The traditional understanding of broad-based tax systems contrasts an income tax with all forms of a consumption tax. The income tax, alone, includes the yield to capital in its base; consumption taxes do not. Simple financial analysis demonstrates the equivalence of the two most common classes of consumption taxation - prepaid, or wage-based, and postpaid, or sales taxes - under certain assumptions, most importantly including constant tax and interest rates between the periods in the model. Advocates of redistributive taxes insist on both progressive rates and an income base, in large part to tax the yield to capital; opponents clamor for flat-rate consumption taxes, often invoking Mill's celebrated argument against the income tax's double taxation of savings to support their case. Once progressivity is presumed, however - as its enduring popular appeal suggests it ought be - the traditional understanding is flawed. Asking a different timing question, when, in a taxpayer's flow of funds, ought progressive taxes be imposed?, casts tax systems in a new light. The present tax system emerges as an onerous wage-based one. A progressive cash-flow consumption tax, in contrast, emerges as the best - most consistent and principled - tax on the yield to capital, under just the conditions in which it is fair and appropriate to tax such yield. This gives a further reason to support a progressive cash-flow consumption tax, sounding in reasons familiar to income tax supporters. A consistent progressive cash-flow consumption tax will lower the burden of taxation when capital transactions (borrowing, saving, and investing) are used to smooth labor earnings within or between lifetimes (or taxpayers), and will increase the burden of taxation when capital transactions are used to enhance labor earnings within or between lifetimes (or taxpayers). Critical reflection based on a near century of experience reveals such a tax to give form to attractive normative ideals. The new understanding helps to show that the traditional and most common arguments for consumption taxation are not compelling. The best, most appealing case for a consumption tax does not rest on simple horizontal equity models, nor on claims about the economic, consequentialist importance of savings on an individual or an aggregate social level. Rather it is claims of fairness, in a social contractarian sense in the manner of John Rawls and other liberal theorists, that argue for a properly designed consumption tax - in part precisely because of the way such a tax sometimes but not all the times burdens capital and its yield, and in greater part because such a tax points the way towards greater, more meaningful progressivity in tax. The new understanding of tax yields important insights into pressingly practical matters of tax policy and design, and opens up an important window to critique contemporary trends in tax reform. The battle in tax policy should not be over income versus consumption taxation - as it has been for centuries - but rather over what kind of consumption tax to choose. Failure to address this question head-on has led tax policy to move, seemingly inexorably, towards the wrong choice, with the fate of progressive, redistributive taxation hanging in the balance
