What textbook was written by the economist who created the "welfare definition" of economics?
Welfare definition of economics: The "welfare definition" of economics is an attempt by Alfred Marshall, a pioneer neoclassical economist, to redefine his field of study. Alfred Marshall: Alfred Marshall (26 July 1842 – 13 July 1924) was one of the most influential economists of his time. Alfred Marshall:  His book, "Principles of Economics" (1890), was the dominant economic textbook in England for many years.
Principles of Economics