Could Gresham's Law, declaring that bad money drives out good, apply as well to public discourse? "Capital in the Twenty-First Century," a neo-Marxist polemic by a young Frenchman, was recently the object of inordinate acclaim—until its key "income inequality" research was discredited by serious economists. Meanwhile, a true gem of a book about economic principles and wayward policy runs the danger of being lost in relative obscurity.

"Money," by Steve Forbes and his co-author, Elizabeth Ames,...