From calculemus.org :
The call CALCULEMUS (let's compute) sums up Gottfried Wilhelm Leibniz's (1646-1716) approach to arguments. It encourages those engaged in a dispute to turn arguments into computing. In this enterprise, they may enjoy assistance of a reasoning machine. Leibniz believed that such a machine can be constructed on the basis of a calculating machine, because - anticipating modern logic - he identified reasoning with computing.
From Ilias Kastanas in sci.math (at MathForum.org) (at Google):
His dream was first, a precise symbolic language ("characteristica universalis") to express everything in science 'and philosophy' (it is not clear how wide this was to be) and second, a computational method ("calculus ratiocinator") to resolve statements in that language.
From Historia Matematica:
If controversies were to arise [Leibniz said], "there would be no more need of disputation between two philosophers than between two accountants. For it would suffice to take their pencils in their hands, and say to each other: Let us calculate."