The metaphysical doctrine that the functions and processes of life are due to a vital principle distinct from physicochemical forces and that the laws of physics and chemistry alone cannot explain life functions and processes. Vitalism is opposed to mechanistic materialism. The belief was that matter was divided into two classes based on behavior with respect to heat: organic and inorganic. Inorganic material could be melted but could always be recovered by removing the heat source. Organic compounds changed form upon heating and could not be recovered by removing the heat source. The proposed explanation for the difference between organic and inorganic compounds was the Vitalism Theory, which stated that inorganic materials did not contain the "vital force" of life.