• Principles of Economics (1890): economics is "a study of mankind in the ordinary business of life" — that part of individual and social action most closely connected with the attainment and use of the material requisites of well-being.
• Merit: restored the human being to the centre; distinguished wealth as means, welfare as end; made economics a social, not merely commercial, science.
• Critique (Robbins' attack): "welfare" is unmeasurable and vague; some welfare (services of teachers, lawyers, doctors) is immaterial yet economic; and some material things (cigarettes) reduce welfare but remain economic goods. Marshall also kept economics normative (ethics in), which Robbins rejected.