2.7 THE IDEA OF A GRAPH

Llull connected his "basic concepts" with lines, and prescribed that the lines had to be followed to combine the concepts and derive the consequences. This was new. Not now, though; we have a name for the device Llull invented: we call it a graph. The two amazing things about this are, first, that Llull gave a dual isomorphic variety of it: he compiled the graph's information in the form of a two-entry table (just what we term the adjacency matrix of the graph) and, second, that Llull's graphs were not meant as mere concept-structuring or taxonomic (tree-structured concepts were available since late Roman times) but were conceived rather as a present-day's "semantic network" and intended to be "followed", i.e. dynamically executed as though it were a truly fact-finding "program" or a decision tree (as in AI) in a decision procedure.