During his lifetime, Henri Poincaré published three major philosophical
books which achieved great success: "La science et l'hypothèse" (1902),
"La valeur de la science" (1905) and "Science et méthode" (1908). After
his death in 1913, a fourth volume of his philosophical works was
published by his heirs as "Dernières pensées" (1913). The four books
constitute the core of Poincaré's philosophic works and were given an
ovation by scientific and general public. Around 1919, Gustave Le Bon
wrote to Poincaré's widow. As the director of the "Bibliothèque de
Philosophie Scientifique at Flammarion", he asked her permission to
publish a second posthumous volume. "L'Opportunisme scientifique" was
intended to be the fifth and final volume of Poincaré's philosophical
writings. Louis Rougier had elaborated the project, with the
collaboration of Gustave Le Bon, and the approval of the philosopher
Émile Boutroux and his son Pierre. Because of the reservations of the
mathematician's heirs, this book was never published and Dernières
pensées remained his last philosophical book. Nevertheless Poincaré's
correspondence - which is kept in the Poincaré Archives at University
Nancy 2 - contains a large amount of documents concerning the project,
its justification and the discussions between Louis Rougier and the
mathematician's heirs. The aim of this book is to restore this episode,
which gives some crucial informations about editorial practices of
Poincaré and about the posterity of his philosophic thinking.