Maurice Merleau-Ponty (1908-1961) is a French phenomenologist philosopher, strongly influenced by Edmund Husserl, and often somewhat mistakenly classified as an existentialist thinker because of his acquaintance with Jean-Paul Sartre and his distinctly heideggerian conception of Being.
In his Phenomenology of Perception (first published in French in 1945), Merleau-Ponty developed the concept of the "body-subject" as an alternative to the cartesian "cogito". Consciousness, the world, and the human body as a perceiving thing are intricately intertwined and mutually `engaged'. The phenomenal thing is not the unchanging object of the natural sciences, but a correlate of our body and its sensory functions. Taking up and coinciding with the sensible qualities it encounters, the body as incarnated subjectivity intentionally reconstructs things within an ever-present world frame, through use of its pre-conscious, pre-predicative understanding of the world's make-up. Things are that upon which our body has a grip, while the grip itself is a function of our connaturality with the world's things.
The essential partiality of our view of things, their being given only in a certain perspective and at a certain moment in time does not diminish their reality, but on the contrary establishes it, as there is no other way for things to be co-present with us and with other things than through such "Abschattung". The thing seen in perspective transcends our view, and yet is immanent in it. By a pre-conscious act of `original faith' we immediately place this phenomenal thing in the world, where it blends in with other things and behaves like any "figure" against a certain background. Just as much as our own unity as a bodily subject is not a unity in thought, but one that is experienced in our interaction with our surroundings, so the unity of the thing is `perceived' as pervading all of its perspectives. We do not consciously construct the thing, but rather allow it to construct itself before our eyes; only when this unconscious process results in perceptive ambiguity, i.e. when the body is unable to present us the thing in any clearly articulated way, the subject will consciously interfere and clarify his perception. Apart from such instances, the subjectivity of the perceiving body operates unknown to the conscious subject, engaging the pre-objective factuality in which it too participates, and disclosing the rationality of the world to the subject. Thus we encounter meaningful things in a unified though ever open-ended world.
Critics have remarked that while Merleau-Ponty makes a great effort to break away from Cartesian dualism, in the end the "Phenomenology of Perception" still starts out from the opposition of consciousness and its objects. Merleau-Ponty himself also acknowledged this, and in his later work proceeded from a standpoint of unity, replacing notions that still centre around the subject by notions of "Being" and the essential reversibility of seeing and being visible.