Husband and wife philosophers from Princeton, Stephanie Lewis and David Lewis gave two lectures.  Ms. Lewis lectured on the proposition, "When Legitimate Rule is in Doubt, So is Legal Validity," and Mr. Lewis asked his audience to consider the question, "Could a Time Traveler Change the Past?"  The couple collaborated on the influential article, “Holes,” published in the Australasian Journal of Philosophy in 1970. Taking the form of a dialogue between “Argle” and “Bargle,” the essay explored the range of metaphysical issues raised by the concept of a hole.