It's impossible to know in this world whether one is truly happy. Most of us who think we are can easily imagine a greater happiness by changing our lot in some way; how many times have you heard people say - 'I'd be happier if I was thinner', 'if I had won the triple trio', 'if I was in love', 'I wasn't in this job'. The Collins Concise Dictionary defines happy as 'feeling or expressing joy', yet, joy is defined as 'a deep feeling of happiness', so we are no further to understanding whether we have arrived at the blissful state because no one really knows what it is. How much easier it would be if there was a way to measure happiness, a multiple-choice questionnaire perhaps or a test to measure responses such as how often you smile, how upbeat your walk is, or when you last laughed. At the end, someone could pronounce: 'Yes, you have nothing to worry about. You are a happy person.' The happiness issue, or at least the state of being unhappy (as much of society seems to be), attracted the makers of the documentary How To Be Happy (Pearl, 8.30pm). In an attempt to shake off society's lingering feelings of unhappiness and discontent, the BBC's QED team set up its own 'course in happiness', and discovered that indeed there are ways of measuring the sublime state. The aim of the course, which was created with the help of professionals, was not to treat depression but to take a more fundamental approach to the problem, to change deep-seated beliefs and attitudes. Three volunteers began the eight-week course and the cameras follow their progress. The first, Caroline Ponting, gave up her full-time job six years ago to care for her invalid mother. She feels trapped, unable to communicate and lacking in confidence. Private investigator Dawn Harrison left her home town in search of happiness but found she took her problems with her. Based on the University of Ottowa's Affectometer, Harrison is not as unhappy as Ponting but she is not as happy as third volunteer Keith Allen, who gave up his job and girlfriend (but kept his Daimler) in his search for happiness. As part of the course, under the guidance of psychologist Robert Holden, all three have their basic beliefs challenged. Will it make them happy? For those who think happiness is being slim, Movie Magic (Pearl, 8pm) shows us how Hollywood makes its stars gain hundreds of pounds and lose them just as quickly, from bodysuits to prosthetics. The best film tonight is Patriot Games (Pearl, 9.30pm), an adaptation of Tom Clancy's thriller involving the CIA, IRA and British royal family. The actors, who are perfectly cast, include Anne Archer, Patrick Bergin, Sean Bean, Samuel Jackson, James Earl Jones, Richard Harris, James Fox and Polly Walker. Hugh Grant is remarkably good in Maurice (World, 1am), a solid Merchant-Ivory production about a young man (James Wilby) who has to come to terms with his homosexuality when he falls in love with a fellow student at Cambridge. The cast includes Rupert Graves, Denholm Elliott, Simon Callow and a cameo from Helena Bonham Carter. A couple desperate for a child take drastic measures to 'legally' adopt in Saigon Baby (World, 3.20am), a powerful and moving film starring John Hurt and Kerry Fox.