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.
- from the United States Declaration of Independence, July 4, 1776.
This is an interesting concept. I agree that the right to one's life and liberty are self-evident but what does the "pursuit of happiness" even mean?
There is a common law precept which suggests that people have the right to "quiet enjoyment" of real property (ie physical things which one owns) and the undisturbed use of those things (which also includes land), which to be honest, I find quaint and maybe a little antiquated in tone but the "pursuit of happiness" itself, I still find to be baffling.
Happiness is a sometimes fleeting thing. One's circumstances can very easily impose a state of unhappiness upon one, and so if we assume that being happy all the time is an impossibility (or perhaps a sign of madness), then maybe the pursuit of happiness is not quite so silly.
Then again, living in such a way so as to provide only for one's happiness is a selfish way to live and the pursuit of happiness could also be taken to mean that we have a right to indulge in hedonism.
It is worth considering though, that the Declaration of Independence itself is not a legal document, nor was it ever formally presented to the authorities which it was complaining against (specifically the King), so it is more like a declaration to one's self, or a self-affirmation that the writers were doing the right thing in committing many lives in sacrifice to the creation of a new nation.
Maybe the writers were far more practical in their intent. It could be for instance that the writers saw that the "pursuit of happiness" referred to the right that the people and indeed thirteen states had to pursue their own self-determination; that fits in with the spirit of the document. An older form of the word means to enjoy a state of good fortune, or prosperity. The impost of what the thirteen states saw as burdensome taxation was an anathema to the quiet enjoyment of the prosperity which was produces, which also ties in with the other idea that happiness is a state of well-being. Having one's happiness disturbed by an overseas power especially would certainly give cause for any nation to fight for their right to self-determination and existence, and so again, that also makes a degree of sense.
In the end, Thomas Jefferson wrote what I think is still one of the most praiseworthy documents ever conceived in the English Language, even if the actual intent of this phrase is unclear with the passing of 237 years. In the context of the Revolutionary War it would have given Americans hope and cheer, so maybe it does contribute in its own way to the "pursuit of happiness".