Duhem's hour came the following morning when he attended, in the philosophy section of the Congress, some lectures dealing with topics that touched on the relation of sciences to metaphysics. After the Pere Bulliot, future head of the philosophy department of the Institut Catholique in Paris, had read his paper on the concepts of matter and mass, Duhem asked, not without the promptings of some present, for permission to make a few remarks. Although his remarks were not reported in the Compte rendu of the Congress in the form of a verbatim quotation, the printed text can, partly because of its incisiveness and clarity, be taken for the most part for Duhem's actual words. Duhem, the report begins, 'is convinced that these researches [having for their object the confines of the positive sciences and metaphysics] will, if done wisely and prudently, lead to the reconciliation of Christian philosophy and modern science, but he insists on the extreme difficulty of such studies.' Duhem's reasons were as follows:
Only the principles of the different positive sciences are of interest to philosophers; but, in order to know these principles, it is not enough to read a book of popularization, not even the first chapters of a treatise written by a competent scientist. One does not comprehend the meaning and bearing of the principles on which a science rests except when one has studied that science for years, applied in a thousand ways those principles to particular cases, and mastered in depth the technique of what the Germans call the materials of science.
For example, the obvious sense of Euclid's [parallel] postulate is accessible to a child who studies the first book of geometry. But in order to understand the exact sense of that postulate, to grasp the reasons which give it a special place among the truths of geometry, to see clearly what would become of geometry if that postulate were to be abandoned, one must have a complete mathematical training which requires years of work.
If therefore we want to handle with competence and fruitfully the questions which are of the domain common to metaphysics and to positive science, let us begin with studying the latter for ten, for fifteen years; let us study it, first of all, in itself and for itself, without seeking to put it in harmony with such and such philosophical assertion; then, as we have mastered its principles, applied it in a thousand ways, we can search for its metaphysical meaning which will not fail to accord with true philosophy.
Anyone who would find exaggerated a similar labor must not forget that every hasty, scientifically incorrect solution of one of the problems relating to the common frontiers of science and philosophy, would result in the greatest prejudlce against our cause. The philosophers must imitate the patience of scientists. Once a problem is posed, scientists devote centuries, if necessary, to solving it. They accept only a precise and rigorous solution.
At any rate, the schools we are combatting give us example. The positivist school, the critical school, publish numerous works on the philosophy of science. These works carry the names of the greatest names of European science. We cannot triumph over these schools except by opposing them with researches done by people who, too, are masters of the positive sciences.
[quoted from Compte rendu du Troisième Congrès Scientifique International des Catholiques tenu à Bruxelles du 3 au 8 septembre 1894 (Bruxelles: Société Belge de Librairie, 1895) in Jaki, Uneasy Genius: The Life and Work of Pierre Duhem, 113-4, emphasis added]