Like many existentialists Marcel eschews systematic thought or interlocking philosophic abstractions. He presents his "various data" in a manner that is always reflective, exploratory, occasionally contradictory—proceeding from flashes of insight or acute psychological dissections of particular, concrete situations, rather than from consistently elaborated premises. His style is properly matched to his favorite journal form—periodic entries which return to, as well as abandon, a few dominant themes. Nonetheless, in two major works, The Mystery of Being and Being and Having …, something like a system of concerns can be identified.

For Marcel, intersubjectivity, that is, the intimate, subjective relation between two persons (I and Thou in Martin Buber's terms), is the "cornerstone of a concrete ontology." Hence, in this "metaphysic of we are as opposed to a metaphysic of I think," Marcel asserts that "love as the breaking of the tension between the self and the other, appears...