Since the characteristica universalis is diagrammatic and employs pictograms, the diagrams in Leibniz's work warrant close study - wikipedia 
On at least two occasions, Leibniz illustrated his philosophical reasoning with diagrams. One diagram, the frontispiece to his 1666 De Arte Combinatoria, represents the Aristotelian theory of how all material things are formed from combinations of the elements earth, water, air, and fire.
Diagrammatic reasoning. Diagrammatic reasoning is reasoning by means of visual representations. The study of diagrammatic reasoning is about the understanding of concepts and ideas, visualized with the use of diagrams and imagery instead of by linguistic or algebraic means. - wikimedia
Jaakko Hintikka. Kaarlo Jaakko Juhani Hintikka was a Finnish philosopher and logician. Hintikka is regarded as the founder of formal epistemic logic and of game semantics for logic. - wikimedia