“Nominalism” can refer to a variety of different, albeit related, positions. In most cases, it either refers to the rejection of universals or of abstract objects. What nominalism means for Goodman undergoes two radical changes. In his Ph.D. thesis, A Study of Qualities, he uses the label “nominalist” to describe constructional systems whose constructional basis does not include abstracta, such as Carnap’s system in the Aufbau (Carnap 1928). Whether classes are used in the construction, as Carnap’s Aufbau indeed does, is irrelevant for the characterization of these systems as “nominalist”. Nominalism is not an issue of discussion here; “nominalist” merely occurs as a classification (for more details on constructional systems see  section 4 below.)