-05-1643] Descartes justifies this saying he had been primarily focused in the demonstration of the distinction between mind and body.

Descartes himself recognized the uneven development of his doctrine on dualism and his doctrine on the union and interaction of mind and body. I think that, as a consequence of this unequal treatment of dualism and union, from Descartes days until now, there has been a large tendency to understand them as conceptions that developed successively. Gassendi and Elisabeth had diachronic interpretations, and nowadays many authors maintain similar views on Descartes doctrines on union and dualism.

I do not have enough space to discuss here any particular diachronic interpretation. Besides, it is widely accepted that the distinction between extended and non-extended substances was previously conceived by Descartes, and that it is the departing point to explain the union of mind and body and its interaction.

In effect, Cartesian dualism claims the independent existence of a non-corporeal realm and a physical realm. But, at the same time, through his works, whenever Descartes presents the distinction between thought and matter, he mentions the tight relation in the human beings between mind and body. This can be found in the Rules [AT X 415; CSM I 42], it is clearly stated in the Treatise on Man [AT XI 119-120; CSM I 99], and is fully developed in the Meditations.

In the Sixth Meditation, we can see that Descartes comes to the conclusion that my essence consists solely in the fact that I am a thinking thing, and immediately after affirms that he certainly has a body that is very closely joined to me [AT IX 62; CSM II 54].

In this passage the union is initially mentioned as a possibility, but right away, to anticipate says Descartes, it is stated with certainty. Here, Descartes tells us about the fact of the union, but he does not give any further explanations. Anyway, these are not necessary, because what follows in his argument is that, despite this union, there is no obstacle to affirm that ... I have a clear and distinct idea of myself, in so far as I am simply a thinking, non-extended thing; and on the other hand I have a distinct idea of body, in so far as this is simply an extended, non-thinking thing. Then, he finally concludes the argument saying that it is certain that I am really distinct from my body, and can exist without it [AT IX 62; CSM II 54].

Dualism and union are present in the same argument, but while the former is the main topic and Descartes center of attention, the latter is only mentioned as a fact. Now, the first step of my synchronic interpretation is to point out the simultaneous presence of dualism and union. But, of course this does not save Descartes from the accusation of having an incoherent conception about the substantial distinction and the union and interaction of mind and body.

The synchronic perspective allows us to redefine the problem of the relation dualism/union and propose the thesis that Descartes is building two different doctrines, with distinct objectives, simultaneously present but in a very different way. On the one hand, we know that one of the main roles of Cartesian dualism is to found metaphysically his physical science, and for this reason Descartes gave especial attention to dualism. On the other hand, it was not until his final works that he found necessary to say more about the union and interaction of mind and body. Anyway, what must be quite clear is that whenever Descartes argued in favor of the substantial distinction, he also mentioned the particular case of the union of mind and body in the human beings. So, instead of insisting in the possible contradictions between dualism and union, I prefer to follow a new direction and try to find the place of each of these doctrines in the Cartesian system.

Synchrony and Coherence

In a famous passage in the Sixth Meditation, Descartes denies that the mind is merely present in the body. For him, the mind is very closely joined and intermingled with the body. Furthermore, it is through sensations (i.e., pain, hunger, thirst), and not by an intellectual inspection, that we are aware of the needs of our body [AT IX 64; CSM II 56]. Here, we find that Descartes places our knowledge of the union of mind and body in a phenomenological level, (2) quite different from the epistemological level, in the domain of his metaphysics, where the doctrine of dualism is placed.

Due to his dualism, Descartes received many objections about his conception of the union of mind and body. He replied several of these, but the most detailed, patient and enthusiastic replies were those addressed to Princess Elisabeth, in 1643.

Descartes answer is supported by his doctrine on the primitive notions. Although he mentions several notions, for the problem we are interested on, the significant ones are: the notion of extension (which includes figure and movement), the notion of thought (including the conceptions of the intellect and the inclinations of the will), and the notion of the union of mind and body (on which depends the interaction that causes sensations and passions).

J. Cottingham calls our attention when he points out that, Commentators, it must be said, have expressed some irritation with this passage: how, it is asked, can a notion be called primitive if it is dependent on a union of two elements? A mule can hardly be called a primitive species if it comes from the union of a horse and an ass. (3)

For Cottingham, Descartes has perhaps not expressed himself too helpfully here. (4)

I disagree in this respect with this author, because in the very next paragraph, that Cottingham does not quote or mention, Descartes clearly expresses that each primitive notions can only be understood by itself. So, perhaps the irritation of commentators comes from misunderstanding Descartes argument, due to a diachronic interpretation.

Cottingham contributes towards a positive interpretation of the problematic relation between dualism and union, and develops his Cartesian trialism. Under this model, along with the official dualism he thinks that Descartes has a trialistic model which has the flexibility that dualism lacks. I will not discuss in detail Cottinghams arguments for trialism, although I have argued on this matter somewhere else. (5) Nevertheless, I find important to recognize his contribution to our understanding of Descartes phenomenology of sensation, which attaches to us qua embodied beings (6)

Cottinghams Cartesian trialism emerges from the difficulty to regard sensation and imagination as purely mental faculties, due to the fact that they involve the activity of a hybrid unit. Nevertheless, in my opinion trialism presents several problems.

Cottingham clearly observes that he is not conceiving the union as a new substance or a third ontological category. But, according to him, it reveals a modification in Descartes official dualistic doctrines (7). This suggests that trialism is a partial substitute of dualism, that allows Descartes to explain the modes or attributes that do not belong to the substantial distinction.

But if trialism is not an ontological doctrine, how can it substitute, even partially Descartes ontological dualism? It is not clear to me why Descartes categorization of primitive notions results in a more flexible model. In my opinion, what Descartes intends to show Elisabeth about the union of mind and body, is that it is a doctrine in another level and in a different line of reasoning than the one he followed to prove the real substantial distinction.

Based on Descartes primitive notions L. Bentez, as well as R.C. Richardson have developed interesting interpretations. Bentez argues that while thought and extension are the notions which found the Cartesian metaphysics and physics, the union of mind and body appears as the fundamental notion upon which Descartes builds his moral or practical philosophy. (8) So, as the notions of extension and thought are clear and distinct and we know them through reason, they belong to different epistemological levels. The notion of union arises from our sensations and requires the mediation of the body. Thus, it is not a clear and distinct notion. For this reasons, Bentez underlines that the notion of union makes possible the Cartesian approach to the knowledge of actions and passions of the soul.

Diachronic interpretations have disregarded the different epistemic levels and the independent dominions of these notions. They have also misunderstood Descartes line of reasoning on this matter. Richardson has developed an original interpretation, based on Descartes own texts, that intends to show there is no sound reason to think heterogeneity renders mind-body interaction incoherent. (9) Furthermore, he also explains why Descartes critics think such interaction to be incoherent.

Richardson points out that mind-body interaction appears incomprehensible, because it has been illicitly taken to be similar to causation in the physical realm. (10) So, Richardson maintains that Descartes conceives a different kind of causation, a non-mechanical one, for the interaction of mind and body. So, when we do not follow Descartes conception about the primitive notions which belong to their proper domain, we confusedly try to find an explanation for the union and interaction in the domain of the primitive notion of extension.

Descartes line of reasoning is different from what his critics have understood. And it was so from the beginning, when he conceived synchronically the separation of universal substances and the intermingled relation of the human mind and body. In his response to Elisabeth, Descartes tries to explain that, ... When we suppose that heaviness is a real quality of which all we know is the it has the power to move the body that possesses it towards the center of the earth, we find no difficulty in conceiving how it moves the body nor how it is united to it. We do not suppose that the production of this motion takes place by a real contact between two surfaces, because we experience in ourselves that we have a specific notion to conceive it. I think that we misuse this notion when we apply it to heaviness, which as I hope to show in my physics..., is not anything really distinct from body; but it was given us for the purpose of conceiving the manner in which the mind moves the body [21-05-1643].

Here, Descartes makes an analogy with the Scholastic conception of gravity, that he finds unacceptable due to his physical conception of the world. Nevertheless, it is useful for him to illustrate that: 1) each notion has its own dominion, and it is a mistake to apply the specific notion of union to the physical realm (including the mechanical causation) and 2) we are capable of conceiving two heterogeneous entities united and interacting, and without supposing any physical relation between them.

Kenny reproves Descartes response to Elisabeth saying that her question was not whether body and soul were united, but how; and the inconceivability of this is not lessened by being compared to another inconceivable. (11) Following Descartes argument and Richardsons original interpretation, I believe Descartes did understand Elisabeths question and tried to answer it under his own perspective.

In effect, Descartes did not say how the mind and body were united. But he replies that its explanation does not obey the mechanical causation that rules the body-body interaction. The example of gravity is directly intended to show how we conceive a non-mechanical causation. In other words, Descartes wants Elisabeth to realize that she has already used the notion of union, maintaining that it has been applied in the wrong dominion. The Scholastic theory of gravity may be inconceivable for Kenny, but for Descartes it is perfectly conceivable, although he thinks it is completely incorrect.

Descartes letter to Elisabeth has also received an original interpretation from Garber. I cannot develop here his arguments, but I briefly want to mention that according to him Descartes sees the Scholastic notion of gravity as a projection of an innate conception onto the natural world. (12) But what Garber finally questions of Descartes doctrine of primitive notions, is the idea that the body-body interaction can be fully intelligible under the primitive notion of extension. (13) Then, after a peculiar interpretation of Cartesian physics and how God acts on the world, Garber defends the intelligibility of the mind-body interaction and maintains it is the paradigm of all causal explanation. (14)


In the last two decades, several new interpretations have been developed against the critics to the intelligibility and coherence of the Cartesian doctrines of dualism and union. A point of coincidence has been recognizing the role of the Cartesian primitive notions. (15) Nevertheless, the relation between this notions has been understood in different ways.

Cottingham and Garber do not recognize the importance of the irreducibility of primitive notions. This, altogether with the absence of a synchronic view on dualism and union, leads them to weaken Cartesian dualism in order to develop their own interpretations. They do not find that Descartes own arguments can defend the coherence and intelligibility of his doctrines. Thus, they elaborate proposals as trialism (that is not an ontological doctrine as dualism) or as what Descartes should have told Elisabeth (although he never did).

Under a synchronic interpretation and with Descartes doctrine of primitive notions as well as their mutual independence, it is possible to achieve a coherent understanding of Cartesian dualism and the mind and body union. Both doctrines coexist, and each one corresponds to its proper dominion. Nonetheless, there is still the question of what is the non-mechanical causation. We need to find out about this kind of causation. I strongly belief that on this problem also, as Richardson and Bentez have shown concerning dualism and union, Descartes own arguments and conceptions can provide an effective reply to his past and present critics and interpreters. (16)


(1) The editions of Descartes works used here are: F. Alqui [A](selection, presentations and notes) 1963-1973: Descartes, Oeuvres Philosophiques (Paris: Garnier), following the canonic notation from Adam and Tannery [AT]; J. Cottingham, R. Stoothoff and D. Murdoch [CSM] 1985: The Philosophical Writings of Descartes (New York: Cambridge University Press);

(2) A. Kenny (ed. and trans.) 1970: Descartes: Philosophical Letters (Oxford: Clarendon Press).

(3) I am using the term phenomenology following the conception of J. Cottingham on the Cartesian phenomenology of sensation [cf. 1986: Descartes (Oxford: Basil Blackwell) p. 126].

(4) Cottingham 1985: Cartesian Trialism, Mind, p. 224.

(5) Ibid.

(6) See Z. Monroy-Nasr 1996: Cartesian Dualism: A Limited Vision or an Inevitable Conception, unpublished; 1997: De las Meditaciones a las Pasiones de R. Descartes. Distincin e Interaccin Substancial (Mexico: Doctoral Thesis FFyL-UNAM). Cf. Ibid., p. 223.

(7) Ibid., p. 218.

(8) L. Bentez 1993a: Reflexiones en torno al Interaccionismo Cartesiano, in L. Bentez and J.A. Robles, eds., El Problema de la Relacin Mente-Cuerpo (Mexico: IIF-UNAM) p. 32. R.C. Richardson 1982: "The 'Scandal' of Cartesian Interactionism," Mind, 91, p. 22.

(9) Cf. Ibid.

(10) A. Kenny 1968: Descartes: A Study of the Philosophy (Nueva York: Random House) p. 224.

(11) D. Garber 1983: "Understanding Interaction: what Descartes should have told Elisabeth," Southern Journal of Philosophy, 21, p. 21.

(12) Ibid., p. 27.

(13) Ibid., p. 29.

(14) Cf. Richardson, Op. Cit.; Garber, Op. Cit. and 1992:

(15) Descartes Metaphysical Physics (Chicago: The University of Chicago Press); Cottingham, Op, Cit.; Bentez, Op. Cit. and 1993b: El Interaccionismo Cartesiano y el Problema de la Glndula Pineal, in L. Bentez, ed., Homenaje a Descartes (Mexico: FFyL-UNAM); Madanes 1993: Abandonamos la Partida? Consideraciones sobre el Problema de la Relacin Mente-Cuerpo, in Bentez 1993a, Op. Cit.

(16) I am working on this subject, especially on the Cartesian semantics where I think we can find the arguments that point to an answer to this problem.