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Geometry/rules/experience/Wittgenstein: from the consideration of the rules, the geometry of the cube cannot be derived - the rules do not follow from an act of insight - geometry is not about cubes but about the grammar of the word "cube" - because geometry is not physics - arithmetic: the grammar of numbers - a definition is not proposition about a thing.
Vorlesungen 1930-35 Frankfurt 1989
Das Blaue Buch - Eine Philosophische Betrachtung Frankfurt 1984
Tractatus Logico Philosophicus Frankfurt/M 1960