In 1994 the philosopher David Chalmers raised questions about consciousness that ignited a zombie apocalypse.
These weren’t questions no one had asked before. These were questions that rattled the modern orthodoxy. Many people assumed that advances in science had settled questions about an immaterial mind or soul. According to the modern story, science had exorcised that ghost from the machine and neuroscience would eventually explain consciousness.
Then Chalmers released the philosophical zombies, and the war began.
What is a philosophical zombie?
Rather than the blood-stained reanimated corpse of horror films, a philosophical zombie is less frightening. It’s an explanatory nightmare.
Imagine your doppelganger, a being physically identical to you, atom for atom. The only difference is the doppelganger has no consciousness. They look happy or sad, they even tell you of their hopes and dreams.
From the outside they’re indistinguishable from a normal human. But from the inside the zombie is a hollow imitation. There’s no inner experience. They groan and complain of headaches, but they feel no pain. That’s a philosophical zombie. The physical structure, functions and behaviour are identical, but there is no consciousness.
What exactly is the missing ingredient?
Consciousness is an ambiguous term. It can be used to describe the difference between being asleep and being awake, or having the ability to react to information, focus attention and other similar cognitive abilities. Chalmers calls these the easy problems of consciousness to contrast them with the hard problem. He says,
“The really hard problem of consciousness is the problem of experience. When we think and perceive, there is a whir of information processing, but there is also a subjective aspect.” ¹
Philosophers call this subjective experience qualia, or “what it is like”. There is something it is like to taste a lemon, which is different to what it is like to do your income taxes, or listen to fingernails scraping down a blackboard.
The rich and distinctive inner feel of all these experiences is different. That inner world is so familiar, so fundamental to our existence we rarely question it or notice how extraordinary consciousness is. It’s this aspect of consciousness, the inner feel or conscious experience, that the zombie lacks.
Why is it a hard problem?
The difference between the easy problems and the hard problem shows the challenge for a scientific explanation of consciousness.
“The easy problems are easy precisely because they concern the explanation of cognitive abilities and functions. To explain a cognitive function, we need only specify a mechanism that can perform the function. The methods of cognitive science are well suited for this sort of explanation and so are well suited to the easy problems of consciousness.”²
Explaining the difference between being asleep and being awake only requires a description of brain processes responsible for the contrasting behaviour. All it means for a system to be awake is to be receptive to information from the environment and use this information to direct its behaviour. The state we call awake is a functional state.
Explaining a functional state requires specifying a mechanism that performs the function. Scientific reductionist explanations work on the principle that we can understand all phenomena by explaining their elementary parts. A description of the structure, functions, and interactions of those parts is all we need to completely explain any phenomenon.
But when it comes to conscious experience, this sort of reductive explanation fails. Even if we have a complete explanation of all structure and function, there will always be a further unanswered question: Why is this function accompanied by experience? Why is there an inner feel?
No reference to mechanism can answer that question. Which means there can be no reductionist explanation.
Isn’t it enough to explain the functions?
All this may seem like an intellectual chimera, everyone knows zombies aren’t real, so does it matter? The point of zombies isn’t that they could exist in the actual world. Zombies are a thought experiment designed to test if consciousness is logically entailed by the physical facts.
And that matters for the philosophy of physicalism.
For the physicalist, it’s an explanatory nightmare. The stakes are high. If there can’t be a scientific explanation of conscious experience, that puts physicalism in serious doubt.
Physicalism is the claim that the only type of things which exist are physical things. Exactly what counts as physical can be defined in different ways, but generally speaking, physicalism says everything that exists can be explained by the laws of physics; or is fully reducible to things that can be explained by the laws of physics.
If science is restricted to reductive explanations, but no such explanation can include conscious experience, then science cannot explain it. Many people take it for granted that cognitive science will eventually explain consciousness. Chalmers’ distinction puts the truth of that in jeopardy.
Science can explain the easy problems. Easy is an understatement, the easy problems will take many years of advanced research. But in principle there is no real difficulty. They’re all the sort of problems we expect science to solve because they deal with structure and functions.
The hard problem is different. Hard is also an understatement, it’s a euphemism. It really means impossible.
Conscious experience is a phenomenon which, in principle, science can’t explain.
Confronting the nemesis of the scientific method — why is anyone surprised?
When we consider what the scientific method consists of, this apocalypse is predictable.
The philosopher Thomas Nagel argues that the scientific method creates the mind-body problem and with it the hard problem of consciousness. Science is a method of inquiry that intentionally excludes certain features from its explanations.
The excluded features are first-person experiences. Science only deals in quantitative, objective, third-person properties. By describing red in objective features as wavelengths of electromagnetic radiation, we’ve stipulated that science must exclude the experience of seeing red from any explanation.
The observed nature of the world didn’t demand this restriction. It was a stipulated demand that only certain aspects of the world could be included in scientific explanations.
So it shouldn’t be a surprise that when science confronts the fundamental properties of the mind, it finds itself incapable of breaching the divide.
Because it intentionally created the divide.
The physicalist trilemma
The mind-body problem arises from the intersection of three observations, creating a trilemma –
- Consciousness is non-physical.
- The physical world is causally closed, all physical effects have physical causes.
- Consciousness is causally effective. Mind affects body.
All three can’t be true simultaneously, so we must deny one to avoid logical contradiction.
Physicalist responses to the trilemma
The physicalist must deny the first observation, they have no choice. If it’s true that consciousness is non-physical, then not everything is physical, and physicalism is false.
The physicalist must accept the second, the causal closure of the physical. If causal closure is false then not every physical effect has a physical cause, and again physicalism is false.
Denying the third means consciousness doesn’t have any causal power. When you move to the fridge because you want a snack, or take medication because you feel pain, or lock the doors because you’re afraid of burglars, it seems obvious those conscious states cause your actions. But epiphenomenalism denies they do.
Epiphenomenalism isn’t fatal to the physicalist theory, but it puts it on critical life support. Our mental states cause actions which move matter constantly, giving us strong evidence it’s true. Any arguments those powers are illusory will need to be stronger than our confidence our conscious states cause our bodies to move.
Which is why the most popular option for the physicalist is to deny the first observation that consciousness is non-physical.
Denying that consciousness is non-physical
Physicalists have two broad options if they want to deny that consciousness is non-physical. They can agree that consciousness has non-physical properties, but argue those properties are fully reducible to physical properties like brain processes. This is a property dualism, consciousness is a property of brains like liquidity is a property of water.
This option avoids the immediate danger of consciousness being non-physical, but it creates more problems. They still need to confront the hard problem of showing how physical mechanisms produce non-physical properties. But now they also have two new problems, causal over-determination and top-down causation.
If property dualism is true, those non-physical properties have causal power. But this means we have causal over-determination. We have the physical causes (whatever physical things consciousness reduces to) and the non-physical properties as causes.
My fear of burglars causes me to move my body, but fear isn’t a physical property. Even if fear is shown to be reducible to a brain state, now both the brain state and the experiential state of fear are causes. Our causal explanations are overdetermined.
It also means the causation proceeds from the non-physical properties to the physical, from the top down. But that violates causal closure which says all physical effects have physical causes.
A second option, which is a minority view among physicalists, is to deny there is any problem to be explained. They argue that once we’ve explained all the functions and mechanisms, there is nothing left to explain. That we think there is a problem is only a result of ignorance, as was the case when it was proposed life couldn’t be explained without theorising the existence of a vital force (elan vital).
However, this line of argument ignores the unique nature of consciousness. Consciousness isn’t an explanatory postulate, something like elan vital that we theorise exists to explain some other thing (life). Conscious experience is the thing to be explained. So it’s not possible to eliminate the phenomenon in this way.
The end of physicalism as we know it?
Confronting the hard problem of consciousness has led many philosophers to propose an expansion of physicalist ontology. Consciousness must be added to the fundamental constituents of reality, like space or time.
These are fundamental properties that are elementary and basic. They aren’t themselves explained but instead form the explanatory framework which contains the explanations.
It isn’t our conception of consciousness that needs to change, it’s our conception of matter. The mechanistic philosophy views matter as an insentient machine.
This arose from the habit of seeing matter that way because it was practical for scientific investigation. From that way of seeing the world, many came to believe the world was really like that. A naturalist method morphed into a metaphysics.
Modern physics has already moved beyond the simple mechanical picture of nature, yet when it comes to metaphysics, we still labour under the mechanistic paradigm from the age of Newtonian physics.
All these problems are only problems for the physicalist. Alternative metaphysical views, like idealism, substance dualism, or panpsychism, avoid the hard problem by denying causal closure. They accept that consciousness is non-physical and causally effective, which means causal closure must be false.
Unlike the observations of the properties of consciousness and its causal powers, causal closure isn’t based on observations of the world. It’s a metaphysical commitment. Physicalism is confronting a problem created by its philosophical commitments being in conflict with our observations of the world.
The reason science is so successful is it adapts the theory to fit the data. Consciousness isn’t an explanatory posit, it’s the datum we want to explain. If our metaphysical framework can’t accommodate the data, rather than try to eliminate or reinterpret the data, we should conclude that the explanatory framework is incomplete.
All quotes from David Chalmers, The Character of Consciousness
- page 5 and 2. page 6
Image credit: Compare Fibre on Unsplash
Unity in Difference 