This week it was reported that the creditors would offer Greece access to €7.2bn in aid in return for extreme prudence in the longer term, on a take-it-or-leave-it basis. Before risking a “leave it”, they need to ask themselves who it is they want to deal with. An iron law of modern European history runs thus: extreme economics leads to extremist politics. A line can be drawn from the Versailles treaty to the breakdown of the Weimar Republic. Eighty years on, a similar phenomenon is at work. In the course of its depression, Greece has lurched from a social-democrat government to a centre-right one to Syriza – a coalition of leftist parties ranging from Keynesian to Marxist.