The solution of substance monist property dualism – or just ‘property dualism’, more conveniently – begins with the recognition that the brain is the seat of all mental occurrences. The latter must come to an absolute, impassable end when the former ceases to be. But this suggests that the physical entity of the brain, and the human body as a whole, is a bearer of mental properties, which cannot themselves be reduced to sheer materiality or equated with physical components. They are lodged in the body and inextricable from it: hence they belong to the exact same substance. They are non-physical properties of the body, the sum of which makes up the mind.20 Its signal marker is what Jacquette and other philosophers call ‘intentionality’. A thought is always about something. It points to an intended object, be it the daughter I long for, the food I crave, the argument I develop, the God I doubt, the storm I expect, the stomach pain that troubles me or the fascistisation of society that frightens me. In this context, ‘intentionality’ refers to an abstract relation between a mental state and an object, a link by which the former is directed towards the latter. It is an aspect of the thought itself – it is not this or that capillary or cortex that is about something; considered as a purely material entity, the brain is not turned towards a daughter or a dinner. It gives rise to the mental property of intentional thought, which is distinct from any physical property of the brain and inexpressible in the language pertinent to that underlying level. No one has yet explained how one could possibly scan the brain and pick out the neurochemical state that is about Donald Trump and not about Daenerys Targaryen.21
Moreover, when I think about Daenerys Targaryen and ponder her next move in the campaign for seizing Westeros, my thought is about a person who does not exist. Since she is a fictional figure, she cannot be physically connected to the material objects that make up my brain. Here it will not do to say that I am really thinking about the book by George R. R. Martin or the HBO series, since my thought concerns none of these things, but precisely Targaryen herself and her next tactical manoeuvre. I can think of many other things that do not exist in the here and now, inter alia a world that is six degrees warmer. This ability to engage with things that do not (yet) exist – something the brain and nervous system could never do, considered strictly as such – establishes a peculiar orientation towards the future, an openness to various options, the art of formulating a goal, faculties such as imagination and creativity and cunning. It follows that ‘the mind is a new category of entity in the material world.’22 Property dualists like Jacquette are adamant that there is nothing miraculous about this appearance – after all, science teaches us that life, with its amazing properties, evolved spontaneously once matter had organised itself into sufficiently complex patterns.23 So why should not life at a certain stage of its evolution be able to develop the wonder of the mind? Intentionality is an emergent property that cannot be reduced to the bedrock on which it supervenes, and cannot exist without it. All thought is actualised by events in the brain, and all thought has at least one property the matter of the brain cannot have sensu strictu.24
Property dualism, then, admits of only one substance – matter – but considers the human body a species of that substance in possession of uniquely mental properties. The beauty of this solution is that it avoids the Cartesian impotence in the face of the causal interaction problem while preserving the distinction between body and mind. As much as substance dualism fails on the former count, substance and property monism – or double monism – fails on the latter. Jacquette clinches his case with a particularly powerful example:
What if a history of the Watergate scandal were to be given in a book filled with nothing but chemical formulas describing the brain and other physical events that took place at the time involving participants in the break-in, wire-tapping and cover-up? … Would such a chemical history explain these social-political episodes, even to the neurophysiologist well-versed in understanding chemical symbolism? If anything, it appears that property monist explanations suffer from an explanatory disadvantage in comparison with property dualist accounts of social and psychological phenomena.25
And here we are right back at the relation between society and nature.
While Cartesians spread their intellectual toxin, there was an alternative position: nature and society are material substances tout court, but the one cannot be equated with the other. We have never been in need of being told that we have never been modern, if by this is meant the insight that society and nature cannot be extricated from one another.26 The tribe of historical materialists has always preached as much – indeed, in its very name is inscribed the insistence on human beings as made up of matter, while ‘historical’ implies that social relations cannot be deduced from it. Such relations are exactly as material in substance and utterly unthinkable outside of nature, but they also evince emergent properties different from that nature. Picture a tree. It grows out of the soil, draws nourishment from it, expires the moment it is cut off from it: yet it cannot be reduced to it. Nature is a soil for society, the fold out of which it grew and the envelope it can never break out of, but just as a tree can be told from its soil, society can be differentiated from nature, because it has shot up from the ground and branched off in untold directions over the course of what we refer to as history.27
Bruno Latour, for one, knows this. He is aware that historical materialism has been in permanent opposition to Cartesianism, but he considers it the worst abomination of all – ‘those modernists par excellence, the Marxists’ – because it retains a notion of society and nature as a pair. The error is to perceive a contrast where none exists. ‘The dialectical interpretation changes nothing, for it maintains the two poles, contenting itself with setting them in motion through the dynamics of contradiction’ – worse, it makes ignorance of hybridity ‘still deeper than in the dualist paradigm since it feigns to overcome it by loops and spirals and other complex acrobatic figures. Dialectics literally beats around the bush.’28 The bush, the thorny web of everything, is all there is. One must give Latour credit here for correctly identifying the difference between his approach and that of historical materialism: yes, dialectics is the dance of opposites and requires at least a dyad. Absolute monism rules out dialectics. Only property dualism can capture a dialectics of society and nature.
But what is this ‘society’ we are talking about? We already have a working definition of ‘nature’; one for its counterpart is needed too. A pithy, common-sense equivalent can be readily extracted from the Grundrisse: ‘Society does not consist of individuals, but expresses the sum of interrelations, the relations within which these individuals stand.’29 That thing has developed properties that cannot be found in nature per se. It should now be clear how the matrix of positions in the philosophy of mind maps onto the nexus of nature and society: historical materialism is a substance monist property dualism. It is opposed to both Cartesian substance dualism and hybridist double monism (considering them two sides of the same coin).30 We shall stake out the position in more detail below; for now, let us simply reiterate that there is nothing strange about two things being of the same substance and having distinct properties. Exactly as material, the tree and the chainsaw inhabit the same forest: that is why one can fell the other. But they also follow different laws of motion. That, also, is why one can fell the other.
And so it turns out that double monism has a very pressing causal interaction problem all of its own. If society has no properties that mark it off from the rest of the world – what we insist on calling nature – how can there possibly be such an awful amount of environmental destruction going on?
THE URGENCY OF PROPERTY DUALISM
Substance