  Mach perhaps writes more about space than any single other topic; the Analysis of Sensations is dominated by discussions about it (Chapters 6 to 10 are devoted, more or less, exclusively to it) as is Space and Geometry. His Science of Mechanics contains his famous analysis of absolute space.  The starting point of Mach’s thought is that physiological space is different from geometrical space. The idea of physiological space was not new with Mach; apparently initiated by Müller, it was discussed by both Helmholtz and Hering.  Physiological space is the space constructed by our cognitive structure. It is not something we intentionally create, but rather it is a product of unconscious adaptation, and as such, may be a source of a priori truths. Geometrical space, on the other hand, is an intellectual construction, “reached for the most part by purposeful experience.” [SG: 5] While physiological space is completely psychological, geometrical space is an abstraction on physiological space. Neither is an ‘objective’ or ‘absolute’ space.