In the following article, I will talk about the political and juridical thought of Emmanuel Sieyès, theorist and actor of the French Revolution. My goal is to demonstrate that the specificity of this thought is to be situated on both sides of the revolutionary crisis: it emerged in the public space in 1788, and its last developments were linked to Bonaparte’s coup of the year VIII1. More specifically, my purpose is to think about the way its evolution reflects, by its changes of tone and its conceptual displacements, an event such as the transition between the Ancient Regime and French society after 1789. The originality of Sieyès’s thought lies in the way it is divided between a critic or rebellious moment – perceptible in the early pamphlets of 1788 and 1789 – and a conservative moment which finds its full expression after Thermidor and the fall of Robespierre.