The "pursuit of happiness" is an early example of postmodernism (a.k.a., newspeak[1], or Humpty Dumpty[2] syndrome). The original wording was "pursuit of property", but that wording would have lead to an unfortunate lack of support from certain circles (i.e. the poor majority), so it was reworded to sound more innocuous. This is bog-standard postmodernist behavior: misuse and/or redefine extant terminology not by accident but deliberately, in order to mislead and confuse people into agreeing with you who otherwise don't. Reinhold Neibuhr mastered the technique so well that to this day a lot of folks think he was a Christian theologian, whereas he was in fact a secular philosopher with some really... unusual ideas, ideas that are highly inconsistent with Christianity. A lot of education textbooks make heavy use of this technique also; it's pretty scary if you examine it too closely.

Incidentally, it is generally held to be Ben Franklin who came up with the wording that was ultimately used ("pursuit of happiness"). I'm not sure how we know that, though.

Ώ] From George Orwell.

ΐ] From Lewis Carol.