The object is to draw a comparison between Blanchard's approach and the one put forward in present-day urban research. It is remarkable that many research themes investigated today were present in Blanchard's monograph... without the analytical jargon. It appears, however, that Blanchard had difficulty to take sufficiently into account social structures as constraints and individuals as actors in his interpretations. Why was this the case since, in theory, his mode of thinking, a possibilism not unrelated to the cybernetic form of explanation, would have allowed it?