1. Rawls, J. A Theory of Justice. (Harvard University Press, 1971).
2. Berlin, I. Two concepts of liberty. In Four Essays on Liberty. (Oxford University Press, 1969).
3. Marx, K. & Engels, F. The German Ideology. (International Publishers, New York, 1947).
4. Friedman, M., Friedman, R. Free to Choose: A Personal Statement. (Houghton Mifflin Harcourt, 1990).
5. Sen, A. Freedom of choice: concept and content. Eur. Econ. Rev. 32, 269–294 (1988).