# HOW TO THINK ABOUT MENTAL QUALITIES David Rosenthal **Opening (not a real abstract):** I. Intuitions about Mental Qualities It’s often held that undetectable inversion of mental qualities is, if not possible, at least conceivable. It’s thought to be conceivable that the mental quality your visual states exhibit when you see something red in standard conditions is literally of the same type as the mental quality my visual states exhibit when I see something green in such circumstances. It’s thought, moreover, to be conceivable that such inversion of mental qualities could be wholly undetectable by any third-person means. And since first- person access is limited to a single individual, and so could not reveal a disparity in mental quality between us, third-person undetectability means undetectability tout court. There is an extensive literature about whether such inversion is conceivable, and whether it’s even possible. But my concern here will not **Authors:** [[David Rosenthal]]