Yale professor Tamar Gendler continues her course Philosophy and the Science of Human Nature with a lecture on John Rawls' A Theory of Justice. She lays out Rawls' claim that justice is the first virtue of social institutions and explains the thought experiment at the heart of his theory, the veil of ignorance, in which rational, self-interested people choose principles of justice without knowing what position they will occupy in society. Gendler walks through the two principles Rawls derives from this setup, the equal liberty principle and the difference principle, and closes by testing the framework against student reactions in the classroom. The lecture runs about 46 minutes and builds on prior sessions about the legitimacy of government, recorded at Yale in spring 2011.