Enlightenment humanists have maintained, and continue to maintain, that social affairs can be managed with the same rational tools that are used in science. Reason, enlightened by education, can better manage human affairs than the manipulative, irrational fumblings of history's ancient regimes.

The problem is that this has all been tried before, and Reason was found wanting. Kennedy's presidency was famed for its administration of the 'best and the brightest' - highly educated specialists applying 'modern' methods of analysis to the complex problems of foreign policy. Reason and rational analysis were applied with full force to the war in Vietnam. Computer programs were unleashed for diagnosis, with streams of incoming data updating the picture day by day and fresh orders being sent to Generals and Aid programs. And it all failed spectacularly.

Lenin and the Bolsheviks too thought that the application of scientific reason could be applied to modernise the State, with an emphasis on education, careful central planning and staged five year plans. The Jacobins sought to use cold rationality to mould the State when they unleashed The Terror during the French Revolution - Mao sought to do the same with the Cultural Revolution. Pol pot went even further with the concept of Year Zero. And neoconservative planners predicted what they thought would be a rational outcome to the 'liberation' of Iraq.

What all these ideologues had in common was that they sought to simplify complexity. Reason is thought to be the device by which complexity can be understood, reduced and tamed. But complexity, which is to say Reality, cannot be so easily pinned down. It defies simplification. It makes a mockery of even the most elaborate of human ideologies.

Human beings are products of nature, and nature is not reasonable. Human reason is really just a parochial delusion. It is a tool, not a key. A specialised yet limited tool.