Jefferson borrowed the expression from an Italian friend and neighbor, Philip Mazzei,[3] as noted by Joint Resolution 175 of the 103rd Congress as well as John F. Kennedy in "A Nation Of Immigrants."[4][5]
The opening of the United States Declaration of Independence written by Thomas Jefferson in 1776, states as follows:
We hold these truths to be self-evident, that all men are created equal, that they are endowed by their Creator with certain unalienable Rights, that among these are Life, Liberty, and the Pursuit of Happiness. That to secure these rights, Governments are instituted among Men, deriving their just powers from the consent of the governed;[6]
The same concept appears in the Massachusetts Constitution of 1780, which was written mostly by John Adams.[7] The Declaration of Rights of the Inhabitants of the Commonwealth of Massachusetts which opens that constitution states:
Article I. All men are born free and equal, and have certain natural, essential, and unalienable rights; among which may be reckoned the right of enjoying and defending their lives and liberties; that of acquiring, possessing, and protecting property; in fine, that of seeking and obtaining their safety and happiness.[8]
The plaintiffs in the cases of Brom and Bett v. John Ashley and Commonwealth v. Nathaniel Jennison argued that this provision abolished slavery in Massachusetts.[9] The latter case resulted in a a "sweeping declaration . . . that the institution of slavery was incompatible with the principles of liberty and legal equality articulated in the new Massachusetts Constitution".[10]
These statements illustrated the idea of natural rights, a philosophical concept of the Enlightenment and many of the ideas in the Declaration were borrowed from the English liberal political philosopher John Locke. Locke, however, referred to "life, liberty and Property" rather than the pursuit of happiness.[11]
The phrase has since been considered a hallmark statement in democratic constitutions and similar human rights instruments, many of which have adopted the phrase or variants thereof.