Thomas Hobbes, an early English philosopher attempted to set out 19 "natural" laws in his work Leviathan. No 3 went something like this;

The third Law is that men perform their covenants made. In this law of nature consisteth the fountain and original of justice... when a covenant is made, then to break it is unjust and the definition of injustice is no other than the not performance of covenant. And whatsoever is not unjust is just.

He probably wasn't thinking about solar electricity rebates when he came up with that one. I think he also had one about an inherent right of self defence in there as well.