4.2.1 Primitive notions and the union
Descartes’s most extensive treatment of the union is in his correspondence with Elisabeth. Elisabeth’s stated motivation for writing to Descartes in the first place is to raise the problem of mind–body interaction (Bohemia and Descartes 2007: 91; AT iii: 661). In his first reply, Descartes addresses the problem in terms of primitive notions, of which three in particular are relevant: thought, extension, and union.
First I consider that there are in us certain primitive notions which are as it were the patterns on the basis of which we form all our other conceptions. There are very few such notions. First, there are the most general – those of being, number, duration, etc. – which apply to everything we can conceive. Then, as regards body in particular, we have only the notion of extension, which entails the notions of shape and motion; and as regards the soul on its own, we have only the notion of thought, which includes the perceptions of the intellect and the inclinations of the will. Lastly, as regards the soul and the body together, we have only the notion of their union, on which depends our notion of the soul’s power to move the body, and the body’s power to act on the soul and cause its sensations and passions
(CSMK: 218; AT iii: 665). That mind and body should be primitive notions is something we would expect. Descartes’s standard ontology is dualist, and everything in the material world is a modification of extension, while everything in the mind is a modification of thought. Necessarily, then, when we conceive of something material, we conceive of it through extension, and when we conceive of something mental, we conceive of it through
thought.4 So everything material comes down to matter itself, and everything mental to
mind itself. Since Descartes’s (standard) ontology contains nothing but thought and extension, our only options for conceiving of thought and extension are thought and extension themselves. And because substances can depend only on themselves5,
extension can tell us nothing about thought, and thought nothing about extension. So we cannot conceive of the one through the other, and thought and extension must be primitive.
Treating the union as a primitive notion as well, though, seems counterintuitive (at least under the aegis of standard accounts of Descartes’s ontology). After all, the union is meant to be a union of mind and body. On the face of things, it would seem perfectly natural to take the union to be, if anything, a composite notion, conceived through both thought and extension. Given Descartes’s famous dualism, given his famous ontological and explanatory parsimony, and given that the union is precisely a union of his two fundamental substances, we would reasonably expect it to be conceived through those two substances. Elisabeth too expects an explanation of the union in terms of thought and extension. This is presumably why the problem gets posed as a problem of mind–body interaction, rather than a problem of the union itself.
So, it would be consistent with his wider commitments for Descartes to characterise the union as a composite notion, but he makes it a primitive notion instead. Why this ultimately has to be his position is fairly straightforward. If extension can tell us nothing about thought, and thought can tell us nothing about extension, then neither thought nor extension can tell us anything about their union. This is because the union has properties that are present in neither the mind nor the body taken by themselves.6
So whatever we want to know about the union is not going to be conceivable through the notions of either thought or extension. And it cannot be conceivable though the notions of both thought and extension simultaneously either, just because thought and extension are necessarily conceptually isolated from each other: the notion of both thought and extension simultaneously is not covered by the individual notions of
4 See Nolan (1997: 130).
5 And, in the case of created substances, God (Principles 1/52–2).
6 On properties specific to the union, see (Simmons 2011: 9–10) and (Brown 2014: 248), who writes, ‘the
special subject of these irreducible modes is not one that Descartes can draw from his official ontology of basic substances, and hence he needs to conceive of the union as sui generis’.
thought and extension.7 Put another way, to appeal to both thought and extension
simultaneously is just to restate the problem of the union itself.
Necessarily, then, the union needs a notion of its own. Neither thought nor extension is going to do the job. And, because the other primitive notions (‘being, number, duration, etc.’) that Descartes mentions ‘apply to everything we can conceive’, they are not going to pick out anything specific to the union. So the only means we have of conceiving of the soul and the body together (or of both thought and extension simultaneously) is the notion of their union itself. And it is on this notion that Descartes claims our conception of mind–body interaction depends. Crucially, and against initial intuitions, our conception of mind–body interaction does not depend at all on on our notions of mind and body. This is in no way a trivial result: it means that thought and extension, which are supposed to be the fundamental elements of Descartes’s philosophy, can tell tell us nothing at all about the union.
This is a problem for Descartes’s system, specifically for his dualism and his reductionism. The world is supposed to consist of nothing but thinking substance and extended substance (and God), and everything within in it is supposed to be epistemically and ontologically reducible to thought or extension. But there is something in the world that is neither a thinking substance nor an extended substance, and that is not reducible to either. This is not just a matter of epistemic uncertainty. Descartes’s claim is explicitly not that he simply does not yet have a good explanation of the union in terms of thought or extension. His claim is there can be no explanation of the union in terms of thought or extension, for just the reasons covered above. The union requires a primitive notion of its own.
So, Descartes is explicit that the union exists and can only be conceived through a primitive notion of its own. The outcome of this is that, if Descartes’s philosophy is, fundamentally, the dualist system we take it to be, then it contains something it necessarily cannot explain: if the dualist system is Descartes’s philosophy, then the union is necessarily indefinable within Descartes’s philosophy. It seems that we have to conclude either that Descartes’s system is traditionally dualist but fails in a highly non- trivial way, or that it is (in one way or another) not dualist. My interest here is in the
7 This is evidenced by the existence of properties particular to the union. As Simmons puts it, ‘Descartes
himself insists that a real human being is nothing like an angel in a machine (or and angel in an animal). He takes the presence of sensations, appetites, and passions to be decisive evidence that the human being consists in some kind of a union of mind and body, and not in a mere aggregation of them’ (Simmons manuscript: 10–1; see also Simmons manuscript: 18).
second option.
4.2.2 The notion of union is prior to the notions of mind and body
If my approach is to deny dualism in some way, then the obvious, and established (if still controversial), route to take would be trialism. That is not the route I am going to take, for both metaphysical and epistemological reasons. Metaphysically, trialism assumes that the ontological categories that apply to the dualist system (namely, substance) can also be applied to the union. It is not obvious that they can (see (Brown 2014: 255)).8 Epistemologically, trialism treats the union9 as a primitive notion on a par
with the notions of thought and extension; my position is that the union has priority over thought and extension. I take it that the notions of thought and extension are, in a certain sense, secondary to the notion of union. This is a tricky route to take, for at least two reasons. First, the textual evidence makes it seem uncomfortably clear that, if Descartes is serious about his doctrine of primitive notions, he means each to be incompatible and incomparable with any other, thanks to their conceptual isolation. Hoping to establish priority between incompatibles seems quixotic. Second, giving the notion of the union priority over the notions of thought and extension seems, if anything, more incongruous with Descartes’s system as we know it than does allowing an inexplicable union into a dualist system (at least initially).
I’ll leave the second problem for §§4.3–4.5 (briefly, it’s not as incongruous as it sounds, and it neatly solves some problems that are otherwise fairly intractable). In the current section, I am going to show that, for humans, the notion of the union must be epistemically prior to the notions of thought and extension. Then (in §4.3, we’ll solve the first problem by showing that the priority comes not from relations between the notions themselves (of which there cannot be any), but from an equivocation between domains of conceivability that Descartes undergoes in his reply to Elisabeth. This is because, although the union is not conceivable in terms of the notions of thought and/ or extension, thought and extension are both perfectly conceivable in terms of the union. And it is not just that thought and extension are in principle conceivable in terms of the union; it is that Descartes does in practice derive thought and extension from
8 I agree with Hoffman that ‘it seems implausible to read [Descartes] as suggesting [. . .] that the union of
mind and body should be considered to be an attribute, that is, something constituting the nature or essence of a substance’ but disagree that Descartes’s treatment of the union constitutes a hylomorphic account (2008: 392) – for the reasons set out in §§4.3 and 4.4, Descartes’s account of the union requires treatment in terms of a separate, subjective metaphysics.
the union (that derivation is notably represented in the structure of the Meditations). Indeed, if my reading is correct, for humans, the notions of thought and extension are necessarily derived from the union.10
When Descartes introduces the primitive notions in the letter to Elisabeth, he explains that ‘we go wrong if we try to explain one of these notions by another, for since they are primitive notions, each of them can be understood [entenduë] only through itself ’ (CSMK: 218; AT iii: 666). This works, for the reasons covered above, for thought and extension: the notion of thought is not going to be able to tell us anything about extension, and vice versa. It also works for trying to understand the union through the notions of thought and/or extension: neither thought nor extension, nor any combination thereof, will be able to tell us anything about the union, and this is exactly our original problem. But does it also work for understanding thought and extension through the notion of the union? That seems less convincing. If mind and body are two sides of the union, which they are, and if we have a primitive notion of the union, which we do, then, in principle, what prevents our being able to understand both mind and body through the union? Nothing, as far as I can see. Conversely, if we had only a primitive notion of mind and a primitive notion of body, then we would never be able to understand the union through them (again, for all the reasons above). There are at least three ways to argue this, and those arguments follow in the next few sections. The first two are my major arguments; the third is somewhat supplementary (but has far- reaching implications).
4.2.2.1 Argument from containment
In his cosmological argument for the existence of God, Descartes relies on the doctrine that a cause (or dependency) must contain at least as much as its effect (or dependent):
it is manifest by the natural light that there must be at least as much in the efficient and total cause as in the effect of that cause. For where, I ask, could the effect get its reality from, if not from the cause? And how could the cause give it to the effect 10 The derivation involved is not a logical derivation: it is not the derivation of epistemic justification from
well-founded grounds. It is a causal derivation of the notion itself, rather than of its justification (Cf. Demos (1934) on ‘biological derivation’ – although Demos still conflates the justification of a notion with the notion itself). This is much like the derivation of a metal from its ore: in a world where iron is only found naturally as iron oxide, pure iron can only be derived from its oxide; this is separate from the justification of iron as an element. Similarly, in the world of the union (i.e. the subjective world of any human), the notions of thought and extension can only be derived from the notion of union; and this is separate from their intellectual justification as independent substances.
unless it possessed it? It follows from this both that something cannot arise from nothing, and also that what is more perfect – that is, contains in itself more reality – cannot arise from what is less perfect. [. . .] A stone, for example, which previously did not exist, cannot begin to exist unless it is produced by something which contains, either formally or eminently everything to be found in the stone; similarly, heat cannot be produced in an object which was not previously hot, except by something of at least the same order <degree or kind>11 of perfection as heat, and so
on.
(Meditations 2; CSM ii: 28; AT vii: 40–1). There has to be some source for the effect already contained within its cause. This is why, as Descartes explains it here, something cannot come from nothing. In Descartes’s example, a stone can only be produced by something that already contains stone, or that contains the components of stone. This containment can be formal, in which case the cause literally contains what is in the effect. Or it can be eminent, in which case the cause contains what is in the effect in some higher form (which explains how God could have created a world that includes divisible matter while being indivisible himself12). So, y can be derived from x just in case y contains nothing that x
does not. Consequently, if y contains something that x does not, then y cannot have been derived from x.
Applying this doctrine to the primitive notions, we see that the notion of the union contains more than the notion of thought does: the union necessarily also involves body. And since the union also necessarily involves mind, the notion of the union contains more than the notion of extension does. So the notion of the union cannot be derived from the notion of thought and cannot be derived from the notion of extension (this, of course, is another version of the arguments covered above). But, crucially, that does not seem to be true of the converse. The union is a union of both thought and extension. With that in mind, is there anything in the notion of thought that is not already contained in the notion of the union? And is there anything in the notion of extension not already in that of the union? The answer, in both cases, seems to be no.
If I am right here, then the notions of both thought and extension are derivable from the notion of the union (and not vice versa). In itself, this does not mean that the
11 Insertions in angle brackets are included in CSM and are from the 1647 French translation of the
Meditations, which Descartes had approved.
notions of thought and extension are in fact derived from the notion of union, of course. The individual notions could still be derived independently of the union (presumably, from God; that is, as innate ideas bestowed on us by God). But they are nevertheless derivable from the union. It does not seem like a stretch to conclude that one-way derivability is a (weak) form of epistemic priority. And, if so, then the notion of the union is prior to the notions of both thought and extension.
4.2.2.2 Argument from the order of the Meditations
The basic structure of the Meditations is, broadly speaking, analysis followed by synthesis (AT vii: 155; Williams 1978: 33). The method of doubt is what prompts the analysis, stripping away the familiar world to leave us with only the indubitable truths. Our familiar world then gets built back up on top of these truths. The standard reading of the Meditations privileges the indubitable truths. They are, explicitly, meant to be the foundations of Descartes’s entire philosophy (on the reading given here, of course, they are only the foundations of a restricted part of his philosophy): Descartes opens Meditation One by asserting the need ‘to demolish everything completely and start again right from the foundations if I wanted to establish anything at all in the sciences that was stable and likely to last’ (CSM ii: 12; AT vii: 17). So, given the truths of the cogito and the existence of God, Descartes is supposed to be able to derive true knowledge of the world. The cogito itself shows that there is thought, while the existence of God ensures that there is extension.
What concerns us here, however, are the prerequisites for the analysis that leads to the indubitable truths. We know that we need the cogito in order to prove the existence of God, because each of Descartes’s proofs relies on an idea of God that inheres in some thinking subject.13 So the cogito is a prerequisite for the proof of God’s existence. And
so the cogito is (logically) prior to the proof of God’s existence. Given that, we can put the proof of God’s existence to one side and focus on the cogito. What we want to know are the conditions required for deriving the ‘I am, I exist’ that is supposed to hold up the whole edifice. On this face of it, this might seem like a strange thing to look for. The entire point of the cogito is that it has no dependencies beyond itself, precisely because it is its own grounds – that is what makes it indubitable. If that’s so, it should have no prerequisites.
13 Even the argument from existence as a perfection relies first on my conceiving of God as perfect (AT vii:
However, in the Second Replies, Descartes makes very explicit that the order of the Meditations is in no way accidental:
The order consists simply in this. The items which are put forward first must be known entirely without the aid of what comes later; and the remaining items must be arranged in such a way that their demonstration depends solely on what has gone