Full Idea
The three arguments that have been used to articulate the problem of consciousness are the knowledge argument ('Mary'), the possibility of 'zombies' (creatures like us but lacking phenomenal consciousness), and the explanatory gap (the Hard Question).
Clarification
All of them suggest that experience is more than its physical basis
Gist of Idea
The core of the consciousness problem is the case of Mary, zombies, and the Hard Question
Source
Tim Crane (Elements of Mind [2001], 3.26)
Book Reference
Crane,Tim: 'Elements of Mind' [OUP 2001], p.89
A Reaction
All of these push towards the implausible claim that there could never be a physical explanation of why we experience things. Zombies are impossible, in my opinion.