1. F. S. C. Northrop: The Logic of the Sciences and the Humanities (New York: The Macmillan Company; 1947), p. 146.
2. Pierre Duhem: The Aim and Structure of Physical Theory (Princeton: Princeton University Press; 1954), Part II, Ch. vi, especially pp. 183–90.
3. W. V. O. Quine: From a Logical Point of View (2nd ed.; Cambridge: Harvard University Press; 1961), p. 43. Cf. also p. 41, n. 17.
4. H. Putnam: “Three-Valued Logic,” Philosophical Studies, Vol. VIII (1957), p. 74.
5. R. B. Braithwaite: “Axiomatizing a Scientific System by Axioms in the Form of Identification,” in The Axiomatic Method ed. by L. Henkin, P. Suppes, and A. Tarski (Amsterdam: North Holland Publishing Company; 1959), pp. 429–42.