The Critique of Dialectical Reason has a subtitle: Theory of Practical Ensembles. We should use this subtitle as the starting point of our study. What is a practical ensemble? It is a configuration of human intersubjectivity affecting materiality and vice versa. Does anything else exist in our world? In the first volume of the Critique, Sartre describes four different types of configuration: the series, the group, the organization, and the institution. In the following pages I will discuss these modes of practical human relations as they are integrated into our concrete social world. I will start with Being and Nothingness, in which the conception of intersubjectivity is quite different from the one later favored by Sartre in the Critique. This original conception is nevertheless retained partially in the latter, and therefore needs to be examined.