²²I am here referring to the common, non-technical definition of relativity, such as “the state of being dependent for existence on or determined in nature, value, or quality by relation to something else” (Merriam-Webster.com, accessed 24/1/2022). The interpretation of emptiness as relativity was initiated by Theodore Stcherbatsky, one of the earliest Western interpreters of Buddhist philosophy. Some commentators may prefer ontological interpretations of emptiness, but my treatment here sees it more as an epistemological quality, compatible with my computational approach. Emptiness actually has two different but related well-known definitions in Mahayana Buddhism (Williams, 2008b). First, there is the Yogācāra definition based on the “consciousness-only” thinking described in Chapter 12: All phenomena in the world are called empty because they are simply phenomena in the mind and constructed by the mind; in particular, any categories and concepts are merely mental constructs. This is rather similar to what we just discussed, except that in Yogācāra, such thinking can even be taken to a metaphysical level, denying the existence of the outside world—at least in some interpretations. Second, there is the Madhyamaka definition, where all phenomena are called empty in the sense that they are simply products of long causal chains, thus lacking any independent, intrinsic existence, and subject to change at any time. This is a very general definition that is ultimately supposed to contain most related properties described in this book or other Buddhist schools; it is surprisingly similar to the dictionary definition of relativity just given. For example, subjectivity of perception can be seen as a result of such causality because perception is causally influenced by the priors in the perceiver’s brain, and thus the percept does not exist independently (of the brain).