Do we learn everything we know from the world around us, or are there some things we learn independently of our sensory experiences? Rationalists argue that some of our knowledge, like concepts in algebra and trigonometry, is innate or intuitive. We know that two plus two equals four independently of our specific observations of the world around us. Empiricists argue that all knowledge comes from experience, and that even basic principles of mathematics would be unknowable to us if it weren’t for our interactions with the external world. In this episode we provide an overview of both positions and talk about philosophers who have lined up on both sides of the debate. We also provide a complete guide to casting an action adventure movie about British Empiricism and Continental Rationalism (spoiler alert: John Locke is portrayed by Adrien Brody). We answer some listener mail about fax machines and personal identity, and unlock the secret of Mark’s favorite doughnut (spoiler alert: it’s the Bear Claw).