The main reason for studying the history of economic thought—says Robert Skidelsky in this ninth lecture in INET’s “How and How Not to Do Economics”—is to question the claim that economic knowledge is cumulative. Mainstream economics assumes that all useful economic knowledge from the past is incorporated in present theories. However, the substance and methods of economics have been interminably disputed ever since the start of the “science.” INET sincerely thanks the Julis-Rabinowitz Family for their generous support, who named this series to honor the spirit of a great educator and economic thinker, Uwe Reinhardt. For nearly 50 years, the late Uwe Reinhardt was a beloved economist and professor at Princeton University. Known best for helping to shape critical discourse around healthcare markets, his biting wit and intellect challenged students, colleagues, and policymakers alike to follow the data and to check all assumptions at the door. INET also thanks Rethinking Economics for their voices and contributions.