Organicism is a philosophical orientation that asserts reality is best understood as an organic whole. It is also a biological doctrine that stresses the organization rather than the composition of organisms.
As a doctrine it rejects mechanism and reductionism, the doctrines that claim the smallest parts by themselves explain the behavior of larger organized systems of which they are a part. However, organicism also rejects vitalism, the doctrine that there is a vital force different from physical forces that accounts for living things.
A number of biologists in the early to mid-twentieth century embraced organicism. They wished to reject earlier vitalisms but to stress that whole organism biology was not fully explainable by atomic mechanism. The larger organization of an organic system has features that must be taken into account to explain its behavior.
Organicism is distinguished from holism to avoid what is seen as the vitalistic of spritualistic connotations of holism. Holism contains a continuum of degrees of top-down control of an organization. With holism there is monism, the doctrine that the only complete object is the whole universe, or that there is only one entity, the universe. Organicism allows relatively more independence of the parts from the whole, despite the whole being more than the sum of the parts, or the whole exerting some control on the behavior of the parts.
More independence is present in relational holism. This doctrine does not assert top-down control of the whole over its parts, but does claim that the relations of the parts are essential to explanation of behavior of the system. Aristotle and early modern philosophers and scientists tended to describe reality as made of substances and their qualities, and to neglect relations. Twentieth century philosophy has been characterized by the introduction of and emphasis on the importance of relations,whether in symbolic logic or in metaphysics.
Organicism has some intellectually and politically controversial associations. Holism, the doctrine that the whole is more than the sum of its parts, is often used synonymously with organicism or as a broader category under which organicism falls, and has been coopted in recent decades by holistic medicine and by New Age Thought.
It has also been used to characterize notions put forth by various late 19th-century social scientists who considered human society to be analogous to an organism, and individual humans to be analogous to the cells of an organism.