token-token identity theory

The identity theory in philosophy, a form of materialism, posits that mental states are identical to physical states. This view suggests that phenomena like thoughts are reducible to processes in the brain, such as neural activity. The primary argument for this theory is its economy in explaining the world and unifying causal claims, as mental events are considered physical events themselves.12

However, a challenge arises from the possibility of different physical compositions leading to the same mental state, such as beliefs or mental images. To address this, a distinction is made between "type-identity" (every type of mental phenomenon is a type of physical phenomenon) and "token-identity" (every mental phenomenon is identical to some physical phenomenon). While token-identity is considered more plausible, issues remain regarding the spatial location of mental phenomena and their physical properties. Some philosophers propose that mental phenomena are "constituted" by physical phenomena rather than identical to them.1