Der Operationskreis des Logikkalkus

Ernst Schröder's Der Operationskreis des Logikkalkuls (1877), meaning "The Circle of Operations of the Logical Calculus," was an early work in algebraic logic. It was influenced by Boole and Grassmann but presented with exceptional clarity. Schröder's approach was "intensional," meaning the letters in his calculus represented concepts rather than classes or things. He distinguished this from numerical algebra, stating that in his logic, letters represented "arbitrary concepts".12

This work was a precursor to his more extensive three-volume Vorlesungen über die Algebra der Logik (Lectures on the Algebra of Logic). Schröder's contributions were significant in the development of symbolic logic and influenced later logicians in Germany. The term "operational calculus" itself refers to a branch of mathematics that applies algebraic operations to symbols of operation as well as magnitude.123