What is Constitution?
It is in short, a rule of book of a nation, codifying rule of law.
Constitution is a legal document having a special legal sanctity, which sets out the framework and the principal functions of the organs of the government of a state, and declares the principles governing the operation of those organs. Like every other Constitution, the Indian Constitution also seeks to establish the fundamental organs of government and administration, lays down their structure, composition, powers and principal functions, defines the inter-relationship of one organ with another, and regulates the relationship between the citizen and the state, more particularly the political relationship. The states have reasserted certain principles of law through written Constitutions.
Constitution means the structure of a body, organism or organization, or we can also say what constitutes it or what it consists of. Because the nation is one of the biggest in the world with most of varieties of the people and the cultures, India needs an expressly written code of governance, more specifically when the people chose to have different institutes, estates, mechanisms and levels of sovereignty. And thus we have the longest written constitution, which is one of the essential features of democratic federation.
What is Constitutionalism?
Having a Constitution itself is not Constitutionalism. Even a dictator could create a rulebook calling it
Constitution, which never meant that such a dictator had any faith in Constitutionalism. Recognizing the need for governance, the Constitutionalism equally emphasizes the necessity of restricting those powers.
The Constitutional law means the rule, which regulates the structure of the principal organs of the
Government and their relationship to each other, and determines their principal functions. The rules consist both of legal rules enacted or accepted as binding by all who are concerned in Government. All the Constitutions are the heirs of the past as well as the testators of the future.
Thus the Constitutionalism, in brief, is specific limitations on general governmental powers to prevent exercise of arbitrary decision-making. Unlimited powers concentrated in a few hands at the helm of affairs and their exercise would jeopardize the freedom of the people. These powers have to be checked and balanced with equally powerful alternatives in a system, where it will be nearly impossible for dictators to emerge. In one word ‘Limited Governance’ is the Constitutionalism, which is supposed to reflect in the Constitutional Law of a democratic state.
Constitution of India is the Constitutional Law incorporating the Constitutionalism. The listed fundamental rights and guaranteed remedies, creation of judiciary as an impartial arbiter with all independent powers besides broad based legislative check on the executive are the reflections of such constitutionalism. From these essential characters the doctrines of judicial review, rule of law, separation of powers, universal franchise, transparent executive, fundamental right to equality and quality of life emerged and consolidated.

Preamble:
The concept of “We the people…” being the source and authority for drawing up the Constitution was also taken from the US model and preamble begins with those words.
Preamble is a statement of objects, which are expected by the Constitution makers to be realized through the implementation of the Constitution. In Berubari Union and Exchange of Enclaves, AIR 1960
SC 845, the Supreme Court considered the preamble a key to open the mind of the Constitution makers.
It is a guide to interpretation of the provisions of the Constitution.
Preamble made it clear that Constitution emanated from the people of India and not from any external authority or any less authority than the people of India. Many Constitution experts and the Supreme
Court stated that it is a conclusive assumption and a legal fiction, which cannot be tested or questioned in any court. Supreme Court held that the preamble was part of the constitution and it could be amended except the basic features in the Preamble. 42nd Amendment inserted three "Secularism,
Socialism and Integrity" in Preamble. As these concepts were already implied in the Constitution, the addition was not considered to be the amendment of the basic features.
Salient Features
The basic philosophy of our Constitution is summed up in the Preamble, which declares India to be a
Sovereign Socialist Secular Democratic Republic.
1. Largest Written Constitution
2. Sovereign Socialist, Secular Democratic Republic
3. Parliamentary form of Government
4. Partly Rigid and Partly Flexible
5. Fundamental Rights
6. Directive Principles of State Policy
7. Fundamental Duties
8. Adult Suffrage
9. An Independent Judiciary
10. A Secular Socialist State
11. Single Citizenship

Rule of Law
Aristotle defined rule of law as “Government of law” as opposed to “Government of Man” i.e. a government, which does not work according to the whims and fancies of man but according to law. Rule of law is derived from the French phrase “La Principe de Legalite” i.e. the principle of legality. It refers to a government based on the principles of law and not of men. In this sense the concept of la principi de legalite was opposed to arbitrary powers.
Later, A.V. Dicey gave meaning to the term rule of law. According to him, it implied three things:
Absolute Supremacy of law: as opposed to arbitrariness or wide discretionary powers in the hands of the government.
Equality before law: it enunciates a democratic principle of equal subjection all persons to the ordinary law of the land as administered by the ordinary courts.
The rights of the people must flow from the customs and traditions (rights have common law origin):
Legislative and the rule of law: the acts of legislative would amount to rule of law. If legislature passes laws which lays down overall development of the individual which includes not only civil and political rights but also social, economic, cultural and educational rights of the individual necessary to enhance the development of his personality.
Executive and the rule of law: It would amount to rule of law: When the executive does not exceed the powers given to it i.e. when it is non arbitrary and non discretionary in its actions, If it is able to effectively maintain law and order, When the procedural safeguards are being followed. To ensure “fair play in action” the executive should follow the principles of natural justice:
-Right to be heard
-Right against bias
-Speaking order
Criminal process and rule of law: it would amount to rule of law: When there is certainty of rule of law.
“The rule of law means that decisions should be made by the application of known principles and rules in general, such decisions should be predictable and the citizens should know where he is. A decision without any principle or rule is unpredictable and is the antithesis of a decision in accordance with the rule of law”
-When there is a presumption of innocence
-When there is a rule against double jeopardy

-When there is a rule against self incrimination
-When there is a right to speedy trial and to be represented by a lawyer.
Judiciary and rule of law: it would amount to rule of law when: An independent and impartial judiciary is erected. Independence of judiciary is essential because it would otherwise lead to usurping of power by one organ of the state leading to tyrannical laws.
The Supreme Court, in In re Vinay Chandra Mishra’s case (1996) 2 SCC 584 stated that “the rule of law is the foundation of a democratic society. The judiciary is the guardian of rule of law. In a democracy like ours where there is written constitution which is above all individuals and institutions and where the power of judicial review is vested in the superior court, the judiciary has a special and additional duty to perform i.e. to see that all the individual and institutions including the executive and legislative act within the framework of not only law but also the fundamental law of the land.
Separation of Powers:
The doctrine of Separation of Powers deals with the mutual relations among the three organs of the
Government namely legislature, executive and judiciary. The origin of this principle goes back to the period of Plato and Aristotle. It was Aristotle who for the first time classified the functions of the
Government into three categories viz., deliberative, magisterial and judicial Locks categorized the powers of the Government into three parts namely: continuous executive power, discontinous legislative power and federative power. “Continuous executive power” implies the executive and the judicial power, „discontinous legislative power ‟ implies the rule making power, „federative power ‟ signifies the power regulating the foreign affairs.
The French Jurist Montesquieu in his book L. Esprit Des Lois (Spirit of Laws) published in 1748, for the first time enunciated the principle of separation of powers. That i s why he is known as modern exponent of this theory. Montesquieu ‟ s doctrine, in essence, signifies the fact that one person or body of persons should not exercise all the three powers of the Government viz. legislative, executive and judiciary. In other words each organ should restrict itself to its own sphere and restrain from transgressing the province of the other.
Montesquieu explained the doctrine in its own word they are:
“When the legislative and executive powers are united in the same person, or in the same body or magistrates, there can be no liberty. Again, there is no liberty if the judicial power is not separates from the legislative and executive powers. Where it joined with the legislative power, the life and liberty of the subject would be exposed to arbitrary control; for the Judge would then be the legislator. Where it joined with the executive power, the Judge might behave with violence and oppression. There would be an end of everything were the same man or the same body to exercise these three powers…”
Importance of The Doctrine Of Separation Of Power

The doctrine of separation of power in its true sense is very rigid and this is one of the reasons of why it is not accepted by a large number of countries in the world. The main object as per Montesquieu in the
Doctrine of separation of power is that there should be government of law rather than having will and whims of the official. Also another most important feature of the above said doctrine is that there should be independence of judiciary i.e. it should be free from the other organs of the state and if it is so then justice would be delivered properly. The judiciary is the scale through which one can measure the actual development of the state if the judiciary is not independent then it is the first step towards a tyrannical form of government i.e. power is concentrated in a single hand and if it is so then there is a cent percent chance of misuse of power. Hence the Doctrine of separation of power do plays a vital role in the creation of a fair government and also fair and proper justice is dispensed by the judiciary as there is independence of judiciary.
India: The doctrine of separation of powers has no place in strict sense in Indian Constitution, but the functions of different organs of the Government have been sufficiently differentiated, so that one organ of the Government could not usurp the function of another.
In Indian Constitution there is express provision that “Executive power of the Union shall be vested in the President and the executive power of the State shall be vested in Governor..” (Article 154(1) of
Indian Constitution). But there is no express provision that legislative and judicial powers shall be vested in any person or organ.
Now we have to see what is the real position in India regarding the separation of powers?
President being the executive head is also empowered to exercise legislative powers. In his legislative capacity he may promulgate Ordinances in order to meet the situation as Article 123(1) says “If at any time, except when both Houses of Parliament are in Session, President is satisfied that circumstances exist which render it necessary for him to take immediate action, he may promulgate such Ordinance as the circumstances appear to him to require”.
When Proclamation of emergency has been declared by the President due to failure of Constitutional machinery the President has been given legislative power under Article 357 of our Constitution to make any Law in order to meet the situations. A power has also been conferred on the President of India under Article 372 and 372-A to adapt any Law in country by making such adaptations and modifications, whether by way of repeal or amendment as may be necessary or expedient for the purpose or bringing the provisions of such Law into accord with the provisions of the Constitution.
The President of India also exercises judicial function. Article 103(1) of the Constitution is notable in this connection. According to this Article “If any question arises as to whether a member or either of House of Parliament has become subject to disqualification mentioned in clause (1) of Article 102, the questions hall be referred for the decision of the President and his decision shall be final”. Article 50 lays emphasis to separate judiciary from executive. But in practice we find that the executive also exercises the powers of judiciary as in appointment of judges. (Articles 124, 126 & Article 127). The legislative
(either House of Parliament) also exercises Judicial function in removal of President (Article 56) in the prescribed manner. Judiciary also exercises legislative power, High Court and Supreme Court are empowered to make certain rules legislative in character. Whenever High Court or the Supreme Court

finds a certain provision of law against the Constitution or public policy it declares the same null and void, and then amendments may be incorporated in the Legal System. Some time High Court and
Supreme Court formulate the principles on the point where law is silent. This power is also legislative in character.
Judicial view on the doctrine of Separation of Power
As clearly mentioned about the separation of power there were times where the judiciary has faced tough challenges in maintaining and preserving the Doctrine of separation of power and it has in the process of preservation of the above said Doctrine has delivered landmark judgments which clearly talks about the independence of judiciary as well as the success of judiciary in India for the last six decades.
The first major judgment by the judiciary in relation to Doctrine of separation of power was in Ram
Jawaya v state of Punjab. The court in the above case was of the opinion that the Doctrine of separation of power was not fully accepted in India.
Later in I.C.Golak Nath v State of Punjab, Subha Rao, C.J opined that
“The constitution brings into existence different constitutional entitles, namely the union, the state and the union territories. It creates three major instruments of power, namely the Legislature, the Executive and the Judiciary. It demarcates their jurisdiction minutely and expects them to exercise their respective powers without overstepping there limits. They should function with the spheres allotted to them”
In Keshvananda Bharti v Union of India6 the court was of the view that amending power was now subject to the basic features of the constitution. And hence, any amendment tampering these essential features will be struck down as unconstitutional.