Cicero, De Natura, 5, 12; reported in Hoyt's New Cyclopedia Of Practical Quotations (1922), p. 634. Quoted by Bishop Butler. Also used by Richard Hooker, Ecclesiastical Polity, Book I, Chapter VIII., and, Book II, Chapter VII. Found in John Locke, Essays, Book IV, Chapter XV. Also in Hobbes' Leviathan.https://en.wikiquote.org/wiki/Probability