Concept developed by Leibniz, in whose philosophy monads are the true unities and hence the only true substances. Monads are extensionless, mental entities, capable of perceptions and appetitive states, but each of them self-sufficient and developing without relation to any other (see pre-established harmony ). Their self-sufficiency is often registered by calling them ‘windowless’ monads. The foundation of the doctrine is that relations must ultimately be explained by the categorical, non-relational nature of things. See also Conway.
Philosophy dictionary. Academic. 2011.