An association of algebraic symbols and their properties with those of logic would hardly have been conceivable before the 16th century. Systematic use of letters for numbers in general, and symbols for operations on them, were a development of the 16th and 17th centuries. Although Aristotle's theory of the syllogism used letters of the alphabet for arbitrary general terms, i.e., used variables, there was no formal notion of the composition of terms nor of a negative term, hence no notion of an operation on terms. An early, perhaps the earliest, mention of such an algebraic-like operation occurs in Jacques Bernoulli's Parallelismus ratiocinii logici et algebraici... ¹