The subjective quality of a conscious experience can be understood by how similar it is to all other possible experiences. Similarity relationships are implicitly assessed through the structure of mammalian sensory cortices, allowing effortless knowledge of what an experience is like. This view aligns with perceptual reality monitoring: subjective experience occurs when qualitative sensory information acquires assertoric force. Metaphysical theories generally do not account for these qualitative aspects of consciousness better and may hinder scientific progress.
Consciousness likely emerged during evolution, but its functional role remains unclear. Subliminal priming experiments, which compare conscious and nonconscious processing, show only small, hard-to-replicate effects, and even when functions can operate nonconsciously, consciousness may be needed for them to work fully. New experimental methods that produce strong nonconscious signals are needed. Current evidence suggests consciousness may be less useful than global theories propose; metacognition may be one of the few specific functions to which consciousness contributes.