The plan is to address the title question by examining various approaches to one long-standing philosophical conundrum, the problem of radical skepticism: how do we manage to know anything at all about the world around us? This looks like a silly question, with obvious answers, until we’re struck by the familiar and unsettling thought, ‘how do I know I’m not just dreaming all this?’ That thought can make the question seem unanswerable.  How and why this is so will be the focus of the first lecture.