n. in philosophy and metaphysics, actuality or realization as opposed to potentiality. Aristotle used the word to refer to the soul (psyche), seen as that form within the material being by virtue of which it achieves the actuality of its nature (see actual). Later philosophers employed the term in a similar vein. Gottfried Wilhelm Leibniz referred to monads as being entelechy, or having entelechy, defined as the power to perfect their given nature (see nisus). In certain vitalist philosophies and theories, entelechy refers to the vital force within an organism that allows for life, development, and self-fulfillment (see élan vital; vitalism).