In 1968, David Lewis decides that one truth can unify every theory he's had about the nature of the universe. It is the truth that every possible world is equally real. Lewis not only argues for this view, but devises a distinctive way of arguing for it, a method of doing philosophy that is as influential as his views. Meanwhile, a soon-to-be colleague and rival, Saul Kripke, reads Lewis' paper and fires off eight objections, and on the other side of the world, an entire continent becomes enamored with the life and works of David Kellogg Lewis, an admiration that survives to this day. Guest voices include Frank Jackson, Alan Hajek, John Bigelow, Helen Beebe, Anthony Fischer, Peter Anstey, and David Lewis. This episode brought to you by Betterhelp, online therapy and counseling. Get 10% of your first month and support this show by going to betterhelp.com/nation/ This episode is brought you by Scribd, for ebooks, sheet music, podcasts, and magazines. Get a free 60-trial to the entire library at https://try.scribd.com/hiphi To support Hi-Phi Nation, please sign up for Slate Plus at www.slate.com/hiphiplus. Slate Plus members get to listen to every Slate podcast with no ads and bypass the paywall on Slate.com. For a limited time only, you can get $25 off your first year. Learn more about your ad choices. Visit megaphone.fm/adchoices