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Mathematics/Wittgenstein: mathematical propositions are not true or false. - But they show what is meaningful and what senseless.
Sense/senseless/nonsense/color/numbers/number/Wittgenstein: E.g. A sentence like red is darker than pink does not exist, because there is no sentence that denies it. - One does not speak here of a property of the Red, but of the grammar of the word red. - Similarly: E.g. it is a property of the number 1, that it belongs to a lecturer in this room and it is a property of 1, that 1 < 2.
Senseless/nonsense/Mathematics/assignment/Wittgenstein: if there is no criterion specified for an assignment, it is senseless to attempt the assignment. - E.g. it is senseless to say that there is no test for the orbit of the comet, because people do not live long enough.
Vorlesungen 1930-35 Frankfurt 1989
Das Blaue Buch - Eine Philosophische Betrachtung Frankfurt 1984
Tractatus Logico Philosophicus Frankfurt/M 1960