In a preamble to the Declaration of Independence, US President Thomas Jefferson wrote; 'all men are created equal and independent, and that from that equal creation they derive rights, among which are the preservation of life, and liberty, and the pursuit of happiness'.
In 'The Pursuit of Happyness', released this week, Chris Gardener (played by Will Smith) ponders this statement and wonders if happiness is something we spend our lives pursuing rather than something which we might actually attain.
'The Pursuit of Happyness' tells the true story of Chris Gardener, a young father who is left to look after his four year old son when the boy's mother walks out on them both.
Chris has been working as a salesman but when he finds it hard to make ends meet he goes in search of a proper, full-time job.
A leading firm of San Francisco stock-brokers, Dean Whitter, is offering internships to twenty young men and, after a lot of effort, Chris earns himself a place on the scheme only to find out that the six month internship is unpaid, and there is no guarantee of a job at the end of it.
Determined to provide a better life for his son Christopher (played by Smith's real life son Jaden) Chris takes a big risk and signs up to the internship, even though he is about to be evicted from his apartment and can barely afford to feed himself or his young son.
Gardener has to juggle work with caring for his son, which means he can't put in the long hours that the others on the internship can. But he finds ways to maximise his output at work, including not hanging up the phone between calls and not drinking water so he doesn't waste time going to the bathroom.
When the pair are evicted from their apartment they move into a motel but get kicked out of there when they can't pay for their room.
The lowest point comes when they have to spend the night in a train station toilet. But even though Chris is at breaking point he never lets his son know just how bad things have got.
Chris even goes hungry a few nights as he only has enough money to feed his son.
Set in San Francisco in 1981 'The Pursuit of Happyness' provides Will Smith with one of his most emotionally charged, and understated, roles to date and the actor puts in one of the finest performances of his career as a single parent who must believe in himself if he is to provide for himself and his young son.
These two have a great on-screen chemistry here (no doubt something to do with their real life relationship) and young Jaden puts in an exceptional debut performance as the young boy whose mother walks out on him and has to spend nights in motels, hostels and homeless refuges with his dad.
After saying all this, it should be pointed out that this is not a sad movie. Quite the contrary, this is a film full of happiness, resilence and, most importantly, hope and belief.
Gardener knows that he is intelligent, even though he mightn't have the qualifications to prove it. And he knows that, through hard work and determination - and a bit of luck - he will come through this on the winning team.
'The Pursuit of Happyness' is a feel-good movie from start to finish and the theme underlying this real life story is the chasing of the American dream. And even though the movie promotes the notion that anything in life is possible if you have belief and work hard the film somehow manages never to descend into out and out preaching.
If you fancy something with a big dose of sentiment and some fine performances to boot 'The Pursuit of Happyness' is well worth a look.