This document discusses functionalism and the inverted spectrum thought experiment. It begins by describing how we can distinguish between different smells, sounds, and textures through our qualitative sensory experiences, known as qualia. It then introduces the inverted spectrum thought experiment, which imagines that two people could have the opposite qualitative experiences of color, such as one experiencing the color we call red as the color the other calls green. The document goes on to explain how functionalism in philosophy of mind argues that what matters is the functional or causal role of mental states, not their intrinsic nature, calling into question whether the inverted spectrum is really possible.