A term is the subject or predicate of a categorical proposition....Let there be assigned to any term its symbolic number, to be used in calculation as the term itself is used in reasoning. I chose numbers whilst writing; in due course I will adapt other signs...For the moment, however, numbers are of the greatest use...because everything is certain and determinate in the case of concepts, as it is in the case of numbers. The one rule for discovering suitable symbolic numbers is this; that when the concept of a given term is composed directly of the concept of two or more other terms, then the symbolic number of the given term should be produced by multiplying together the symbolic numbers of the terms which compose the concept of the given term. In this way we shall be able to discover and prove by our calculus at any rate all the propositions which can be proved without the analysis of what has temporarily been assumed to be prime by means of numbers. We can judge immediately whether propositions presented to us are proved, and that which others could hardly do with the greatest mental labor and good fortune, we can produce with the guidance of symbols alone...As a result of this, we shall be able to show within a century what many thousands of years would hardly have granted to mortals otherwise.

Leibniz, Gottfried. Logical Papers: A Selection, Clarendon Press, Oxford, 1966.