Derived from the word holism, itself derived from the Greek word holos, holistic is a term often applied to healing techniques. It refers to the concept first presented by Aristotle in his work, Metaphysics, that "The whole is different from the sum of its parts." In holistic healing techniques, the whole of a person is seen as more than just a collection of individual bones, organs, etc. Humans are seen as complex systems. Holistic healing techniques treat the entire system and not just a single bone or organ. Thus, a person is seen as part of a mental, physical, emotional, and social system, and is treated on all those levels.