Mental Facts Which Are Neither Physical Facts nor Explained in Terms of Physical Facts Exist


I will argue for the view that it is likely that there are such mental facts. I will explain this view by explaining the Causal Exclusion Argument and discussing why I find it inconclusive. I will then discuss a strong argument in favour of mental facts, the Knowledge Argument, and will say why I think a classic counter-argument to it, the Ability Hypothesis, doesn’t succeed.

In this essay, I interpret “mental facts” as anything non-phyiscal that features in accounts of consciousness. An obvious example, would be the facts that exist on the non-physical side of any kind of dualism about consciousness. If a property dualist view about consciousness is held to be likely, then the existence of mental facts is held to be likely. 

However, mental facts are not exclusively a feature of property dualist accounts. Goff (2019, p. 69ff.) supports the Knowledge Argument against physicalism but then argues for a non-dualist panpsychist position. Insofar as that panpsychist view contains things over and above physicalism, it would also contain “mental facts” under this interpretation. Even a physicalist view of consciousness may allow for some mental facts, whilst maintaining physicalism for other facts[1].

The Causal Exclusion Argument

A basic reason why one might find mental facts intuitively implausible is that it is difficult to see how anything non-physical could impact on anything physical, or how a non-physical cause could have physical effects. 

The Causal Exclusion Argument asks us to consider three statements:

  • Mental states are causally efficacious (an intuitive empirical notion)
  • Mental states are not part of the physical domain (a non-physicalist view)
  • No physical event has a cause outside of the physical domain (causal closure of the physical)

These statements cannot all hold true at the same time. The physicalist is happy to give up the second statement and conclude that mental states are part of the physical domain. I will discuss one of the arguments, the Knowledge Argument, below that suggests to me that a physicalist view of consciousness is less plausible than dualist alternatives. 

The dualist has two choices: Epiphenomenalism denies (1), accepting that mental states are a mere epiphenomenon of physical processes. This is unattractive, as it leaves mental states as “nomological danglers” (Smart, 1959, p. 142, citing Feigl, 1958, p. 428) with no function. 

More strangely, it leads to a situation where our claims to have consciousness, our believing in, our talking and writing about consciousness and conscious experiences are not explained by us having such experiences – they are not causally efficacious, so couldn’t make us think, talk and write about consciousness – but would have to be explicable by some physical processes on which consciousness itself has no bearing.[2]


To my mind therefore the more attractive notion is interactionism, i. e. denying (3). It is difficult to see how the laws of physics can accommodate the suspension of causal closure. Goff (2017, p. 77), for example, raises problems for the principle of conservation of energy: “If the immaterial mind [for which we could also substitute non-physical properties] acted on the brain, then this would add energy to the brain that had not previously been there, thus violating the principle that energy in the physical universe is always conserved at the same level.” 

More problematically though, there is no evidence of any “novel” causal powers – not observed by physics elsewhere – operate in the brain of conscious beings, or that rising complexity of physical structures, such as exists in brains of conscious beings would lead to the emergence of novel physical laws. 

An argument could be made that given the incompleteness of our understanding of physics, in particular perhaps in remaining uncertainties about areas of quantum theory, there may yet be a hope that mental-physical interactions could be accommodated, once these areas are filled in. Goff (2017, p.77), eg., suggests that there may be psycho-physical laws that work together with other laws of nature to respect energy conservation.

The interactionist’s most fundamental response to the challenge “why can’t physics find the laws and mechanisms for this mental-physical interaction,” is to deny that physics has a claim to be the right or the exclusive approach to finding the laws and mechanisms in question. Crane and Mellor (1990) provide a number of ways in which it is doubtful that physics is in any way more fundamental or basic than, say, psychology. Nagel (1986) goes further than that in arguing that the fact that physics – as an approach to saying something about the nature of things – specifically looks to subtract any kind of first-person perspective, which makes it particularly unsuitable to saying things about the nature of conscious experiences:

“For many philosophers the exemplary case of reality is the world described by physics, the science in which we have achieved our greatest detachment from a specifically human perspective on the world. But for precisely that reason physics is bound to leave undescribed the irreducibly subjective character of conscious mental processes, whatever may be their intimate relation to the physical operation of the brain.”  (Nagel, 1986,  p. 15)

In other words, physics has a “blind spot” with regard to consciousness, not because it is incomplete in respects that would – when eventually filled in – enable it to say more, but because it is central to its method to subtract conscious experience from its view of the world. And if the mechanisms for mental-physical causation cannot be found by the methods of physics, it does not necessarily mean that they do not exist, merely that we should not expect to find them through those methods alone.

The Knowledge Argument

Having said something about why I don’t find physicalism about consciousness compelling, I will now turn to the argument that I think best illustrates the case for property dualism. The Knowledge Argument is often illustrated by a classic thought experiment: Imagine Mary, a neuro-scientist who specialises in colour perception. She has lived her whole life in a black-and-white room, perceiving the world through a black-and-white television screen. Under those circumstances she has learned every bit of physical knowledge about colour perception. One day she is let out of her black-and-white room. For the first time in her life, she sees a red tomato and – for the first time in her life – perceives something red.  At that moment she gains a new understanding of colour. She gains a new piece of knowledge: what it’s like to perceive red.

What this illustrates is that the totality of physical knowledge, is not the totality of knowledge about colour perception. Crucially, the totality of physical knowledge about colour perception does not include knowledge about what it is like to perceive colour. This is non-physical and additional, a mental fact. The knowledge argument then is that no amount of physical knowledge about conscious experience will contain the knowledge of what it is like to have that experience.

The Ability Hypothesis

A counter-argument to the knowledge argument has been put forward by Nemirow (1980). He argues that Mary does not acquire new knowledge about facts when she sees something red for the first time. Instead, Nemirow (1980) argues, Mary acquires an ability. Understanding an experience, according to this view, is the “ability to place oneself, at will, in a state representative of the experience. I understand the experience of seeing red if I can at will visualise red.” (Nemirow, 1980, p. 475).

Nanay (2009) highlights a flaw with this and other versions of the Ability Hypothesis. In a generalised way, Nanay summarises various versions of the hypothesis as “knowing what it is like to have experience E is just having the ability to imagine or recognise or remember having experience E” (2009, p. 699). This is a fairly simple version of the hypothesis. But, first, Nanay argues, it is possible to imagine having experience E wrongly (p. 702). Second, Nanay draws attention to people who become blind later in life. Such people would know what it is like to experience red, but would lack the ability to recognise red; and they lack the ability to imagine red in such a way that it would help them to recognise red (p. 704).

Nanay does not think that these objections need be fatal to the Ability Hypothesis. But the hypothesis needs revision. Nanay’s suggestion is that: “Knowing what it is like to experience E is having the ability to distinguish imagining or having experience E from imagining or having any other experience” (p. 705). This is now a much more complex version of the hypothesis.

In arguing for the ability hypothesis, Nemirow (1980, p. 475) suggested that Nagel’s (1980) “understanding of understanding is too naïve.” Nemirow suggests that Nagel assumes “that understanding an experience consists in grasping facts about the experience.” However, he suggests, understanding can also consist “in the acquisition of abilities”  (Nemirow, 1980, p. 475).

I think it is likely that there are examples of ability acquisition that don’t involve knowledge or grasping facts. I think mainly of things like being able to ride a bicycle.[3] Learning this skill is a process of acquiring the ability to balance, pedal, steer and being aware of what is around and ahead at the same time in a way that results in a fluid movement. The example that Nemirow (1980, p. 475) gives, that of “understanding a language,” I think, is more controversial. There may be instances of people who acquire such an ability without grasping facts. But even so, I would argue that standardly, understanding a language is partly about having acquired an ability, but also partly about grasping facts, for example, about how the grammar and syntax work. 

If we accept then that “understanding” could mean something on a spectrum between acquiring an ability without grasping facts on one end and grasping facts without acquiring an ability on the other, then the simple formulations of the ability hypothesis may just be at the ability-without-facts end of the spectrum, whereas, I would argue, Nanay’s more complex formulation looks very much further down the spectrum towards needing to grasp some facts. 

I can’t see how the ability to distinguish having or imagining an experience from having or imagining a different experience (Nanay’s more complex formulation) cannot involve some knowledge, primarily of what the experiences that are being distinguished from each other are like. Nanay may not be particularly worried about that, as he wants to remain neutral about the implications of the Ability Hypothesis as a physicalist defence against the Knowledge Argument (p. 701). But I think those who do want to use the Ability Hypothesis as a defence against the Knowledge Argument may find Nanay’s formulation more difficult to work with.

Papineau (2002) convincingly argues that Mary acquires knowledge that allow her to have new kinds of thoughts about colour, when she starts having colour experiences:

“Imagine that she is shown, not a rose, but a coloured sheet of paper, so she has no way of knowing, in her old material terms, which colour experience this is. She might be able to figure out that it is a colour experience, but there is nothing to tell her whether she is seeing something red or green or blue. This shows that Mary cannot be thinking just using her old material concepts.” (p. 62)

When Mary later sees something she knows to be red and has a thought like “so this is what red looks like,” “this” picks out something according to Papineau that was not previously available as a concept to Mary, but now is. What “this” picks out is a new phenomenal concept that is additional to Mary’s old material concepts. 

Papineau (2002, p.62) concludes that Mary acquires a mix of abilities and knowledge when she starts having colour experiences: “There is a sense in which Mary’s new powers of imaginative re‐creation and introspective classification are indeed new abilities—she can certainly do things she could not do before. But they are not mere abilities, if that is taken to rule out her possession of new phenomenal concepts[4].”

ConclusionI have aimed to explain why I find it likely that there are mental facts starting with my doubts about the Causal Exclusion Argument. As a part of this, I have argued that we shouldn’t rule out interactionism as a possibility and expressed sympathy for the view that we shouldn’t overstate the authority of physics to provide a full explanation of consciousness. I have described the Knowledge Argument and why I think the Ability Hypothesis does not invalidate it. This leads me to a tentatively property dualist view about consciousness. I am tentative in these conclusions, as I feel that I have only scratched the surface of thinking about consciousness here.

[1] See Kim (2002, p.643) “We are therefore left without an explanation of how qualia can be causally efficacious; perhaps, we must learn to live with qualia epiphenomenalism.”

[2] I am following Open University (2021).

[3] I only spotted after writing this that Papineau (2002, p. 61) also uses this as an example of where the Ability Hypothesis might apply.

[4] Papineau (2002) argues against the Ability Hypothesis but against property dualism.

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