The essence of this book can be distilled into a graph whose nodes are universes, and whose edges are specific types of referential relations. This graph is displayed below, using symbols from Section 1, “Mathematical Symbols”:
The arrows in this diagram show the typical direction of causal flow between the universes. These universes, however, also reference one another. Although there are several referential relationships between the universes, there are two which are essential: concepts reference percepts, and percepts reference objects. This is shown (without depicting the individual parts in each universe) in the diagram below:
References do not map all of the world into perception: some things are not perceived. For any individual, there is a part of the physical universe which is not present in the subjective universe. Similarly, there is a part of the subjective universe which is not mapped into the conceptual universe. These left-over parts are depicted as nodes on the left in the diagram below:
This diagram is a part hierarchy where the nodes are formed by dividing the parent node. We will refer to the nodes of this diagram as follows:
U: The Physical Universe
U-O: The Objective Domain
O: The Subjective Universe
O-U: The Perceptual Domain
V: The Conceptual Universe
The nodes on the right branch of this tree contain references to the larger whole, in virtue of which they are called referential universes. Universes are formed by reference: for example, the subjective universe contains references to the physical universe, whereas the objective domain does not.
If we focus on the terminal nodes of this meronomy, we see that the universe can be composed of three distinct domains: the objective domain, the perceptual domain, and the conceptual domain. The fact that these are exclusive of one another is leveraged when the distinction is important, such as when classifying the parts of a universe. For example, when we refer to parts of the physical universe, we are often referring only to those parts which are not parts of the subjective universe: hence, they are called objects instead of percepts. The parts of the physical, subjective, and conceptual universes can be depicted as follows: