Emile or On Education poses a problem for interpretation concerning the relationship established right from preface of the book between enunciation of a sound positive knowledge of the subject to educate and the evocation of a “system” which takes the form of “starry-eyed dreams of a visionary about education”. This dicotomy, more accentuated still by the break Rousseau marks between “the pure goodness of the scheme” and its implementation in conditions that are always quite particular, has complicated the task of those who wanted to engage themselves in following it through. This was the case of the artisans of the New Education at the very heart of the “crucible of the sciences of education” that Geneva was in the first half of the xxth C entury: for these artisans, the establishment of a “science of the child” did not cease to interfere with a “humanist” aim which most often took the form of militancy, and which has remained the blind spot of educational thinking. And the transition to the “sciences of education” has not made the problem disappear. This article seeks to philosophical clarification of the “humanist” dimension in its relationship with the “scientific”, and to link the two in a epistemology of teaching which could still be useful today.