1. Paul Oppenheim and Hilary Putnam, ?Unity of Science as a Working Hypothesis?, Minnesota Studies in the Philosophy of Science, Vol. II (ed. by Herbert Feigl, Michael Scriven, and Grover Maxwell), University of Minnesota Press, Minneapolis, 1958, pp. 3?36.
2. Robert L. Causey, ?Complications in the Unification of Science?, a paper read at the meeting of the Philosophy of Science Association in Pittsburgh, October, 1968.
3. Patrick Suppes and Joseph L. Zinnes, ?Basic Measurement Theory?, Handbook of Mathematical Psychology, Vol. I (ed. by R. Duncan Luce, Robert R. Bush, and Eugene Galanter), John Wiley and Sons, New York, 1963, pp. 1?76.
4. Robert L. Causey, ?Polanyi on Structure and Reduction?, Synthese 20 (1969), 230?237.
5. Ernest Nagel, The Structure of Science, Harcourt, Brace & World, New York, 1961, pp. 336?366.