1. Bateson, G., (1972), Steps to an Ecology of Mind, Ballantine Books, New York.
2. Campbell N.R.,(1957), Foundations of Science. The Philosophy of Theory and Experiment (Formerly Physics: The Elements), Dover, New York.
3. Churchman C. W.,(1971), The Design of Inquiring Systems, Basic Books, New York.
4. Elliot R., (1991), Environmental Ethics, in: A Companion to Ethics, Edited by Peter Singer, Oxford, Eng., Blackwell.
5. Ferrater Mora, J., (1979), Diccionario de Filosofia, Alianza Editorial, Madrid, Spain. In Spanish. Four Volumes, Vol. II, 1633.