With share prices around the world setting new records almost daily, it is tempting to ask whether markets have entered a period of "irrational exuberance" and are heading for a fall. The answer is probably no.

What many analysts still see as a temporary bubble, pumped up by artificial and unsustainable monetary stimulus, is maturing into a structural expansion of economic activity, profits, and employment that probably has many more years to run. There are at least four reasons for such optimism.