Understanding Propositional Logic William Stanley Jevons (1.09.1835–13.08.1882) was an English economist and logician known for his pioneering works on political and mathematical economics, including the theory of utility As well as contributing to the early development of modern logic, in 1869 he designed one of the first mechanical computers which he called the logic piano Jevons studied natural sciences and moral philosophy at the University College of London and, in 1866, was appointed Professor of Logic, Mental and Moral Philosophy and Professor of Political Economy at Owens College His book A General Mathematical Theory of Political Economy (1862) is one of the first works on mathematical methods in economics which, being concerned with quantities, he regarded as an essentially mathematical science Jevons’ most important work on scientific methods is his Principles of Science (1874) In 1870 he published Elementary Lessons on Logic, which soon became the most widely read elementary textbook on logic in the English language, later supplemented by his Studies in Deductive Logic Jevons developed a general theory of induction, which he regarded as an inverse method of deduction; he also developed and published his own treatments of Boole’s approach to logic and on the general theory of probability, and studied the relation between probability and induction 27