Robert M. Pirsig, author of Zen and the Art of Motorcycle Maintenance and Lila: An Inquiry Into Morals, died today at the age of 88, according to a statement released by his publisher. Pirsig’s work explored a system of thought called the “Metaphysics of Quality,” which has been defined as “a thesis that quality is the basis of reality, and that this understanding unifies most East Asian and Western thought.”