Putnam, Hilary (1963a), "Degree of Confirmation" and Inductive Logic. In P.A. Schilpp (ed.), The Philosophy of Rudolf Carnap. La Salle, IL: Open Court, 761-783. pdf

Further Reading:

Putnam, Hilary (1963b), Probability and Confirmation. The Voice of America, Forum Philosophy of Science 10, U.S. Information Agency. Reprinted in Hilary Putnam (1979), Mathematics, Matter and Method. 2nd ed. Cambridge: Cambridge University Press, 293-304. pdf