How does functionalism use the causes and effects of pain to identify it?

In the philosophy of mind, functionalism defines mental states, such as pain, by their specific causal roles rather than their internal physical composition.

Under this framework, pain is identified through a network of relationships involving three primary components:

• Inputs: The sensory stimulations that cause the state, such as physical trauma like cuts or burns.1
• Internal States: The subsequent mental states triggered by the initial input, such as feelings of fear.1
• Outputs: The resulting behaviors, often referred to as "pain behaviour," such as saying "ouch".1

By defining pain through these causal connections, functionalism posits that the state is not tied to a single physical substance. Instead, it is "multiply realizable," meaning the same functional role—the same pattern of causes and effects—can be performed by different physical systems, whether they are human, animal, or potentially artificial.1