David Chalmers is an Australian philosopher at NYU whose formulation of the hard problem reorganised the philosophy of mind around a single distinction.

The hard problem

In 1995 he separated two kinds of question about consciousness. The easy problems concern function — how a system discriminates stimuli, integrates information, reports its own states, controls behavior. They are difficult in practice and tractable in principle, because each asks how a mechanism performs a task.

The hard problem asks why performing any of those functions is accompanied by experience at all. A system could in principle do everything a person does with nothing it is like to be it. Explaining the function appears to leave the experience entirely untouched, and that gap is what makes the problem hard.

The word "easy" was ironic and has been misread ever since.

Zombies

His supporting argument asks you to conceive of a being physically identical to a person and entirely without experience. If such a being is conceivable, and conceivability is a guide to possibility, then experience is not fixed by physical facts alone.

Critics attack both steps — whether a zombie is genuinely conceivable, and whether conceiving something shows it possible. The argument remains the clearest statement of what a physicalist account has to explain away.

What he proposes

Chalmers takes the gap seriously enough to consider treating experience as fundamental, alongside mass and charge, rather than as something that emerges. That leads toward panpsychism, a position he presents as worth taking seriously rather than as established.

The extended mind

With Andy Clark he argued in 1998 that mental processes can extend beyond the skull into the tools a person reliably uses — a notebook doing the work of memory is part of the cognitive system rather than an aid to it.