Henology (from Greek ἕν hen, "one") refers to the philosophical account or discourse on "The One" that appears most notably in the philosophy of Plotinus. Reiner Schürmann describes it as a "metaphysics of radical transcendence" that extends beyond being and intellection. It can be contrasted with ontology, as ontology is "an account of being" whereas henology is an "account of unity."
Henology stands in contradistinction to several other philosophical disciplines. The term "henology" refers to the discipline that centers around The One, as in the philosophies of Plato and Plotinus. It is sometimes used in contradistinction to disciplines that treats Being as its starting point (as in Aristotle and Avicenna) and also to those that seek to understand Knowledge and Truth (as in Kant and Descartes).