In addition to being a fist class scientist André-Marie Ampère was also a first class philosopher, and especially an epistemologist of exceptional talent. Although he became famous for his groundbreaking work in electromagnetism, he has today remained virtually unknown as a philosopher. I will focus, here, on his less known work in epistemology ; that is, on the revolutionary method of investigating his classification of human knowledge, a method which he called “cautious probing” (tâtonnement) aimed at harmonizing interacting relationships between opposites, something similar to the coincidence of opposites in Nicholas of Cusa or the change of voice register in Bel Canto singing.