Easy problems and the hard problem
Philosopher David Chalmers introduced the distinction in 1995. The "easy" problems are explaining functions: how the brain discriminates stimuli, integrates information, reports its states and controls behaviour. They are enormously difficult in practice, but we know what a solution would look like: a mechanism that performs the function.
The hard problem is explaining why performing those functions feels like anything. Even with a complete wiring diagram and a perfect model of every signal, it seems we could still ask why all that processing is not happening "in the dark".
The explanatory gap
Philosopher Joseph Levine called this the explanatory gap in 1983. Learning that pain involves certain nerve fibres firing tells us what happens physically, but it does not seem to explain why it hurts. Many famous thought experiments press the point, such as philosophical "zombies": imagined beings that behave exactly like us but experience nothing.
The main responses
- Physicalist optimism: the gap reflects our current ignorance. As neuroscience advances, the hard problem will dissolve, much as "what is life?" did once biology explained metabolism and reproduction.
- Illusionism: the sense that experience is something extra is itself a product of how the brain models itself. Explain that self-model and you have explained everything that needs explaining.
- Non-reductive views: experience is a fundamental feature of reality, alongside mass or charge, so it cannot be fully derived from physical processes.
- The "real problem": Anil Seth suggests focusing on explaining, predicting and controlling specific properties of experience. Progress there may gradually shrink the hard problem.
Why it matters for AI
If we cannot fully explain why brains are conscious, we cannot simply read off whether a machine is. That is why we treat the question as an empirical programme. The aim is to find measurable signatures that reliably track consciousness in brains, then ask whether artificial systems share them, while staying honest that a signature is not the same as a solution.
Our research sits on the boundary Chalmers drew. We ask whether mathematics can capture a measurable difference between a system that processes information and one with the integrated, self-representing organisation that conscious brains seem to have. That would not dissolve the hard problem, but it would turn part of it into something we can test.
Quick answers
What is the hard problem of consciousness in simple terms?
It is the question of why physical brain processes are accompanied by subjective experience at all, rather than happening without anything being felt.
Who came up with the hard problem?
Philosopher David Chalmers named and framed it in 1995, building on earlier work such as Thomas Nagel's 1974 essay and Joseph Levine's 1983 'explanatory gap'.
Further reading
- Chalmers, D. (1995). Facing up to the problem of consciousness. Journal of Consciousness Studies, 2(3).
- Levine, J. (1983). Materialism and qualia: the explanatory gap. Pacific Philosophical Quarterly, 64.
- Nagel, T. (1974). What is it like to be a bat? The Philosophical Review, 83(4).
- Seth, A. (2021). Being You: A New Science of Consciousness. Faber & Faber.