Importantly, and largely not understood by most, that same concept applies to income.

FORBES: Keynes Would Not Raise Taxes Today

When you in your 30s and 40s most folks are raising kids, and there goes the whole concept of discretionary income.

FORBES: You (And Your Company) Are Unique. So Why Is Your Marketing Strategy The Same As Everyone Else?

The concept of a minimum income standard (MIS) was introduced by the Joseph Rowntree Foundation (JRF) four years ago - I wrote about it here.

BBC: Do you live above the bread, butter and jam line?

It's about time the concept of taxing all income at a single rate, which presidential candidate Steve Forbes and then-House Majority Leader Dick Armey broached a decade ago, once again takes center stage.

WSJ: The World Is Flat

PwC invented this concept by dividing adjusted gross income by federal income taxes shown on the returns.

FORBES: East of Eden: Mitt Romney's 2011 Returns

For Romney, who probably knows more about personal income taxes than most Americans, the concept behind his statements is not only a flim-flam, it implies that somehow half the population is not working and on the dole.

FORBES: Time to Occupy Mitt Romney

The concept of Roth IRAs: You pay your income tax going in, rather than going out.

FORBES: Rothify now

This week there was talk that Grover Norquist mooted the concept of swapping a carbon tax for a reduced income tax, a position he summarily reversed the following day under pressure from the energy lobby.

FORBES: A New Report on Climate Change: The World Bank Tries to Wake Us Up

This concept is embodied in U.S. economic policy through the Earned Income Tax Credit, introduced in 1975 under Republican President Gerald Ford.

FORBES: Minimum Wage Pits Obama Against Keynes