Adam Smith wrote in 1776 that no human wisdom or knowledge could ever be sufficient to direct the industry of a nation. A century and a half later, other men turned that sentence into a formal argument. Carl Menger argued in 1871 that value sits in the person valuing, not in the object. Ludwig von Mises argued in 1920 that without private ownership of producer goods there are no exchange ratios for them, and so no way to weigh one use of a ton of steel against another.