Joseph Stiglitz in Evonomics:
In the middle of the twentieth century, it came to be believed that ‘a rising tide lifts all boats’: economic growth would bring increasing wealth and higher living standards to all sections of society. At the time, there was some evidence behind that claim. In industrialised countries in the 1950s and 1960s every group was advancing, and those with lower incomes were rising most rapidly.
In the ensuing economic and political debate, this ‘rising-tide hypothesis’ evolved into a much more specific idea, according to which regressive economic policies— policies that favour the richer classes— would end up benefiting everyone. Resources given to the rich would inevitably ‘trickle down’ to the rest. It is important to clarify that this version of old-fashioned ‘trickle-down economics’ did not follow from the postwar evidence. The ‘rising-tide hypothesis’ was equally consistent with a ‘trickle-up’ theory— give more money to those at the bottom and everyone will benefit; or with a ‘build-out from the middle’ theory— help those at the centre, and both those above and below will benefit.
Today the trend to greater equality of incomes which characterised the postwar period has been reversed. Inequality is now rising rapidly. Contrary to the rising-tide hypothesis, the rising tide has only lifted the large yachts, and many of the smaller boats have been left dashed on the rocks. This is partly because the extraordinary growth in top incomes has coincided with an economic slowdown.