The Scholastics, who accepted Aristotle’s definition, also distinguished primary substance (substantia prima) from secondary substance (substantia secunda): the former is the individual thing — substance properly so called; the latter designates the universal essence or nature as contained in genus and species. And, again, substance is either complete, e.g. man, or incomplete, e.g. the soul; which, though possessing existence in itself, is united with the body to form the specifically complete human being. The principal division; however, is that between material substance (all corporeal things) and spiritual substance, i.e. the soul and the angelic spirits. The latter are often called substantiœ separatœ, to signify that they are separate from matter, i.e. neither actually conjoined with a material organism nor requiring such union as the natural complement of their being (St. Thomas, “Contra Gentes”, II, 91 sqq.).