- Philosophy.
- (in metaphysics) any of various theories holding that there is only one basic substance or principle as the ground of reality, or that reality consists of a single element.
- (in epistemology) a theory that the object and datum of cognition are identical.
- the reduction of all processes, structures, concepts, etc., to a single governing principle; the theoretical explanation of everything in terms of one principle.
- the conception that there is one causal factor in history; the notion of a single element as primary determinant of behavior, social action, or institutional relations.
- the doctrine that the person consists of only a single substance, or that there is no crucial difference between mental and physical events or properties
- the doctrine that reality consists of an unchanging whole in which change is mere illusion
- the epistemological theory that the object and datum of consciousness are identical
- the attempt to explain anything in terms of one principle only
