How did Gottfried Wilhelm Leibniz’s symbolic logic resemble George Boole’s later system?

Gottfried Wilhelm Leibniz’s symbolic logic, developed in the 1680s, bears a remarkable resemblance to the symbolic logic system introduced by George Boole in 1847. Both systems utilize an equational, algebraic approach to represent logical relationships.12

Key similarities include:

• Algebraic Structure: Leibniz employed symbols to represent concepts and used algebraic operations to manipulate them, similar to how Boole later formalized Boolean algebra.12
• Logical Operations: Leibniz used notation analogous to addition and multiplication to combine concepts. For instance, he used a symbol similar to addition ($\oplus$) to signify that concepts in A and B constitute C, and juxtaposition (e.g., $AB$) to signify the intersection of concepts, mirroring modern logical operators.12
• Calculus of Reason: Both envisioned logic as a calculus ratiocinator—a system where reasoning could be performed mechanically or algorithmically, much like arithmetic.12

Despite these parallels, Leibniz’s system was "intensional," focusing on properties or concepts, whereas Boole’s system is often applied to "extensional" logic. Furthermore, Leibniz’s work remained largely unpublished until 1903, meaning it had virtually no influence on the development of Boole’s system.12