There may be people with higher IQs than John Maynard Keynes but when it comes to human affairs, I doubt there has been a greater thinker in recent memory than the great economist, probability theorist and philosopher. Many sayings have been attributed to him, but the following one has been my favourite, mostly because I have rarely been able to do so myself: 'When the evidence proves I'm wrong, I change my mind. What do you do, sir?'

So a tip of the hat is due to two men who have changed their minds in the debate on two important issues - breaking up the big banks and climate change - over which they have had great influence: Sandy Weill and Richard Muller. Weill has been one of the greatest - or worst - Western bankers of the second half of the 20th century, depending on your perspective. The creator of the modern Citigroup, Weill pioneered the 'supermarket' model - a one-stop shop of financial and banking services - which has led to the creation of the too-big-to-fail banks. But now, after two of his famous proteges - Chuck Prince, formerly of Citigroup, and Jamie Dimon, of JPMorgan - have run into their own Waterloos, Weill has thrown in the towel and announced on CNBC that he is now in favour of breaking up the big banks. It's somewhat like the pope announcing that condoms are now acceptable.

In a similar vein, Muller has been one of the few mainstream scientists who have disputed the reality of climate change. For being a sceptic with impeccable academic credentials - he is a respected physics professor at the University of California, Berkeley - his research has been funded by right-wing tycoons in the US.