1. Barnard Chester I., The Functions of the Executive (Cambridge: Harvard University Press, 1947), p. 163.
2. Pfiffner John M., Sherwood Frank P., Administrative Organization (Englewood Cliffs, N.J.: Prentice-Hall, 1960), p. 97.
3. Taylor Frederick W., The Principles of Scientific Management (New York: Harper, 1942), p. 10.
4. Michels Roberto, Political Parties, Eden, Paul Cedar (trans.). (Glencoe, Ill.: The Free Press, 1949), p. 69.