How empirical was Adam Smith's The Wealth of Nations?
That is, how much empirical research does it contain?
I want to understand whether books that are regarded as "standards" in political science and economics are actually "scientific" in the sense that they contain empirical proof for the theses that they put forward.
Empirical research is more valid than philosophical, when the theses deal with things that are claimed to exist in other ways than mere beliefs. Empirical research (in the humanities) thus means validating theses through studying how people actually behave or formulating theses based on observing people.