Plutarch is often seen as a dualist philosopher. Yet, when one studies the texts which are most often quoted to back such an opinion, the so-called dualist doxographies in De Iside et Osiride and in De animae procreatione, one is actually lead to think otherwise. When they are replaced in their context, it so happens that these texts describe the conditions to obtain harmony and the mixing of the contraries which are both necessary to the birth and to the very existence of the universe. However, harmony and mixing cannot be obtained without the receptacle of the contraries that constitute them. Far from being a simple intermediary , this receptacle, which takes different aspects in the different treatises, is indeed a constituent principle according to Plutarch. Without it, there can be neither encounter nor opposition of the contraries, and so, paradoxically, precisely because it is a guarantee of dualism, it makes dualism disappear. Dualism then turns out to be a mere preparatory step in the elaboration of a really triadic philosophy. Plutarque est sans doute le philosophe platonicien qui ouvre le plus explici-tement la réflexion sur le dualisme. Même s'il emprunte, directement ou non, à Aristote 1 , à une tradition scolaire à la fois platonicienne et néopythagoricienne 2