  In his Mellon lectures presented at the National Gallery in Washington in 1955 (published in 1957), Étienne Gilson classified works of art as Aristotelian substances (for background, see the entries on substance and Aristotle’s metaphysics).  Gilson also claimed that a work has aesthetic and artistic modes of existence in addition to a substantial one. A work exists artistically qua product of the artist’s activity, whereas it exists aesthetically when it is the object of someone’s aesthetic (or contemplative) experience. A similar plurality of modes of existence of works of art had been postulated by Étienne Souriau (1943, 1947), who posited thing-like [chosale], aesthetic, and transcendent modes of existence.