|A priori: something that we can know without prior (empirical) investigation. Is the inventory of a priori certainties purely logical? Is a priori knowledge always necessary?|
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A Priori/Wittgenstein: that would have to be a set whose meaning guaranteed its truth - but the meaning requires that we verify the sentence - ((s) verificationism: can then not accept analytic truths).
A Priori/Wittgenstein: expressions that look a priori must be explained - the same expression can be a sentence or a hypothesis - thus, the same expression may be equation or hypothesis - equation: necessary - in visual space, it is a priori that an equilateral triangle is equiangular - you cannot see one without seeing the other - physical space: here not a priori, because the triangle may be inclined.
A Priori/Seeming/Appearing/Wittgenstein: "This chair looks green" here, our certainty is of logical nature and a priori.
A Priori/Necessity/Wittgenstein/Late/Pile: he does not concede the a priori grammatical sentences a form of absolute necessity.
Vorlesungen 1930-35 Frankfurt 1989
Das Blaue Buch - Eine Philosophische Betrachtung Frankfurt 1984
Tractatus Logico Philosophicus Frankfurt/M 1960