Although the harm principle as introduced in the last lecture seems straightforward at first glance, today Professor Shapiro discusses its ambiguities. If it "must be calculated to produce evil to someone else," who will be doing the calculations? Second, what does "calculated" mean? Does committing harm imply mens rea, or should strict liability be observed? The class discusses such issues as prostitution, free trade, same-sex marriage, statutory rape, Good Samaritan laws, marital rape, discrimination, and tort adjudication (specifically the 1950s case on thalidomide). Professor Shapiro concludes that in calculating harm, one must make political choices, which places the Enlightenment ideal of replacing politics with science in jeopardy.