“Obelisks, lines of identity, and selfies. Do indexes provide a good account for intuition?”

What is the relationship among an obelisk, a logical tool such as the line of identity in Existential Graphs, and a selfie? For Peirce’s scholars the answer is clear: indexicality, the brute connection between dynamic object and representamen. This brutality of the dual connection, the outward clash, as Peirce used to say, should guarantee that the external non-conceptual world can enter our reasoning and concepts. This is the core of the description of any synthetic reasoning. Some very Kantian questions arise: Is this enough to enable synthetic reasoning? And how can this reasoning work and be reliable? In the Kantian reconstruction, this is the point in which we need intuition. This paper explores the relationship between Peirce’s indexicality and Kant’s intuition. Peirce’s use of the line of identity in Existential Graphs will suggest a remarkable difference in understanding syntheticity between the two authors. Following Peirce’s semiotic notes in Existential Graphs, and the role indexicality plays within it, the paper will propose a broader view of synthetic understanding through special actions called “gestures”.