Tax cuts and income growth rhetoric

It is incontrovertible that the wealthiest 1% of Americans have benefited from exploding income and collapsing taxes over the previous thirty years.  I haven’t seen anyone deduce how much of the rise in income is attributable to the decrease in taxes; if we know that, we know how much of the income growth has been structural (that which would have occurred if tax rates stayed the same) versus … ephemeral (change in tax codes).  In other words, a 20% decrease in taxes – from 50% to 40%, for argument’s sake – translates directly into a 20% increase in post-tax income.  If the income growth discourse focuses on post-tax income, then I suspect most of the increase in income to the rich is because of lower taxes and not real gains to their income.

It is unclear, as far as I can tell, what figures people are talking about whenever they argue either side of the issue.  If we are talking about post-tax income, which I doubt, than a cursory analysis suggests that correcting inequality simply requires fixing our tax code.  If we are talking about pre-tax income, however, than there are larger structural forces at work.  Arguing for structural forces is not, for me, arguing against higher taxes, but it does suggest that we need a deeper reassessment of several institutions, not just the tax code.

So, does anyone know which form of income people are talking about in these debates?