thought of in terms of ordinal utility – that is, it was not necessary to know how much a person valued this or that, only that he preferred X of this to Y of that. Utility was a preference-ordering. With this, Pareto not only inaugurated modern microeconomics, but he also demolished the alliance of economics and utilitarian philosophy (which calls for the greatest good for the greatest number; Pareto said "good" cannot be measured). He replaced it with the notion of Pareto-optimality, the idea that a system is enjoying maximum economic satisfaction when no one can be made better off without making someone else worse off. Pareto optimality is widely used in welfare economics and game theory. A standard theorem is that a perfectly competitive market creates distributions of wealth that are Pareto optimal. Concepts Some economic concepts in current use are based on his work: The Pareto index is a measure of the inequality of income distribution. He argued that in all countries and times, the distribution of income and wealth is highly skewed, with a few holding most of the wealth. He argued that all observed societies follow a regular logarithmic pattern: where N is the number of people with wealth higher than x, and A and m are constants. Over the years, Pareto's Law has proved remarkably close to observed data. The Pareto chart is a special type of histogram, used to view causes of a problem in order of severity from largest to smallest. It is a statistical tool that graphically demonstrates the Pareto principle or the 80–20 rule. Pareto's law concerns the distribution of income. The Pareto distribution is a probability distribution used, among other things, as a mathematical realization of Pareto's law. Ophelimity is a measure of purely economic satisfaction. Major works Cours d'Économie Politique Professé a l'Université de Lausanne (in French), 1896–97. (Vol. I, Vol. II) Les Systèmes Socialistes (in French), 1902. (Vol. I, Vol. II) Manuale di economia politica con una introduzione alla scienza sociale (in Italian), 1906. Trattato di sociologia generale (in Italian), G. Barbéra, Florence, 1916. (Vol. I, Vol. II) (Abridgement of Trattato di sociologia generale) Fatti e teorie (in Italian), 1920. (Collection of previously published articles with an original epilogue) Trasformazione della democrazia (in Italian), 1921. (Collection of previously published articles with an original appendix) English translations The Mind and Society, New York: Harcourt, Brace and Company, 1935 (translation