 While this entry is about mass and count expressions, the literature has typically focused instead on what are called mass and count nouns. Mass nouns include nitrogen, porridge, trash, china, traffic, data, shade, music, pain, and furniture. Count nouns include horse, futon, army, codicil, proposition, and galaxy. It should be noted from the outset that the relation between the mass/count distinction and the stuff/thing distinction across all metaphysical categories is not straightforward, as there are so many different kinds of entities (e.g., events, concreta, sets, processes, absences, conventional entities, etc.) referred to by both mass and count expressions.