"Diagrams are massively used in many reasoning processes and in the very practice of science; however, there is in general no consensus about the reasons why a diagram can be successfully used, and whether it represents only an auxiliary aid for reasoning or is something more fundamental for it. The aim of the present project is the in depth investigation into the capacity of diagrams to convey information and supporting reasoning and inferences, which is necessary for a general evaluation of the tools available for thought, especially in view of the very fast developing of new technologies that support reasoning and communication. The objectives of the current project are the following: (1) the evaluation of the cognitive advantages in the use of diagrams. (2) a classification of diagrams. To assess this question, three hypotheses will be tested empirically: (a) diagrams confer cognitive advantage over linguistic representations. It will be evaluated to what extent diagrams are effective in promoting inference generation, in particular in making it possible to extract and manipulate information without long calculations. (b) diagrams constitute a cognitive advantage over mental computations, for the very reason that they are extra-mental devices. It will be evaluated whether the claim that certain cognitive problems are solved more quickly, easily and reliably by performing actions and manipulations directly on the diagram itself to promote new inferences is true. (c) it is necessary to move from the question of what a diagram is to the question of what a diagram is used for, and to focus on the different uses that can be made of diagrams to convey information. The cognitive study into the use of diagrams is thus combined with a pragmatic study of the way diagrams are actually used, thereby side-stepping the uninformative dichotomy visual vs. non visual."