The concept of Anima Mundi (or World Soul) pervading all of nature is so old that its origins are very obscure. Yeats has kept developing his own philosophy (or system) regarding this Anima Mundi for his art and belief all his life. In this article, I try to treat Yeats's theoretical statements on the Anima Mundi which can be easily found in his essay "Anima Mundi" in Per Amica Silentia Lunae (1918), one of the greatest watershed document in his theory of the Anima Mundi, the
poet's ultimate expression of his belief.
Like many of ancient western and eastern mysterious religions, Yeats no longer distinguishes between the great memory of Anima Mundi and the minds and memories of its occupants. Also he reaffirms the four elements as integral to the World Soul concept. He assigns elemental attributes to the images glimpsed in visions, creating a fourfold model of perception. This short but important essay constitutes the outstanding feature of Yeats's newly evolved concept, the Anima Mundi is not merely a place, a shadowy subliminal Hades. It is a congeries of souls, of discarnate intelligences whose multifarious activities range from regulating nature's cycles to potential anamnesis.