1. Bryce, J. (1888) The American Commonwealth, London: Macmillan.
2. Carnap, R. (1928) Der Logische Aufbau der Welt, Leipzig: Felix Meiner Verlag.
3. Catlin, G.E.G. (1927) The Science and Method of Politics, New York: Knopf.
4. Crick, B. (1959) The American Science of Politics, Berkeley: University of California Press.
5. Dahl, R. (1956) A Preface to Democratic Theory, Chicago: University of Chicago Press.