This article records tradition as it has been passed down and reported. Its sources are not yet part of the atlas's verified catalogue.
Much of the argument of Phenomenology of Perception turns on a single, deceptively simple observation, that the body does not occupy space the way an object occupies space. A table has a location that can be plotted on a grid, fixed and indifferent to any task; the lived body, by contrast, orients itself around what Merleau-Ponty calls situational spatiality, space organized in terms of actual or possible tasks rather than geometric coordinates. When one reaches for a cup without looking at the hand, or ducks beneath a low doorway never measured, the body already knows where things are relative to what it is trying to do, in a way that has nothing to do with calculating positions the way one object's position might be calculated relative to another. Merleau-Ponty calls this pre-objective, task-oriented organization of the body the body schema, and he treats it as more fundamental than any explicit representation of the body's geometry.
The clinical evidence he leans on most heavily comes from the case of Schneider, a patient studied by Gelb and Goldstein whose brain injury, sustained in the First World War, left him unable to perform certain everyday actions while leaving others intact. Schneider could still execute habitual, concrete movements, swatting a mosquito on his own arm, for instance, but he lost the capacity for what Merleau-Ponty calls projecting into virtual space, movements that require imagining a situation not actually present, such as pointing to a part of his body on command with no immediate practical occasion for doing so. This dissociation is philosophically significant because it shows that the body's spatial orientation is not one single capacity but something built from what Merleau-Ponty terms the intentional arc, a structure that projects around us our past, our future, our human milieu, our physical situation, binding perception, movement, memory and possibility together into a single field. Schneider's injury did not simply damage his motor skills or his intellect narrowly conceived; it damaged the arc itself, the connective tissue that lets a body live toward possibilities rather than merely react to a present stimulus.
The phantom limb, discussed alongside Schneider's case, works the argument from a different angle. A patient who continues to feel sensation in an amputated leg cannot be explained by a purely physiological account, since the nerve pathways in question no longer exist, nor by a purely psychological account that treats the phantom as an idea or a memory the patient consciously entertains, since the sensation persists whether or not the patient is thinking about the missing limb at all. Merleau-Ponty argues that the phenomenon belongs to neither register cleanly because it expresses the body's continued practical orientation toward a world that still solicits two-legged action, an organism's ongoing being-toward-the-world that outlasts the anatomical fact of the limb's removal. The body, on this reading, is not a machine to which a mind is attached, nor a set of sensations to be inventoried, but a system of possible actions whose habitual grip on the world can persist even after the very organ that grip depended on is gone.
Taken together, Schneider and the phantom limb push Merleau-Ponty toward the same conclusion from opposite directions, one a subtraction of practical possibility despite an intact body, the other a persistence of practical orientation despite a missing body part. Both cases resist explanation by the two vocabularies, mechanistic and intellectualist, that had dominated psychology before him, and both therefore serve as evidence for the body schema as a third, irreducible kind of structure, neither pure matter nor pure thought, through which a body inhabits a world of tasks rather than merely occupying a location within it.