The skeptical version of the realist theory holds that judicial interpretation, performed by an authentic interpreter, is an act of the will, that interpretation cannot be true or false and is necessarily valid, whatever its content, that it is the interpreter who is the real producer of the norm and not the author of the text subject to interpretation. Such a theory faces some serious objections. According to one of the most difficult, if this were true, judges would not be bound to follow any rule; they would be free to decide according to their preferences or even their whims; their decisions would be without coherence or continuity. Yet, we see that law, even judge made law, possesses the characteristics of a system and follows certain patterns. Using the classic distinction between having an obligation and being obliged, I will show that, while judges have no obligation to issue certain decisions, they are obliged or constrained by the system. Such an answer presupposes a causal theory of law and I will then argue in favor of such a theory.