The aim of my thesis on colour theories of the Enlightenment and their influence on avant-garde art, was to show the different approaches of modernist artists to the tradition of colour research at the turn of the 18th and 19th centuries. The starting point of the text is the critical analysis of Newton's colour theory, which was conducted by Goethe. The emphasis on empirical experience, which laid the basis of this new science, had a big influence on the work of painter and friend Philipp Otto Runge. The synesthetic theory of George Field also shows an interesting connection to the work of the fin de siècle. The symbolist colour theories are discussed because of their importance to the artists who opened the path to abstract painting, for example Frantisek Kupka, Pieter Mondrian and Vasilij Kandinskij. A chapter was also dedicated to Robert Delaunay, who developed a very sophisticated explanation of how to represent movement in colour contrasts. The American synchronists, who were very proud of their specific artistic movement, were also inspired by Orphism. An important part of the thesis is the focus on Bauhaus artists. Some of them were influenced by the painter Adolf Hölzel, a native of Olmütz in Moravia, who was very interested in Goethe's Farbenlehre. Johannes Itten, a student of Goethe's, was the...

L'oeuvre plastique et l'oeuvre écrit d'Otto Freundlich (1878-1943) sont traversés par une grande thématique : celle d'une volonté de renouvellement de l'esthétique dans une quête de vérité, au coeur de laquelle se situe le rapport perceptif de l'être humain à la nature. Pour Otto Freundlich, qui adopte dans le champ de l'art une position d'artiste plasticien et d'artiste philosophe, ce renouvellement s'opère non seulement par l'intervention de l'artiste mais aussi par la perception visuelle des oeuvres. L'apparente hétérogénéité de son parcours artistique est donc sous-Tendue par une grande cohérence que cette thèse examine à travers une analyse d'une part diachronique des oeuvres plastique et écrit dans leur ensemble, d'autre part en rendant compte dans un même temps et de manière synchronique des modifications qui les affectent et de leurs modalités. Pour ce faire, cette recherche s'appuie sur le travail fondamental lié à la monographie d'artiste : l'étude précise des sources originales écrites principalement en gothique allemand, l'apport de sources inédites, l'analyse des oeuvres et du contexte de leur genèse, au sein du réseau international qu'Otto Freundlich tisse avec les acteurs du champ culturel présents en Allemagne et en France. Cette approche permet non seulement de corriger certaines données historiques mais aussi d'apporter des éléments nouveaux dans l'étude iconographique, iconologique et conceptuelle des oeuvres, isolément comme globalement. / A main thematic pervades Otto Freundlich's works of plastic art and writings : the will to renew the aesthetic in a quest for truth, in the center of which is the perceptive relation of the human being to nature. Otto Freundlich positions himself in the art field as a visual and a philosopher artist. To his mind, this renewal occurs not only through the intervention of the artist, but also by visual perception of works. The apparent heterogeneity of his artistic journey is underpinned by a strong coherence. This thesis examines his works of art andwritings diachronically as a whole, on one hand, and the changes and causes of their emergence synchronically, on the other. This research is founded on the methodology used for artist's monograph: a detailed study of the original sources written mainly in Gothic German, the contribution of unpublished sources, the analysis of works and of the context of their genesis within the international network Otto Freundlich weaves with the art field actors living in Germany and in France. This approach not only enables to correct some historical data, but also provides fresh elements in the iconographical, iconological and conceptualinterpretations of his works, separately and taken as a whole as well.