The concept of sovereignty and laicism is still being instrumented into different projections to that which have been conceived and used through the french revolution and the old regime. This article is not to discuss that, but to delight how another concept deduced from it becomes antagonistic with it in the French context. Laicity referred to the French V constitution, or the act of 1905, it’s not what it appears, and is mostly known in the French literature, this article is to reject all that, and goes toward an etymological construction of the concept into the french politics since XV century. Then to examination who and how the old regime and the XIX century have been involved with the religious beliefs than to answer the questions: does the revolution been laic or atheist? The answer is useful to go forward with the examination of the french act of the separation of the State from the churches of 1905 and to determine if that act has been laic or atheist. The questions of how the idea of laicism has been reversed into the interwar period thus to the 1958 constitution to be developed in further work, but the conclusion proposed here is the evidence of constitutional inter-contradiction and reversed usage of the concept which is being instrumented today further then constitutional idolatry, but a constitutional nihilism.