## William Stanley Jevons The Man Of Logic

William Stanley Jevons (1835-1882) — "The Man of Logic"

William Stanley Jevons studied in London at University College after earning enough money while working as at the mint in Australia in his youth. Jevons published many books on the subject of logic and became a professor of political economy, logic, and philosophy. During his career, Jevons also invented a logic machine that could mechanically provide a conclusion from any given set of premises. Although he was a very active man, Jevons died at the early age of forty-seven from a drowning accident.

Starting with Bentham's ideas, Jevons wrote Theory of Political Economy (1871). In his analysis, Jevons accepted the notions that people garnered utility from consuming commodities and that everyone was a rational, calculating, "maximizer" of utility. Therefore, the problem of economics was to study pleasure maximization.

Jevons insisted that value depended entirely on utility and attempted to solve Smith's water-diamond paradox by introducing a concept called "diminishing marginal utility." The concept of marginal utility later became the cornerstone of neoclassical economics. He distinguished between "total utility" (derived from consuming a given quantity of some commodity) from "marginal utility" or "final degree of utility" which was derived from consuming the last small increment of that commodity. After defining the problem (pleasure maximization) and upon distinguishing between relevant terms, Jevons expressed his utilitarian view in mathematical terms using calculus: Total Utility (TU) = f(Q) (total output), and d(TU)/dx = marginal utility (Qx (x)) or the utility derived from the consumption of one more unit of a product or service. Total utility was maximized when marginal utility was equal to zero (i.e. d(TU)/dx = 0; where the slope was equal to zero).

Jevons primarily made two contributions to economic thought: (1) the distinction between total and marginal utility, and (2) to express these in mathematical form. The concept of marginal utility was found to be later very helpful to predict people's consumption choices. It is interesting to note that Jevons also recognized the main limitation of utilitarianism in that it was impossible to make interpersonal comparisons of the relative intensities of utilities because pleasure and pain were based on purely subjective and personal experiences.