Artificial general intelligence is the rare technical term that everyone uses and no one defines. It anchors company mission statements, doom forecasts, government strategies and trillion-dollar valuations, while meaning something different in nearly every sentence it appears in. Julian Togelius's Artificial General Intelligence, a slim entry in the MIT Press Essential Knowledge series, performs a service the discourse badly needed: it takes the term apart, examines the pieces, and asks whether they were ever designed to fit together.