Gender difference is a fundamental philosophical and medical question in the Early Modern period, a question often avoided by the history of philosophy. There are essentially two opposing schools of thought on this matter: those who follow in the lineage of Descartes, and those who align themselves with Cureau de la Chambre. Their study of the human condition primarily explores the interactions between body and mind, but more importantly, they highlight the body's unique thoughts through the lens of the imagination. It is the body that decides whether women and men are equal. Critical readings of these two approaches, proposed on the one hand by Malebranche and on the other by Poulain de la Barre, confirm that the 17th century was a turning point in the study of psycho-physiology and morality. The confrontation between these four philosophers allows us to understand the origins of the theoretical perspectives on sex and gender that still hold sway today: that of egalitarianism on the one hand, and that of a gender differentialism that can be either inegalitarian or egalitarian.