Constitutionalism is the idea equated with the concept of the "Rule of Law", that government can and should be legally limited in its powers, and that its authority depends on enforcing these limitations.
Constitutionalism does not recognize the sovereignty of the legislature. Instead, it only recognizes the sovereignty of people. The legislature is a creature of the constitution and is governed by the constitution.
Constitutionalism can be said a political system with following features:
1. All including the entire system of government is governed by the supreme law, generally called constitution.
2. Only the people's will can supersede and change the supreme law
3. Changes cannot be made frequently due to the difficulty of getting the requisite popular support
4. Separation of power among the various organs of govt., and an independent judiciary.
Separation of power has to be combined with checks and balances. By giving each branch of the government some control over the other branches to prevent one branch of the government from becoming too powerful and therefore dangerous.
For example, if there is no executive veto power to executive, then the legislature will eventually get all powers of the government. Also in Indian constitution, the parliament has no unilateral power to amend the Constitution; doctrine of judicial review is present to put checks and balances.
Liberal constitutionalism is based on a particular view towards human nature, which is universal self-interest. Because rulers, like ordinary people, are self-interested, rulers also need to be disciplined and constrained by the rule of law.
Constitutionalism can be further strengthen by excellent administrative structure, regular conduct of elections, passage of revolutionary acts act RTI, NREGA and empowering the people by encouraging participation in govt. business.
As mere presence of political parties and election don’t make a country democratic, similarly a country may have constitution but not necessarily constitutionalism.
Some Appreciation Please!