1. F. P. Kilpatrick, “Problems of Perception in Extreme Situations,” Human Organization, Vol. 16 (Summer 1957), 20–22.
2. Georg W. F. Hegel, Phenomenology of Spirit (New York: Oxford University Press, 1979).
3. Zvi Rosen, Bruno Bauer and Karl Marx: The Influence of Bruno Bauer on Marx’s Thought (The Hague: Nijhoff, 1977).
4. Ludwig Feuerbach, Principles of the Philosophy of the Future (Indianapolis: Hackett Publishers, 1986).
5. Karl Marx, “Economic and Philosophic Manuscripts of 1844,” in Robert C. Tucker, ed., The Marx-Engels Reader, 2nd ed. (New York: W.W. Norton, 1978), 97–98.