for a fully defined schema In devising a flat tax system, several recurring issues must be enumerated, principally with deductions and the identification of when money is earned. Defining when income occurs Since a central tenet of the flat tax is to minimize the compartmentalization of incomes into myriad special or sheltered cases, a vexing problem is deciding when income occurs. This is demonstrated by the taxation of interest income and stock dividends. The shareholders own the company and so the company's profits belong to them. If a company is taxed on its profits, then the funds paid out as dividends have already been taxed. It's a debatable question if they should subsequently be treated as income to the shareholders and thus subject to further tax. A similar issue arises in deciding if interest paid on loans should be deductible from the taxable income since that interest is in-turn taxed as income to the loan provider. There is no universally agreed answer to what is fair. For example, in the United States, dividends are not deductible but mortgage interest is deductible. Thus a Flat Tax proposal is not fully defined until it differentiates new untaxed income from a pass-through of already taxed income. Policy administration Taxes, in addition to providing revenue, can be potent instruments of policy. For example, it is common for governments to encourage social policy such as home insulation or low income housing with tax credits rather than constituting a ministry to implement these policies. In a flat tax system with limited deductions such policy administration, mechanisms are curtailed. In addition to social policy, flat taxes can remove tools for adjusting economic policy as well. For example, in the United States, short-term capital gains are taxed at a higher rate than long-term gains as means to promote long-term investment horizons and damp speculative fluctuation. Thus, if one assumes that government should be active in policy decisions such as this, then claims that flat taxes are cheaper/simpler to administer than others are incomplete until they factor in costs for alternative policy administration. Minimizing deductions In general, the question of how to eliminate deductions is fundamental to the flat tax design; deductions dramatically affect the effective "flatness" in the tax rate. Perhaps the single biggest necessary deduction is for business expenses. If businesses were not allowed to deduct expenses, businesses with a profit margin below the flat tax rate