Since Descartes, Western philosophy had split the human in two: on one side the thinking mind (res cogitans), on the other the body extended in space (res extensa). The true subject of knowledge was the mind; the body a machine it carried. The French phenomenologist Maurice Merleau-Ponty (1908–1961) rejected this division at its root.

His "Phénoménologie de la perception" (Phenomenology of Perception), published in 1945, carries Husserl's phenomenology and Heidegger's idea of "being-in-the-world" into the body. For Merleau-Ponty we do not first think the world, we first perceive it; and perception is not the work of an abstract mind but the act of a body that touches, walks, and reaches into the world. When I "grasp" a door handle I do not first represent it mentally and then take hold; my hand knows directly. The body is not an object I think about but the medium with which I think — the "lived body" (le corps propre).

This means the subject is not a spectator cut off from the world. I am not an eye looking at the world but an embodied being settled within it and directed toward it; the horizon of my perception is always shaped by my body's position, my past, my habits. Merleau-Ponty rethinks space, depth, and even time from this embodied gaze. The illusion of objectivity — the claim to see the world from nowhere, with a neutral eye — thereby collapses; every seeing is a point of view.

This concept of "embodiment" is the third great pillar of phenomenology after Husserl and Heidegger, and its influence reached beyond philosophy: theories of the "embodied mind" in cognitive science, the role of the body in knowledge in artificial intelligence, debates on spatial experience in art and architecture all return to this source. When Merleau-Ponty died suddenly at 53, his thought on perception, language, and visibility was still unfinished; even this incomplete project became one of the most fertile philosophies of the century.