M. Schlick, in R. Rorty (ed.),

The Linguistic Turn (Chicago: University of Chicago

Reconsidering Logical Positivism (Cambridge: Cambridge University Press, 1999), p. 29.

B. Bolzano,

Grundlegung der Logik (Hamburg: Meiner, 1963), p. 66.

I. Kant,

Critique of Pure Reason,

B p. 172, A p. 133.

E. Husserl,

Gesammelte Schriften,

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