In July’s Adam Smith 300 essay for Capital Matters, George Mason University economics professor Don Boudreaux writes about Smith’s presumption for unilateral free trade:
Smith was not a free-trade absolutist. He explicitly identified four possible justifications for government to impose tariffs on imports. Upon discovering this fact, protectionists often trumpet it as if it’s news to economists who support free trade. It’s not. That Smith made these exceptions has been known since the first copies of the Wealth of Nations found their way into readers’ hands nearly 250 years ago. I myself learned about them more than 40 years ago in an undergraduate course on the history of economic thought.
The exceptions identified by Smith, however, are only that: exceptions. If the goal is to economically enrich the masses as much as possible, unilateral free trade should be presumed to be the best policy. The burden of proof is on protectionists to justify government-erected obstacles and not on free traders to justify keeping commerce free.
Read about each of the four exceptions, and what Smith thought about tariffs as tax policy, here.