Vitalism is the doctrine that life cannot be explained solely by materialism. Often, the non-material element is referred to as the "vital spark" or energy. Some believers in vitalism equate this element with the soul.
Vitalism has a long history in medical philosophies. Most traditional healing practices posited that disease was the result of some imbalance in the vital energies which distinguish living from non-living matter. In the western tradition, these vital forces were identified as the humourss; eastern traditions posited similar forces such as qi, prana, etc.
Aided by the discovery of the microscope, the germ theory of disease, which began to gain momentum in the 16th century, challenged the role of vitalism in western medicine. Attention was also drawn to the role of the various organs of the human anatomy, as opposed to vital forces, in the maintenance of life.
Experiments in the early 19th century continued to erode support for vitalism in the western scientific community. As an implication of vitalism, organic compounds were thought to be only produced by living organisms, as a byproduct of the presence of the vital forces. However, as chemical techniques advanced, it was found that many of these compounds, such as urea, could be produced using the same types of chemical processes that produced inorganic compounds.
Further chemical and anatomical discoveries pushed aside the "vital force" explanation, as more and more life processes came to be described in purely scientific terms, and as the medical model of disease came to be more and more focused on the failure of particular organs and processes in the body.
Vitalism in medicine (and more generally, in society) experienced a resurgence beginning in the late 20th century. Although scientific understanding of the biochemical processes which distinguish living from non-living matter has become increasingly sophisticated, so has the realization that these fundamental processes are incredibly complicated; and no complete, reductionist theory has yet been proposed which coordinates all of the actions which occur in a single cell (let alone a higher organism).
Sometimes a division between soft vitalism and hard vitalism may be drawn. The former have a vitalist world-view but employ common scientific methods in their conduct, stating that their metaphysical ideas have nothing to do with their work. The latter is the category usually identified with vitalism, clearly stating that the living calls for radically different methodologies than dead matter.
In addition, more attention has been directed towards understanding health and the role played by an individual's state of mind. Modern medical vitalism, as represented by such schools as homeopathy, acupuncture, anthroposophy, biodynamic agriculture and chiropractics, tends to emphasize this role in both the cause and treatment of diseases.
In terms of the biology of the cell itself, a return to vitalism may be seen in the philosophy of intelligent design; and the holistic idea that life is an emergent process which cannot be accurately described simply by understanding any number of chemical processes which occur in the cell.