Charles-Edouard Niveleau's work aims to rediscover the historical (although forgotten) roots of the phenomenological movement that appeared through a confrontation with natural sciences and the emerging scientific psychology during the nineteenth century in Germany. Charles-Edouard Niveleau hypothesis is that phenomenology is linked to the development of natural sciences, especially physiology, and that phenomenology is intrinsically experimental precisely because it cannot be separated to the science in the making.
The first part focused on the historical background and development of experimental phenomenology from Goethe to Ewald Hering who represented the key-figure in the phenomenological movement which dominated the history of psychology from the 1890s to the late 1930s. Following Stumpf Hering seems to be one of the first scientists (after Goethe and Purkinje) who introduced the phenomenological methodology in psychology. Hering considered the description of sensible qualities as a legitimate field of investigations and recognized the priority status of phenomenology on all other sciences. The physiological explanation should be considered as posterior to the description of perceived phenomena which would determine it by giving its explanandum. Carl Stumpf largely emphasized and developed systematically such a conception of phenomenology. The descriptivist approach originating in the controversy on the very nature of color between Goethe and Newton, his further defense and development by Purkinje, the continuation of this bipolarity between two paradigmatic approaches in vision sciences with the controversies between Hering’s school and Helmholtz’s one were Charles-Edouard Niveleau's main concerns in order to introduce phenomenology as an irreducible level of reality.
The second part was devoted to phenomenology as an effective methodology in natural sciences in general and in psychology in particular. Which conception of phenomenology did Stumpf defend? In what sense can we qualify it as "experimental"? Contrary to a widespread opinion, Stumpf cannot be considered as a strict orthodox brentanian. Even if he serves the same ideal for a scientific philosophy, even if his phenomenology is determined in relation to Brentano’s empirical psychology in his famous 1907 papers, it is not exact. Stumpf never explicitly opposed to Brentano but no doubt that he was quite suspicious about the use of internal perception. This issue is particularly crucial to know whether there is a phenomenological methodology properly speaking or if the use of quantitative and statistical methods is adequate. To which extent can Stumpf consider the quantitative methods as relevant for phenomenology itself without making any confusion between phenomenology and experimental psychology? What is the very nature of the polemics between him and Wundt (and Lorenz) if they both agree with the use of quantitative methods in experiments? Do we need to subscribe to and follow some fundamental rules of description in order to make some phenomenology?
In the third and last part of the project Charles-Edouard Niveleau offered an exercise of experimental phenomenology. Thus, special attention was devoted to the concept of tonal fusion and its relationships with consonance perception that constitutes one of the main areas of Stumpf’s research. Charles-Edouard Niveleau used this issue of Gestalt formation and perception to confront the physicalist approach paradigmatically advocated by Helmholtz and Wundt’s school with Stumpf’s phenomenological approach. To which extent does the Gestalt issue thematically define the phenomenological movement in psychology? Why are there so different conceptions of Gestalt if his main investigators apparently agree with the use of a descriptive approach? Charles-Edouard Niveleau investigated in particular the controversies between Stumpf, Theodor Lipps, Hans Cornélius, Alexius Meinong, and Stefano Witasek, Félix Krueger and Charles-Edouard tried to determine the experimental ground which can motivate the acceptance or rejection of the constancy hypothesis. Finally Charles-Edouard showed what has been gained by Stumpf and lost by Köhler in their understanding to the concept of Gestalt.