  By the essence of a thing William means what is signified by its definition or species name; he often refers to essence as a thing's quiddity (literally, “whatness”), which he identifies with Boethius's notion of quod est or “that which is.” He identifies a thing's being (esse) or existence with Boethius's notion of quo est or “by which it is.”  In the case of a being by participation, its essence and features incidental to its essence are distinct from its being; William describes its being as clothed by them or as what would be left if they were stripped away. Such a being is said to participate in or acquire its being. At times William, following Avicenna, speaks of its being as accidental to it. He terms the being (esse) possessed by a being by participation as being by participation.