What is the concept that government must be conducted according to constitutional principles?

Every organisation/institution/society works on a principles of laws and rules to which all layers of these entities abide and which make things "work". For instance in a government its the constitution in which the basic laws and fundamental rights which pertain to all individuals within its society are set. From it stems order within society and a level of control by the government on society. Democratic accountability is a means to insure all levels of the government are playing by these rules which apply to them as well. This would be the control of society on the government.

So i am left with 2 principles: order and accountability. Order as a direct result of the constitution (Laws), and accountability as effect of the constitution (Rights).