This tension in Hayek's thought, between the rationalist advocacy of liberal reform and the anti-rationalist critique of all social reconstruction, has inclined one commentator to describe his political theory as 'Utopian non-engineering'. While the word 'Utopian' might exaggerate a little the rationalist character of his thought, this term captures well the unstable nature of the Hayekian system of ideas. For, in the end, a Humean scepticism about the powers of reason is incompatible with a Kantian insistence on the priority of rationally justifiable principles. Hayek has tried to cast himself in the image of that most improbable of creatures: the principled sceptic.