In this chapter, I argue that rather than echoing a perception of fundamental rights as principles, and of law as practical reasoning, as the Alexyan theory would want it, the force of proportionality in French public law lies in its aura of value-proof objectivity and scientific correctness. The spread of proportionality thus expresses the mystery surrounding political moral choices in French legal thought. At the same time, it expresses domestic lawyers’ search for a legal science, exempt from subjective moral or ideological evaluations, which could rationalise such choices. Proportionality in French public law has not served so much as a tool for legal change, as the transplant account of its spread would suggest, but rather as a conceptual tool in the hands of the doctrine for systematising and justifying evolutions in domestic judicial review.