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About DONATE NEWSLETTER MENU / NEWSLETTER / SIGN IN A cat sitting on a worn red sofa with scattered cushions against a textured beige wall. i Is everything conscious? If the question makes no sense to you, try spending some time with the principle of sufficient reason Sam Kimpton-Nye
is a lecturer in philosophy at the University of Southampton, UK. He is the co-author, with Toby Friend, of Dispositions and Powers (2023).
Edited bySam Dresser 4,500 words Save
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When an explanation makes a fact intelligible, the mystery goes out of it. We understand it so well that we can hardly conceive of things being otherwise. Consider the simple mathematical fact that one plus one equals two. Once we understand elementary arithmetic, we no longer feel the urge to ask why one plus one equals two. That one plus one equals two strikes us as not merely true but unavoidable; we cannot even coherently imagine its falsity. Much of philosophy aims to bring other fundamental features of reality into a similar light, to make them appear not arbitrary but inevitable and, thus, intelligible.
This aspiration that philosophy render the world intelligible is best expressed by the German polymath Gottfried Wilhelm Leibniz and the Dutch philosopher Baruch Spinoza. According to Leibniz: ‘we can find no true or existent fact … without there being a sufficient reason why it is thus and not otherwise.’ And, as Spinoza wrote: ‘For each thing there must be assigned a cause or reason, both for its existence and for its nonexistence.’ What’s being expressed here, in the words of the US philosopher Michael Della Rocca, is the desire ‘to make the world and our place in it intelligible’. To grasp the kinds of reasons or explanations sought by Leibniz and Spinoza ‘is the perennial hope and promise of philosophy’.
The demand for intelligibility can lead to some extraordinary places. For Leibniz, the demand led him to propose that reality is ultimately made up of a multiplicity of monads: indivisible, infinitesimally small units of substance, each of which is a causally isolated, self-contained universe. Spinoza’s resolute commitment to universal intelligibility led him to conclude that reality is, instead, a single infinite substance that he called God or nature. As we will see, the demand for intelligibility can also lead into the strange and fascinating world of panpsychism.
Panpsychism is an increasingly popular view about consciousness. You are conscious, you feel pleasures, pains and all manner of other experiences. At every waking moment, and even when you dream, there is something that it is like to be you. The same goes for other humans and animals, and this accounts for moral status: thumping a fist on a desk in frustration is morally permissible in a way that hitting a conscious person or animal is not. Desks, chairs, rocks and so on are not conscious – and are therefore without moral status – whereas humans, bonobos, dogs and so on are conscious, and deserving of at least some moral recognition. But panpsychism rejects this division into conscious and non-conscious things. It is the view that consciousness is a fundamental property of matter, so everything from electrons and protons to tables and planets, and, of course, humans and dogs, has consciousness to some degree.
Panpsychism is a remarkable thesis, motivated by the ‘perennial hope’ that the world is ultimately intelligible. To investigate whether panpsychism truly can make the world intelligible, we will explore three different arguments, each of which is grounded in a principle that crystallises the ambitious aim of universal intelligibility: the principle of sufficient reason (PSR). This simple and plausible principle of philosophical enquiry – that there exist satisfying explanations for everything – can lead to a whole new understanding of the nature of reality. And, though I’m sceptical about the availability or even desirability of explanations that dissolve all the world’s mysteries, there is exceptional value in the mere contemplation of such projects.
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If you come home from work to find a bouquet of flowers on your doorstep, there will be a reason for this. Maybe it’s a birthday present, a congratulations on a new job, a thank you for some good deed. If your car dashboard shows a warning light, you’d be wise to assume that there is some reason for this, such as a problem with the engine, fluids or tyres. The Chicxulub crater, 200 km wide and 1 km deep, in the Yucatán peninsula in Mexico, cries out for scientific explanation, which is precisely what the hypothesis of an extinction-level asteroid impact millions of years ago provides.
But is there really a reason for everything? The mass of a proton is 1.672 × 10-27 kg. What’s the reason for this? What’s the reason for a particular radioactive decay event to which our best scientific theory on the issue, quantum mechanics, assigns only a probability? According to the PSR, there is indeed a reason for everything. For any way the world is, from the flowers on your doorstep to the mass of a proton, there is some reason why it is this way and not some other way. All facts have a reason, and – according to the PSR in its strongest form, as defended by Spinoza – that reason makes them intelligible and necessary, and their contrary inconceivable.
Though the PSR found its fullest expression in Leibniz’s work – ‘The fundamental principle of reasoning,’ Leibniz wrote, ‘is that there is nothing without a reason’ – its lineage is far greater. As Della Rocca showed in his book Spinoza (2008): ‘Versions of [the PSR] go way back in philosophy and can be found in philosophers such as Parmenides, the Stoics, [and] Aquinas.’ And the principle is not restricted to Western European philosophy. It occupies a key position in the metaphysical system of the Islamic philosopher Ibn Sīnā (also known in Europe as Avicenna), who used it to argue that things that exist merely contingently – that is, things whose existence is not necessary – must have a cause outside themselves. Versions of the principle have also been defended in contemporary metaphysics and philosophy of physics. Shamik Dasgupta has argued that every substantive fact has a metaphysical grounding that makes it necessary. And Eddy Keming Chen has developed a physical model of the Universe according to which every single fact (from the number of hairs on your head at 2 pm this afternoon, to the mass of the electron) is entailed and thus explained by the laws of nature.
The PSR is so alluring because it would seem that the very activity of enquiry – whether philosophical, scientific, or the first ‘Why?’ question of a young child – is premised on there being an explanation, a reason, for everything. To endorse the PSR is to adopt an attitude of optimism that the world and our place in it are intelligible and infused with reason and meaning. If anything were unexplainable, there’d be a grave risk that human enquiry is ultimately futile. The falsity of the PSR would constitute a fundamental mismatch between our inquisitive nature and the world in which we find ourselves; it would imply that the world is unintelligible.
The optimistic attachment to intelligibility and reason comes at a significant cost
Intelligibility and meaningfulness are two sides of the same coin. When, on reflection, we can find no good reason for our personal and professional pursuits (lining the boss’s pockets won’t generally satisfy us!), when these things seem absurd or unintelligible, it’s natural to express the predicament in terms of a lack of meaning in life. Analogously, failure to uncover satisfying answers to questions about the nature of reality can lead to deep philosophical worries that the world itself is ultimately meaningless.
But this is not to say that the PSR is universally accepted among philosophers. It is controversial because it seems to entail necessitarianism – the thesis that everything is necessary. You are currently reading an essay about the PSR and panpsychism, but you could have been doing something else. If the PSR is true, however, then there is a sufficient reason why you are currently reading this essay, which makes it necessary that you are currently reading this essay and hence impossible that you could be doing anything else. Since the PSR applies to everything, it seems to entail the necessity of everything, and many find this unpalatable because it threatens free will and the seemingly obvious fact that all manner of things could have been different in all sorts of ways.
Contemporary philosophers who describe themselves as ‘Humean’, that is, as influenced by the Scottish Enlightenment philosopher David Hume, are explicit in their rejection of necessity and ultimate explanations. David Lewis, perhaps the most prominent Humean of the past century, maintained that ‘all there is to the world is a vast mosaic of local matters of particular fact, just one little thing and then another.’ That is to say, there are no reasons, and no necessity for what goes on in the world. In a similar spirit, the Dutch American philosopher Bas van Fraassen consistently challenges the need for a metaphysical explanatory structure. This manifests itself in the rejection of robust laws of nature that necessitate events in the Universe. Science, according to Van Fraassen, can get along just fine without deep explanations that make things necessary.
So, the optimistic attachment to intelligibility and reason comes at a significant cost: it demands a commitment to widespread necessity. There are, however, ways of mitigating this cost. Various authors, including Leibniz himself, have argued that the PSR is at least consistent with a sense in which things could have been different, and this will correspond to weaker senses of explanation. The strongest explanations, those that yield necessity, can be demonstrated in a finite number of steps; prime examples include mathematical and geometrical demonstrations. Other explanations are not finitely demonstrable, though they can be perceived by the infinite mind of God. But the fact that some explanatory connections cannot be grasped by our limited human intellect suffices, according to Leibniz, for contingency.
Alternatively, one could embrace necessitarianism, as Spinoza does, and see it as just another positive facet of the interconnectedness and intelligibility of all things – this seems the way to go if one is to maintain the courage of one’s conviction as a philosophical optimist. But necessitarianism is not the only controversial upshot of the PSR. It can also motivate panpsychism.
Perhaps the most elusive question in all of science and philosophy concerns the nature of conscious experience. Why are the arrangements of matter that constitute human beings and other animals accompanied by conscious experience? Why is there something that it is like to be you? Why are some physical states, but not others, conscious? However completely we describe the physical arrangements of matter that make up a conscious being, that description leaves out the very thing we’re trying to explain: what it feels like from the inside. This challenge to provide an explanation that bridges the gap between third-person scientific descriptions of matter and first-person conscious experience is what the Australian philosopher David Chalmers dubbed the ‘hard problem of consciousness’.
The question is so fiendishly hard because it does not seem amenable to scientific methods of enquiry. The operation of a mill, for example, can be explained by its components: water flow rotates a wheel, which drives gears connected to millstones, which grind wheat into flour. The whole operation of the mill and its output (flour) can be made intelligible to us. If we ask ‘Why does the mill produce flour?’ a fully satisfying answer can be given. No mystery remains.
The mill example is illustrative of scientific explanation in general. The boiling point of water is explained in terms of the hydrogen-bonding of H2O molecules, and the path of light around a massive celestial body is explained in terms of the curvature of spacetime described by Albert Einstein’s general theory of relativity. These cases take more work to understand, but the principle is the same as in the mill case.
If consciousness is a fundamental property of matter, then the problem of explaining consciousness does not arise
However closely we look at the physical matter that makes up conscious beings, we get no closer to understanding how consciousness arises. Leibniz encouraged us to imagine increasing the size of the human brain to the size of a mill so that we can walk around inside it and observe all its working parts in meticulous detail. If we did this, at no point would we observe conscious experience. Conscious experience, by its very nature, is private, first-personal. Since scientific methods can yield knowledge only of the objective, third-person-accessible facts regarding matter in motion, there is an essential mystery concerning the origin of consciousness. The question of why some physical states, but not others, are conscious seems unanswerable.
Unanswerable questions do not sit comfortably with our inquisitive human nature. If consciousness cannot be explained in principle, this would be a particularly egregious violation of the PSR. However, it is worth considering our options for explaining consciousness and, thus, upholding the PSR once we accept that reductive scientific explanation is not up to the task.
One option is to understand consciousness in terms of a new substance entirely, one fully distinct from physical matter. On this view, reality is bifurcated into physical substance characterised by spatial extension, and mental substance characterised by thought, where the latter accounts for consciousness. This is called dualism. The most influential champion of dualism was the French philosopher René Descartes. But Descartes ultimately failed to uphold the PSR, since he couldn’t say why there are two substances as opposed to just one.
Alternatively, we could question the seemingly obvious assumption that fundamental physical matter isn’t conscious. The mystery arises because there is no way to understand how non-conscious physical matter, arranged in space and time, can give rise to consciousness. But why must we think that fundamental physical matter is not conscious? This assumption is not mandatory. If consciousness is a fundamental property of matter, then the problem of explaining consciousness, as formulated above, does not arise. So, in the interest of avoiding this in-principle obstacle to explaining consciousness, many are inclined to believe that consciousness is a fundamental property of matter, that panpsychism is true.
The hypothesis that fundamental matter is physical and non-conscious blocks the possibility of an intelligible explanation – in terms of the fundamental ‘bits’ of matter – of why creatures like us are conscious. If consciousness is absent at the fundamental level, there will always be an explanatory gap between the physical and the mental. What this means is that, for any arrangement of physical matter constitutive of a conscious being, it always seems possible that consciousness was absent; no arrangement of matter seems to be necessarily connected with, and hence able to explain, consciousness. But if consciousness is introduced at the fundamental level, this obstacle is removed. According to panpsychism, we no longer need to bridge the gap from non-conscious fundamental matter to consciousness at higher levels of organisation, since consciousness is present all the way down.
There is still significant work to be done to explain how fundamental consciousness combines to create human-level consciousness. But, at the very least, panpsychism offers a way of avoiding what would otherwise appear to be a potentially devastating violation of the PSR. If consciousness is already present at the fundamental level, there is no longer the same pervasive explanatory gap between wholly non-conscious matter and conscious beings at higher levels.
There is another route to panpsychism via the PSR. The Norwegian philosopher Hedda Hassel Mørch argues that fundamental consciousness is required to properly explain the basic motions of matter, documented by fundamental physics. Science tells us plenty about how matter behaves and what different subatomic particles such as protons, electrons and neutrons do. But it does not tell us what matter is. This is evident from the way in which science characterises matter. The electron, for example, is characterised in terms of its properties: mass, charge and quantum spin. And these properties, in turn, are understood in terms of how they dispose the electron to behave. What is absent from this scientific description of the world is an account of what physical properties are like in themselves, and hence why they have the power to dispose matter to behave in certain ways.
Why do the properties of an electron dispose it towards certain behaviours? How can this be rendered intelligible as per the demands of the PSR? Consider pain. If you are in pain, this mental property disposes you to avoid the thing that’s painful: accidentally touch a hot radiator, and you’ll instantly remove your hand. As Mørch puts it: ‘In the absence of any interfering motives, it seems pain always makes subjects try to avoid it, and [it is] difficult to conceive otherwise.’ If we ask why someone withdrew their hand from the radiator, it is a perfect explanation to say that the heat caused them pain. The explanation renders the action fully intelligible because part of what it is to be in pain is to try to avoid the painful source. Mental properties are special in that they are the only properties with this ability to provide intelligible explanations of behaviour. As Mørch writes:
The only fundamentally dispositional properties we know or can positively conceive of are phenomenal properties – in particular, phenomenal properties associated with agency, intention and/or motivation.
Other properties, such as negative charge, could, for all we know, have disposed things to behave very differently or in no systematic way at all. But it is inconceivable that pain disposed us to do anything besides avoid the source of pain. ‘It does not,’ Mørch writes, ‘seem conceivable that pain makes subjects try to do anything else than avoid it in virtue of its intrinsic character alone.’ This raises a fascinating prospect. In the interest of rendering the behaviour of matter intelligible, we should take those properties responsible for that behaviour to be conscious mental properties. That is to say: all paradigm physical properties such as charge, mass and quantum spin are conscious mental properties. This move provides an answer to the question of what matter fundamentally is, which, in turn, explains why matter does what it does. The fundamental properties of matter are properties of consciousness. By their very nature, they dispose the matter of which they are properties towards certain behaviours. This plugs the explanatory gap left by the scientific method alone. Again, the primary motive in this argument is the desire for intelligible explanations of the world, as per the PSR.
For Spinoza, if things depend on properties because properties individuate things, then it follows that properties are more fundamental than things
There is a third way that a commitment to the PSR leads us to panpsychism. Spinoza is perhaps most famous for h