A theory of legal constraints start with a realistic conception of the interpretation, according to which the legal actors (ie. authorities authorized to produce legal rules) are free to choose between several possible meanings of the texts which they have to apply. Nevertheless, the legal actors do not decide in a completely arbitrary way. From the observation of their decisions, appear coherences. Numerous factors can explain it: sociological, political, psychological, conventional factors… The theory of the legal constraints suggests bringing to light, among all these factors, the existence of some which are specifically legal, that is emerging from the configuration of the legal systems such as the legal actors represent it themselves. This representation is connected to the conception that the actors have of their own power and of the power that other actors have on them, in their conception of the modalities of the legal argumentation and the functioning of the legal system.