Following Montesquieu's theory of the "separation of powers", only Parliament has the power to legislate; but in the event that a statute is ambiguous, the courts have exclusive power to decide its true meaning, using the principles of statutory interpretation. Since the courts have no authority to legislate, the "legal fiction" is that they "declare" (rather than "create") the common law. The House of Lords took this "declaratory power" a stage further in "DPP v Shaw", As Parliament became ever more established and influential, Parliamentary legislation gradually overtook judicial law-making such that today's judges are able to innovate only in certain very narrowly defined areas.