The main problem with the doctrine is that it demands absolutes. Bush is notorious for reflecting a simple black-and-white worldview in his speeches and public pronouncements. The world contains good guys and bad guys, us and them. The bad guys might be states or they might be non-state actors, but they all have one thing in common: they threaten our interests and mean us harm. They must therefore be dealt with mercilessly before they have the chance to strike. Yet if there is one thing we have learned from the Iraq conflict, it is that intelligence is rarely black and white. Instead it expresses shades of grey, percentages and probability over which careful judgements must be made. Very often, intelligence will prove nothing, and smoking guns are a rather rare phenomena. But to convince a sceptical media and voters that a pre-emptive strike is justified, the case must be proved - and it must be done in advance, before any evidence can actually be gathered.
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