is core to the notion of “life, liberty and the pursuit of happiness” in the Declaration of Independence

the idea that government may never restrict citizens’ liberty

I don't think so. The government can restrict our liberty in certain situations. For instance we can't drive 50 mph in a 30 mph zone.

Human agency

The meaning of those words can be interpreted in many ways. A good explanation of the roots of the idea is here:

http://en.wikipedia.org/wiki/Life,_Liberty_and_the_pursuit_of_Happiness

the concept of American exceptionalism

The phrase "life, liberty, and the pursuit of happiness" is one of the most famous lines from the Declaration of Independence, a document that declared the United States' independence from Britain in 1776. It is considered core to the notion of individual rights and freedoms.

To understand this phrase in the context of the Declaration of Independence, it is necessary to explore its historical background and the philosophical thinking that influenced the Founding Fathers.

1. Historical Background:
The Declaration of Independence was written during a time when the American colonists were dissatisfied with the rule of the British monarchy. They sought to create a society based on the principles of self-governance, freedom, and equality, which they believed were essential for a just and prosperous nation.

2. Influence of Enlightenment Philosophy:
The Founding Fathers, such as Thomas Jefferson, drew inspiration from Enlightenment philosophy, which emphasized reason, individualism, and natural rights. Thinkers like John Locke argued that all individuals possess inherent natural rights, including the rights to life, liberty, and property.

3. Explanation of the Phrase:
a. Life: The right to life refers to an individual's right to exist and enjoy their existence without unwarranted interference. It encompasses the idea that every person has the right to protect their own life and seek safety and well-being.

b. Liberty: Liberty refers to the freedom to act, think, and express oneself without unjust restrictions. It signifies the absence of tyranny or oppression, allowing individuals to exercise their rights and make choices based on their own free will.

c. Pursuit of Happiness: Jefferson replaced John Locke's original phrase of "the pursuit of property" with "pursuit of happiness." Happiness, in this context, does not solely mean fleeting pleasure but encompasses the pursuit of personal fulfillment, prosperity, and well-being.

4. Importance and Interpretation:
The inclusion of "life, liberty, and the pursuit of happiness" in the Declaration of Independence was a significant departure from the traditional justification of political power that was based on divine right or hereditary privileges. It asserted that governments should be based on the consent of the governed, and their primary purpose should be to secure and protect individual rights.

The phrase has been interpreted differently over time, but it serves as a foundational principle for the American political system. It represents the belief that all individuals have the right to live freely, make choices, and seek personal fulfillment, as long as they do not infringe upon the rights of others.

In conclusion, the phrase "life, liberty, and the pursuit of happiness" is a crucial element in the Declaration of Independence. It reflects the underlying principles of individual rights, self-governance, and the pursuit of personal fulfillment that the Founding Fathers believed to be fundamental to a just and free society.