The central tenet of functionalism is that mental states (emotions, sensations, beliefs, etc.)
For example: John touches a hot stove, feels pain, and pulls back his hand.
The absent qualia argument is a direct challenge to the functionalist view of the mind that claims that mental states can be defined only in terms of their functional roles, without any reference to the specific physical properties of the brain.
This means that it is a being that behaves almost perfectly like a human, but lacks the subjective, qualitative character of conscious experience.
However, this view fails to account for the fact that mental states are always accompanied by subjective experiences.