Today was the first day of the semester at Penn, and I started my course in Global Economic History! The lecture was fun, and I tried to convey not only why economic growth is so important but also that anything we could have done to increase growth over the last 100 years would have had monumental consequences: we would have many more resources to eradicate global poverty, manage the fertility collapse and population aging, clean up the planet and decarbonize the economy, and, more generally, offer better opportunities to everyone across the globe. Artificial intelligence, cheap energy, and modern science and technology have opened the doors to fundamental changes and opportunities, but only if we know how to take advantage of them. The slides are here: sas.upenn.edu/~jesusfv/GEH_1… Nonetheless, I reminded the students of something perhaps even more fundamental. Many of the topics we will cover admit more than one interpretation of the evidence or hinge on how you weigh the outcomes. Does industrial policy work? If it does, is the cost worth paying? I told them many times that they do not have to share my reading of the evidence or my criteria for judging outcomes. I have changed my mind about several of these questions, and experts have a poor record on economic growth over the past century. I also told them we will grade their homework and exams based on command of the material, not on their agreement with me, and that I will try to set questions that agreement cannot answer, but understanding of the material and the arguments presented. John Stuart Mill summarized the reason well: He who knows only his own side of the case, knows little of that…Truth gains more even by the errors of one who, with due study and preparation, thinks for himself, than by the true opinions of those who only hold them because they do not suffer themselves to think. Put another way: I would rather have my students reach the wrong conclusion by their own reasoning than the right one by taking my word for it. After all, independent thinking gave us modern science and technology. Let’s have more of it!