Reality+: Virtual Worlds and the Problems of Philosophy by David J. Chalmers (W. W. Norton & Company, 2022).

Some philosophers are purists, thinking that the problems of philosophy float above the world of changing empirical circumstances. In Reality+, David Chalmers demonstrates the untenability of this purism by showing that technology raises new philosophical questions and changes old ones. The book is also successful as a relatively accessible, entertaining, and not entirely Eurocentric introduction to the problems of philosophy. It is a sprawlingwork coveringmany different topics, and a kind of manifesto which argues for Chalmers’s sometimes controversial views, some of which are developed more fully in his earlier work, and which together form a general approach to reality in a technological age. Most strikingly, he proposes a ‘structuralist’ account of reality that can solve the traditional problem of global skepticism about the external world. This claim is the central, recurring theme of the book that holds the disparate parts together. Unsurprisingly, since it targets one of philosophy’s enduring problems, it the most philosophically problematic claim in the book. According to Chalmers, you and theworld you seemaywell be part of a simulation – he thinks that there is at least a 25% chance of this (p. 101). His reasoning for this surprising estimate resembles Bostrom (2003)1, but goes beyond it in some details. Throughout the history of the universe, there will probably be many advanced civilizations with the technology to create trillions of detailed simulations containing ‘sims,’ or simulated beings that resemble you. And some of these civilizations are enough like ours in their needs and interests to want to do so (pp. 90, 138-39). Of course, some may not bother. But if even one out of a million such civilizations does so, that one could well create trillions of sims, which would vastly outnumber the non-sims in the universe. Accordingly, you’re probably a sim because most conscious beings in the universe are (Ch. 5). A crucial step is his argument is that simulated beings can be conscious, just like you. His argument for this, though, could have used more discussion, and objections to it considered more fully. Still, one need not agree with all of Chalmers’s arguments (nor his estimate of the chances) to appreciate the main upshot: the simulation scenario is a real possibility. The closer our technology gets to producing a