advocacy of a system of government according to constitutional principles
implies a balance between authority and power of the government on the one hand, and on the other hand the rights and liberties of the subject or citizen; also the limitation of government by law and the rule of law; a constitution may be unwritten (British and Canadian) or written (American). (p. 548)
Constitutionalism is the limitation of government by law. Constitutionalism implies also a balance between the power of the government on the one hand and the rights of individuals on the other.