Shortly before his death, Eugenio Trías encouraged his editors to reprint The Thread of Truth. Of all his books he was the one that made him see the reader again. As he himself had said, "If there is a book of mine capable of defending alone, this is it. If I were to choose a single book capable of being saved from an imminent catastrophe, I would certainly choose this one. " The thread of truth is an expression of Calderón de la Barca. It refers to the thread that Ariadne gives to Theseus to traverse the labyrinth of Daedalus and fight against the Minotaur. This scenario allows Eugenio Trías to rethink the adventure of knowledge and distill a concept of Truth according to its philosophy of the limit. The construction of its main concepts, such as space, time and the system of categories, is tested in this book in dialogue with works of art (Great Glass by Marcel Duchamp, Citizen Kane by Orson Welles, Fourth Symphony of Brahms) and Classical philosophies (Thus spoke Zarathustra of Nietzsche, The Republic of Plato). It is a text that combines the poetic flight of the literary essay with the conceptual rigor of the philosophical treatise. Undoubtedly, the best way to get into the philosophical world of Eugenio Trías.