In philosophy of mind, qualia (/ˈkwɑːliə/ or /ˈkweɪliə/; singular form: quale) are defined as individual instances of subjective, conscious experience. The inverted spectrum thought experiment, originally developed by John Locke, invites us to imagine that we wake up one morning and find that for some unknown reason all the colors in the world have been inverted, i.e. swapped to the hue on the opposite side of a color wheel.