Why “What is it?” ?

1. Flawé: How did you begin to take an interest in the question “What is it?” (ti esti)?

JYB:  My interest did not begin directly with that question, but with Plato, already in high school. Later, at the Sorbonne, during my undergraduate studies, I took two memorable courses on the philosopher: one with Sarah Kofman, on Mimesis in Plato, and another with Monique Vallon-Basset on the dialogue Sophist. It was during that period that the Platonic question began, for me, to acquire a special prominence.

I also read Heidegger’s essay “Plato’s Doctrine of Truth” in which he shows that, in the allegory of the cave, two different conceptions of truth coexist: on the one hand, truth as unconcealment (aletheia); on the other hand, truth as correspondence. This led me, in 1988, to undertake a master’s degree on the allegory of the cave under Sarah Kofman’s supervision.

Then, influenced by Plato himself and by the famous motto that, according to tradition, stood at the entrance of the Academy—“Let no one  ignorant of geometry enter”—I decided to concentrate on the study and practice of mathematics. I then completed a master’s degree (1990) and a doctorate (1995) in mathematical logic in the Department of Mathematics at Paris 7 University, one of the great world centers in the field. My supervisor was Daniel Andler, who had earned his doctorate in mathematical logic at Berkeley in California, in Tarski’s famous school. In my dissertation, I managed to prove a nontrivial theorem—which, according to the criterion of the great mathematician André Weil (father of Bourbaki), is the mark of a true mathematician.

The subject of my doctorate was universal logic, an idea that I myself proposed and that later led me to create the journal Logica Universalis, launched by Springer in 2007 (today one of the best logic journals in the world), and also the global UNILOG series (World Congress and School on Universal Logic), whose first edition took place in Montreux, Switzerland, in 2005, and whose eighth and most recent edition was held in Cusco, Peru, in December 2025.

I also created the World Logic Day, on January 14, 2019, recognized in the same year by UNESCO, as well as the World Logic Prize, a competition among winners of logic prizes from different countries. This adventure began when I decided to create in 2014 the Brazilian Logic Prize, in honor of Newton da Costa, who was my supervisor: alongside my doctorate in mathematics, I also did a doctorate in philosophy in Brazil, under Newton da Costa’s supervision, at USP (the University of São Paulo), on logical truth, concluded in 1996.

2. Flawé: How did you return to philosophy?

JYB:  In fact, I never stopped being interested in philosophy. I always continued to develop philosophical work. Like Plato, I believe that mathematics is, rightly, a first step; but philosophy goes further and higher—and here I am not speaking of the mere history of philosophy, the study of authors taken as an end in itself, or a sophistical kind of argumentation intended only to sustain or “defend” this or that position.

After a two-year postdoctoral stay at Stanford University (during which I worked with Patrick Suppes, in particular on WordNet, a tool I am using for the current project), my first long-term position was  a professorship funded by the Swiss National Science Foundation, for six years, at the University of Neuchâtel (Jean Piaget’s city; his father was the first rector of that university), in Switzerland, from 2002 to 2008. There there was a Department of Logic in the Faculty of Humanities, and I also worked in the Department of Psychology. During that period, I began to take an interest in the question of imagination and in the use of images in philosophy (I began writing a series of articles systematically using images). There is something paradoxical in the fact that Plato rejects images, in the allegory of the cave, by means of an image. I am also interested in the question of symbol and symbolism, a theme that runs through philosophy, mathematics, and psychology (cf. the famous Swiss psychologist Carl Jung; Piaget also spoke about this). During those years, I organized two interdisciplinary congresses at my university in Neuchâtel: one on symbolic thought and another on imagination (later on the 37th edition of the ASPLF congress in Rio on imagination with my colleague from Neuchâtel, Daniel Schulthess), inviting colleagues from various departments. In a certain way, that already anticipated the event we are organizing now.

I returned to Brazil and spent two years, in 2008 and 2009, in the Department of Philosophy at UFC (Federal University of Ceara), in Fortaleza. Then I joined the Department of Philosophy at UFRJ (Federal University of Rio de Janeiro) in 2010, where I remain to this day. There is not much interest in logic there, but every year I teach the compulsory undergraduate course “Introduction to Logic”. In graduate studies, I vary the themes: I have already taught courses on love, on laughter, and on thought. In 2025 I offered courses, in both semesters, on the question “What is it?”, continuing also this year, 2026.

In August 2024, I took part in the 25th World Congress of Philosophy in Rome, where I delivered a general lecture on the question “What is it?” (At the 23rd edition, in Athens, I had organized a roundtable on imagination.) Over the years, I have written more than ten papers with the title “What is X?”, but with Xs connected to logical notions and systems. An important turning point came in 2020 with the article “What is an axiom?”, dedicated to my friend Francisco Doria. That was when I began to develop a more general reflection on how to answer the question “What is it?” starting from this particular case.

After writing a short article on this question for my lecture in Rome, I began, together with my students, over the course of 2025, to develop a general methodology applicable to any X. In the end, I arrived at eleven procedures. With their support, and especially with your own help, I wrote the paper “What is money?”, in which almost all of these procedures are employed. I chose to deal with money because my friend Jamsin Özel invited me to organize a congress with her in Las Vegas in 2024, and I then proposed an event connected to the city with the theme “Logic, Money, and Chance.” My interest in the topic of money is related to my paper “What is an axiom?”, in which I discuss Max Gunther’s famous book The Zurich Axioms, where he presents the methodology used by Swiss bankers, associated with the development of one of the most powerful banks in the world, UBS (Union Bank of Switzerland).

3. Flawé:  How can one answer the question “What is X?” Is there a general methodology applicable to any X?

JYB:  Plato presents a dichotomy between two kinds of answer. On the one hand, there is the answer by enumeration, which I call the “north pole”; on the other, there is the answer by comprehension, which I call the “south pole.” The example of mud in the Theaetetus helps us think about this, as does the case of prime numbers (2, 3, 5, 7 ... vs. divisible only by 1 and itself). I favor a balanced position, which I call the “southern tropical position” (closer to the southern position than to the northern one) and the points I developed, discussing them with my students last year, are directed precisely toward this intermediate position. 

I believe that philosophy is not a matter of personal opinion, nor a collection of “authors,” nor a system of dogmatically crystallized theories. Philosophy is the first step toward the development of science, of scientific theories; but the theory of relativity, group theory, or the theory of evolution, for example, no longer belong to philosophy properly speaking. Socrates is famous for having declared: “I only know that I know nothing.” Yet, by making the question “What is it?” (ti esti) the starting point of philosophy, he transformed the nothingness of not-knowing into the fertile beginning of philosophical inquiry, who led humanity to the moon.

Wittgenstein gave, in Cambridge, a very short lecture defending the view that all traditional philosophy lacked meaning because it exploited abuses permitted by language—which allows one to construct syntactically correct but semantically empty sentences. This ambiguous relation between syntax and semantics can generate interesting poetry; but Carnap, developing Wittgenstein’s idea, argued that philosophy would be a “bad art,” and that philosophers would be failed poets. For him, on one side there would be science and, on the other, art, with no proper space for philosophy. I like the challenging essay of Carnap The Elimination of Metaphysics Through Logical Analysis of Language, but I do not agree with all what he says. 

The work I am developing around the question “What is it?” (ti esti) seeks to return to philosophy’s original point of departure, which is the right one: an investigation that advances understanding, even when it ends in aporia. This is the ninth series of events I am launching; the others were more closely tied to logic in one way or another. This event is as well, because to answer the question “What is X?”, whatever X may be, we need to reason. But it is an event that encompasses all branches of philosophy and is also interdisciplinary. For our event I invited a famous mathematician from the University of São Paulo, who will try to answer the question “What is a number?”. 

I intend to organize this event every two or three years, always in Rio de Janeiro, and it should become one of the major philosophical events in Brazil and in the world. For this first edition, we will have “What is X?” lectures by researchers from all over the world on every kind of X. And Rio de Janeiro is the right place because it close to the Tropic of Capricorn! Plato said that the beginning of philosophy is wonder (thaumazein), and this is directly linked to ti esti. If nothing surprises us, our intelligence does not develop. On the other hand, limiting intelligence to the construction of scientific theories leads to the transformation of reality—the construction of houses, airplanes, computers—but we cannot stop there.

4. Flawé: How does the use of AI work in this project and in the congress connected with ti esti?

JYB:  I have known AI for a long time because, when studying mathematical logic, I also studied computing and programming. I learned the LISP language, developed by John McCarthy, the father of artificial intelligence. My doctoral supervisor in mathematical logic, Daniel Andler, also introduced us to McCarthy’s nonmonotonic logics. Later, Andler left mathematics, created the Department of Cognitive Sciences at the ENS (Ecole Normale Supérieure), and became a professor of philosophy at the Sorbonne, developing in particular a reflection on AI—cf.  his latest book, which you like to use as a pillow for sleeping.

Recently, I was in contact with McCarthy’s widow, Carolyn Talcott, a researcher at SRI (Stanford Research Institute) in California. She took part in our congress Logic, Chance and Money in Las Vegas in 2024, and also in UNILOG 8 in Cusco, in December 2025, where she delivered the lecture “Intelligence and Logic.” 

And my host at Standord University in 2001 and 2002, Patrick Suppes, was a pioneer in the use of computers in education.  I remember him saying that learning with computers should take place at home, so that classroom time can be devoted to interesting non-mechanical discussions.  Suppes was fond of David Hume.  If your aim is to understand Hume’s idea of induction in order to develop a reflection on induction, rather than to become the world’s foremost specialist on Hume, it is better to use AI softwares that can provide an answer in a few seconds than to spend hours reading Hume directly. This can serve as a first step regarding your understanding of  induction according to Hume.and, depending on your objectives, perhaps even as the last.

When I was a child, between the ages of seven and twelve, I read many American science-fiction books. Asimov practically prophesied Wikipedia, which I consider a very interesting project. I also saw Kubrick’s movie 2001: A Space Odyssey, based on a short story by Arthur C. Clarke. As a chess player since childhood, I was also interested in the question of Deep Blue. And I find the hardware/software—body/mind analogy very suggestive.

Recently, things began to change radically with ChatGPT and other programs of the same kind: generative AI. It was you yourself who drew my attention to these impressive capacities, to which I had not been paying so much attention.

For this congress, we are using AI in all its aspects (more info here). But for it to work well, it has to be used intelligently: whoever uses AI in a foolish way will not get very far and may even go astray. The idea is to have a permanent interaction: to make AI more intelligent and, at the same time, to let it make us more intelligent.

To answer the question “What is X?”, by offering a methodology like that of the eleven procedures, AI can take us much further. But it is important to emphasize that the natural intelligence of the human being remains fundamental, especially when it comes to creativity. I do not believe that AI could have arrived, by itself, either at the original formulation of Socrates’ and Plato’s question or at the eleven procedures that we developed to answer it. And there is an important triviality here: generative AI was created by human beings, artificial intelleigence is human; there is no circular mystery like the famous vicious circle chicken or egg. AI is capable of producing a good chicken omelette, but we have to provide it with the material to get there! 

If you ask an AI system to write a ten-page paper on a question such as “What is Induction?” without any further specification, the result will probably be weak. The outcome improves if you give the system relevant material to read and a methodology to follow. But the best result is achieved when you use the AI system by asking it many intelligent questions,  when writing yourself the paper. That’s the recipe that will whip your ideas into a delicious chantilly cream.

5. Flawé: What is the role of the cat Miaou in this story?

JYB:  The cat has played a fundamental role in the history of humanity; one only has to think of Egypt, one of the great civilizations in human history. I named my cat Miaou because “miaou” is the name for cat in the original language of Egypt.

Even today the cat accompanies the human being, and it is very difficult to explain exactly what it is and how its intelligence works—in contrast to the dog, whose intelligence is more similar to that of the human being.

Answering the question “What is a cat?” is a real challenge. That is why I put a picture of my cat on the event poster. Desmond Morris, famous in particular for The Naked Ape, in which he gives a very innovative answer to “What is a human being?”, was also very interested in cats and wrote several books about them.

Miaou appears reading the book Mysteries of the Alphabet by Marc-Alain Ouaknin, the son of a famous rabbi in France and himself a rabbi. In that book, he explains the origin of the alphabet in relation to Moses’ rejection of images. The alphabet was a fundamental instrument in the development of humanity, although few people know the original meaning of those letters, derived from ideograms: aleph, an ox’s head, representing masculine strength; beth, representing the house and femininity; and so on.

All this was gone with the wind, and the alphabet, founded on a rejection of images, became one of the most powerful instruments of human development. “Cat” is a succession of signs that have no meaning in themselves; the combination of those signs is not, in itself, what gives meaning to the word. As Ferdinand de Saussure pointed out, the arbitrariness of the sign is a fundamental principle. That is, in a certain way, the “absurdity” of alphabetic languages. But anyone who knows logic knows that the absurd is the key: it was by means of reasoning by absurdity that the irrationality of the square root of 2 and many other important theorems were proven.

Just as Plato, in the allegory of the cave, uses an image to point toward something beyond images, I too use an image—the event poster—to suggest something that goes beyond the image itself. The cave is a fundamental first step; cf. the aphorsim of Democritus:  truth as a naked woman emerging from the bottom of a well.