When we observe external objects, we observe their structure and function; that’s all. Such observations give no reason to postulate any new class of properties, except insofar as they explain structure and function; so there can be no analogue of a ‘hard problem’ here. Even if further properties of these objects existed, we could have no access to them, as our external access is physically mediated: such properties would lie on the other side of an unbridgeable epistemic divide. Consciousness uniquely escapes these arguments by lying at the centre of our epistemic universe, rather than at a distance. In this case alone, we can have access to something other than structure and function.

David J. Chalmers, Moving forward on the problem of consciousness, Journal of Consciousness Studies, vol. 4, no. 1, 1997, pp. 3–46, p. 6