How does materialism explain thoughts and sensations without using immaterial substances?

Materialism explains thoughts and sensations by identifying mental states with physical processes, thereby avoiding the need for immaterial substances like the soul. Several key theories have been developed to account for this:1

• Identity Theory: This view posits that mental states are identical to physical states of the brain or central nervous system. While early "type-type" identity theory faced objections regarding multiple realizability, "token-token" identity theory suggests that specific instances of mental states are identical to particular physical brain states.2
• Functionalism: This theory defines mental states by their causal roles—how they respond to sensory input, interact with other mental states, and produce behavior—rather than their specific physical composition. It draws an analogy between the brain as hardware and the mind as software.3
• Analytical Behaviourism: This approach argues that talk of the mind is not about an entity at all, but rather a description of how individuals would behave in specific circumstances.1
• Eliminative Materialism: This radical view contends that "folk psychology" terms like beliefs and desires are inaccurate. It suggests that these concepts should be eliminated in favor of a purely scientific, neurophysiological description of how the brain functions.4

Despite these efforts, philosophers note an "explanatory gap," as it remains difficult to account for subjective experiences, or "qualia," solely through physical descriptions.54