After 9/11, the notion of emergency attracted much interests from constitutional scholars. The crucial question is whether a properly "legal" framing of emergency situations is conceptually possible? In this paper a phenomenology of emergency first considers what the invocation of an emergency may result in from the point of view of the powers which are conferred to legal actors. The study of the ontology of emergency secondly tries to elucidate the concept of emergency as it appears in legal actors' reasoning. Rejecting ontological realism, an analytical approach successively envisions the denotation and the connotation of "constitutional emergency". An argumentative analysis of constitutional emergency, displaying both the strengths and weaknesses of the strategic rhetoric it belongs to, is proposed.