Duty Quotes in City of Bones Page 1

And Jace and the other Shadowhunters must adhere to it. No questions asked.

Here, Jace is telling Clary that she can tell Simon all about the Clave, etc., because she isn't forbidden to do so. We have a feeling that Jace wouldn't tell Simon anything even if he had a gun pointed at his head. There are some rules you just don't break.

Sure, that pledge sounds a lot like a law, designed to get the Shadowhunters to do their duty. But things get grayer when you consider the fact that who falls into the category of "people" is debatable.