Its not often that you get a film which provides a survey of a fundamental intellectual distinction in English law: nor is it often that such a film is set in a Japanese prison camp during World War Two. Bridge on the River Kwai however is the first and is set in the latter locale. It is about the distinction between equity- the law of right reason- and law. The film is suffused with law. Its basic situation is legal. Colonel Nicholson leads a detatchment of British soldiers into a Japanese prison camp- there Colonel Saito the Japanese commander orders the men to start buildiing a bridge across the River Kwai. Saito tells Nicholson that he must work alongside his men, Nicholson cites the Geneva Convention and resists this order. Eventually Saito desperate as he cannot command Nicholson's men brings the British colonel back to command his troops, conceding that no officer need work on the bridge. Secondly Nicholson now makes his decision to build the bridge- he makes the decision to relocate the bridge to a more secure point, to put his better engineers in charge and to drive the British soldiers on to work on the bridge. In that he is successful and he produces a bridge for the Japanese which excells the bridge that they might have built themselves.
The plot therefore is dual- but both plots are based around a conflict of laws, a conflict between legality and equity. In the first case Saito is legally entitled to do what he does. He does not believe in the Geneva Convention but in the cult of Bushido. For him Nicholson and his British officers are cowards who do not merit any consideration- they have led their men to defeat and so must suffer alongside the men the humiliation of defeat. The Geneva Convention for him is no law- just as it was not for the Japanese who did not sign the convention until after World War Two. However during the course of the project he comes to realise that building the bridge will be impossible without Nicholson's cooperation. The Colonel manages to outlast Saito's tortures, manages to cope with them and survive. Furthermore his men are demoralised and will not work for Japanese officers, they mar more than they make and whilst Saito cannot discipline them, if they die there will be no bridge, he also must get them to work more efficiently. It is reason rather than legality therefore which suggests to him the milder treatment for the Colonel and his officers: Saito gets what he wants through following a rule of equity, showing sympathy rather than cruelty and motivating the men to work properly.
Colonel Nicholson faces the other side of this dilemma. From the first moment we see him talk in the camp, we see that he is an enthusiast for law. He will not escape, he tells Commodore Sheers, an American in the base, because his superiors ordered him to surrender: to escape would be to disobey their order. The Colonel believes fundamentally that he is there to make sure that his men obey their duty as narrowly and legally considered. They are prisoners of the Japanese, prisoners are supposed to work for their keep and therefore he makes even the sick work. He raises the bar that they have to work towards- raising the levels of their output. He reccomends more effective methods to the Japanese, partly because he wants to be seen to be obeying them and wants it to be seen that British methods are better than Japanese ones. Partly though Nicholson believes that without law there is no civilisation: it is not for him to question the law merely for him to implement it. What that ends up doing is constructing a bridge that will take Japanese trains forwards to reinforce the frontier. Nicholson ends up, as his physician tells him he is, as a collaborator.
Saito and Nicholson go through the same journey in the film. You can see this in their attitude to men: both of them compel the sick to work, both of them compel men to work harder than they might, both of them believe in discipline, both of them are officers. There are illuminating conversations midway through the film in which we sense that they are both frustrated that the ultimate result of their efforts has not been greatness or tangible success but mid ranking mediocrity. Neither can see why. Saito and Nicholson only realise towards the end that their fatal flaw is to exchange judgement for a rule: in Saito's case the rule of what he is allowed to do brutally to his prisoners, in Nicholson's the rule of what prisoners are expected to do for their commanders. Both of them are task orientated: Saito wants the bridge done, to hell with the prisoners. Nicholson wants to demonstrate the bridge will be finished quicker, to hell with the ultimate aim that the bridge is there for. Both of them have their heads down scanning the ground in such a way that they lose sight of the ways that their actions are counter productive. When Nicholson's physician derides them as mad, this is what he means- they have lost sight of their direction in the world, focussed as they are on an immediate goal.
As I said above what this ressembles is the debate about equity and legality in law- whether the important thing about law is what it is designed to do- justice- or what it is- law. Neither Nicholson or Saito realise what the equity of their own situation is before they lose control of it: one of them loses his life, the other loses his camp and both lose what they lose because ultimately they forgot the real purpose of their activity and concentrated on the quickest way to acheive their duty.