Although my questions about reality originated from teaching accounting, the book is not an accounting ontology or, as one might say nowadays, ‘a domain ontology of accounting’. It is rather concerned with general ontological questions – that is to say, with the general framework for exploring issues about reality. To create a domain ontology of accounting would ﬁrst require a clear view of the general ontology underlying it – though steps toward such an accounting domain ontology have been undertaken in the publications by MacCarthy (1982, 2005), Geerts and MacCarthy (1992, 1996, 1999, 2002), and others (for details, see Chapter 11). Nevertheless, several chapters of the present book discuss ontological questions that arose from teaching accounting theory (see Chapters 2 to 5), though without being necessarily unique to this subject matter. I have tried to present a string of ontological inquiries and explorations designed to clarify the notion of reality and what is behind it. The reference to accounting and other economic disciplines indicates the origin of this inquiry rather than a limitation to scope. Although dealing primarily with questions of general ontology, I do not believe – contrary to many ontologists – that the question ‘what is real?’ should constitute the primary focus. In the course of these inquiries I have come to the conclusion that the central question of ontology ought to be: ‘in what sense is something real?’. This implies that reality is structured, and that there exist different kinds of realities. Hence, it is crucial to identify the type of reality under question. Is it physical, biological, or social-cultural reality? Is it past, present ,or future reality? Is it autonomous or non-autonomous reality? Is it necessary, probable, or possible reality? Is it concrete or abstract reality? As the term ‘existence’ (the central notion of any ontology) may apply to all of these manifestations, there arises the question whether these are merely different aspects of a single reality. Or are we, indeed, justiﬁed in talking about different realities? I believe we are justiﬁed in accepting such a plurality because, after all, not all of those manifestations apply simultaneously to a speciﬁc reality. Obviously, the property of being alive applies only to biological but not to physical reality. But that does not contradict the fact that all of these realities have a common origin.