How did functionalism oppose psychophysical reductionism?

Hilary Putnam’s functionalism opposed psychophysical reductionism by arguing that mental states are defined by their functional or causal roles rather than by their specific material composition.1

The core of this opposition lies in the thesis of multiple realizability. Putnam observed that the same mental function can be performed by different physical systems—much like how the same software can run on different computer hardware. Because a single function can be realized in various physical structures, mental properties cannot be uniquely or exclusively reduced to specific physical properties or neurophysiological states.123

By characterizing the mind through its functional organization rather than its substance, functionalism allowed for a complex level of psychological explanation that is not straightforwardly reducible to physics or neurophysiology. This approach successfully avoided the "chauvinistic" commitment of type-identity theories, which insisted that mental states must be identical to specific human brain states, while simultaneously avoiding the postulation of nonphysical entities.3