Soumaya Keynes of The Economist and PIIE Senior Fellow Chad P. Bown have a wide-ranging conversation with Dani Rodrik (Harvard Kennedy School) about trade agreements. In Part 4 of this 4-episode conversation, they provide a “bonus” technical discussion about the state of formal economics research into the purpose of trade agreements. This includes how governments use cooperative trade deals to both stop the spread of international externalities and to tie their own hands with respect to special interests.