Yoruba cosmology, described in foundational studies such as E. Bolaji Idowu's Olodumare: God in Yoruba Belief, holds that Olodumare, the supreme being, is the ultimate source of ase, the generative power by which the world was created and by which it continues to be sustained, and that Olodumare delegated portions of this ase to the orishas at creation, each orisha therefore wielding ase in their own particular domain, Ogun in iron and war, Osun in rivers and fertility, Shango in thunder and justice, and so on. Ase is fundamentally the power to make a thing happen, and this is why it attaches with special force to the spoken word: a properly performed praise-song (oriki), prayer, blessing or curse is understood in Yoruba thought to be genuinely effective, not a symbolic gesture, because the words themselves carry and direct ase toward their object.
Every person, ancestor, animal, plant, and even inanimate object is understood to possess some measure of ase, greatest at the top of the cosmological hierarchy and diminishing but never absent further down, which grounds the Yoruba respect for elders, ancestors and the natural world in a single underlying logic rather than several separate customs. Ritual specialists, especially babalawo, diviners trained in the Ifa oracular corpus, are the primary custodians of the knowledge needed to direct ase correctly, through divination, herbal preparation (oogun) and sacrifice (ebo), work that is described as restoring or redirecting ase that has become blocked or misdirected rather than creating it anew.