  In this section, we present Sylvan’s work in ontology and metaphysics. As discussed below, Sylvan was deeply inspired by Alexius Meinong but, as a matter of terminology, their understanding of ‘ontology’ and ‘metaphysics’ differ: while Meinong would situate metaphysics and ontology as small corners within a more general object theory, Sylvan situated them the other way around. (See, for instance, Meinong 1904, §2 and §11; Sylvan 1995a, 47). In what follows, we follow Sylvan and employ what we take to be contemporary standard usage of ‘ontology’ (roughly understood as the study of what exists and what does not) and ‘metaphysics’ (roughly understood as the study of the structure of reality), while acknowledging that Meinong-scholars might dispute this use of terms. In Section 3.1, we sketch some of the essential features of noneism, that is, Sylvan’s theory about non-existent objects. In Section 3.2, we discuss Sylvan’s attempt at expanding the horizons of traditional ontology by developing a new theory called sistology. Finally, in Section 3.3, we summarize Sylvan’s heterodox account of pluralism, labelled plurallism.