The purpose of this work was to understand the reform of the disciplinary regime of the conscript soldier within the special regulations of the Military Forces. Using a documentary compendium submitted to a comparative and contextual analysis within disciplinary law, it could be established as a cornerstone for the genesis of the reform and the application of the new disciplinary regime to conscripted soldiers, the concept of substantial illegality. This concept is based in two fundamental concepts: the relationship of subjection and material unlawfulness. Understanding these concepts it could be concluded that the soldier conscripted through the formality of his relationship and the functions within the framework of the military forces, emerges from his civil nature and consequently becomes a disciplinable subject under the law 1862 of 2017.