"A logical graph is a graph representing logical relations iconically, so as to be an aid to logical analysis." ('Logical Tracts. No. 2. On Existential Graphs, Euler's Diagrams, and Logical Algebra', CP 4.420, c. 1903)

"A logical graph is a graph which asserts something, or represents an assertion, concerning a recognized universe, real or fictive." ('Logical Tracts. No. 1. On Existential Graphs', MS 491: 2, c. 1903)

      "Logical Diagram (or Graph): Ger. Logische Figur; Fr. Diagramme logique; Ital. diagramma logico. A diagram composed of dots, lines, &c., in which logical relations are signified by such spatial relations that the necessary consequences of these logical relations are at the same time signified, or can, at least, be made evident by transforming the diagram in certain ways which conventional 'rules' permit." ('Logical Diagram', DPP 2 / CP 4.347, 1902)