What do we know and what do we not know? Our known data and our unknown data.
Unknown quantities taken as known quantities. Matter and motion. What does
positivist philosophy arrive at? Identity of the unknown quantities: x = y, y = x. What
do we actually know? The existence of consciousness in us and of the world outside
us. Dualism or monism? Subjective and objective cognition. Where do the causes of
sensations lie? Kant's system. Time and space. Mach's observation. What the physicist
actually works with.