What is it? That's the Question!

The ti esti question "What is it?" is the central question of the philosophy of Socrates and Plato.  But how to understand this question?

Plato presents a dichotomic vision of answering the question What is it? On the one hand, an extensional approach, which he condemns, on the other hand an intensional approach, which he favors. A typical example of these contrasting ways to deal with the ti esti question can be presented through the case of the notion of prime number. One can reply extensionally to the question “What is a prime number?” by an enumeration: “2, 3, 5, 7, 11 …” or intensionally by “a natural number greater than 1, that can be divided only by 1 and itself”.  Enumeration does not give any understanding and can lead us to sleep faster than pineapple juice  … But everything is not so cool as mathematics! If we turn to a natural entity like a cat, or an artificial entity, like a car, there are no obvious intensional answers. 

In the International  Congress "What is it?  That's the Question!"  that will take place in Rio de Janeiro, Brazil, July 27-31, 2026, we will have on the one hand talks about the history of the question, on the other hand talks about specific topics, for important Xs ... But the idea is to have in these specific talks a good equilibrium between the X in question and the general methodology to answer the ti esti question, in the line of the recent paper "What is money?" (Jean-Yves Beziau & Flawê de Lara Bone), Logica Univeralis, 19 (2025), pp.237-272.