How to describe a person in his non-interchangeable dimension? Which scientific discipline does this work? In order to answer these questions, this introduction, which prefers the notion of singularity to that of subjectivity, considers several points, by being critical of the social sciences in general. If an individual is presented as “turned towards” others and the world, and if the theoretical and methodological place given to others and contexts is significantly important, is there not a risk of moving the focus, thus “losing” this individual in his entirety and details of his singularity? Thus presented, he is a bit like coming out of himself. There is also the question of the importance to be given to the continuity of moments in such a description, whereas life stories or classical ethnography almost naturally favour a discontinuity of situations. Aware of the difficulty of such observations and descriptions, the conceptual and methodological answers are attempts, like asymptotes that it is important to always try and complete. At the same time, this introduction also questions some of the limits of existentialist thinking.