The classical economists regarded minimum profits as an element in cost of production, 115. — Walker's rent theory, 118. — Similar views by other Americans, 119. — By Europeans, 121. — Profits regarded as wages of labor by still others, 123. — Distinction needed between earned efficiency profits and unearned scarcity profits, 127. — Efficiency profits recognized by the law, 128. — Patents, trade secrets, invention, 129. — Judgment and risk-taking, 133. — Surplus or scarcity profits differ from efficiency profits, 134. — Are not an element of cost, 135. — Defects of the labor theory, 136.