Importance: The book built on ordinal utility and mainstreamed the now-standard distinction between the substitution effect and the income effect for an individual in demand theory in the 2-good case. It generalized analysis to the case of one good and all other goods, that is, the composite good . It aggregated individuals and businesses through demand and supply across the economy. It anticipated the aggregation problem , most acutely for the stock of capital goods. It introduced general equilibrium theory to an English-speaking audience, refined the theory, and for the first time attempted a rigorous statement of stability conditions for general equilibrium.