My explanations start with Kant's transcendental justification of Euclidean geometry. In the second step I will present a brief description of the “revolutionary” developments in geometry within the 19th and early 20th century, which led to a reform of the axiomatic. This, of course, refers to the establishment of non- Euclidean geometries, in which the Euclidean parallel-postulate is replaced by one of its contradictories, so that the traditional geometry doesn’t loses its consistency. The explanation of the new kinds of geometries and their philosophical consequences leads me to the third section, in which I will deal with the phenomenological justification project exposed in Oskar Becker’s “Beiträge...”. In the beginning I will reflect critically upon Becker's critique of the theory of science. The focus here is on the very idea of a “phenomenological” justification of geometry in contrast to a pure scientific (mathematical and physical) reasoning. Then I will discuss Becker's phenomenological proof for the aprioristic character of the Euclidean geometry as well as his idea that the Euclidian space still holds an exceptional status.