A constitution which effectively restricts the legislative powers of the supreme legislature in the system does not do so by imposing (or at any rate need not impose) duties on the legislature not to attempt to legislate in certain ways; instead it provides that any such purported legislation shall be void. It imposes not legal duties but legal disabilities. ‘Limits’ here implies not the presence of duty but the absence of legal power.

H. L. A Hart, The Concept of Law, loc. 261