... which means that earnings growth has not been a factor behind the stock market's recent ascent to all time highs. As a result, the conventional explanation to justify the S&P trading just shy of 2,200 is that the market has been the beneficiary of unprecedented multiple expansion. To be sure, as Goldman recently opined, the median stock multiple has never been more overvalue.

Indeed, if one left it at that, the answer would not be exactly wrong, however there is one more factor which is rarely discussed, and which - according to Deutsche Bank - explains virtually the entire equity rally of the past four years: the collapse of the equity risk premium as a result of plunging bond yields, which as a reminder, is the direct pathway by which central banks operate, by monetizing government, and now corporate, debt.