1. Karl Popper, Conjectures and Refutations (London: Routledge & Kegan Paul, 1963), p. 241.
2. Carl Gustav Hempel, Philosophy of Natural Science (Englewood Cliffs, N.J.: Prentice-Hall, 1966), p. 44.
3. Karl Popper, The Logic of Scientific Discovery (originally published as Logik der Forschung, 1934) (London: Hutchinson, 1959), pp. 420–441.
4. John E. Cairnes, The Character and Logical Method of Political Economy, 2d ed. (1888; reprint, New York: Augustus M. Kelley, 1965), pp. 129 ff., for the correct distinction between laws and the conditions of their application.
5. Karl Popper, “Rationality and the Status of the Rationality Principle,” in Le fondements philosophiques des systêmes économiques: Text de Jacques Rueff et essays en son honneur (Paris: Payot, 1967); Raymond Boudon, Education, Opportunity, and Social Inequality (New York: John Wiley and Sons, 1974).