An income tax is a tax levied on the financial income of persons, corporations, or other legal entities. Various income tax systems exist, with varying degrees of tax incidence. Income taxation can be progressive, proportional, or regressive. When the tax is levied on the income of companies, it is often called a corporate tax, corporate income tax, or profit tax. Individual income taxes often tax the total income of the individual (with some deductions permitted), while corporate income taxes often tax net income (the difference between gross receipts, expenses, and additional write-offs). Public finance is a field of economics concerned with paying for collective or governmental activities, and with the administration and design of those activities. The field is often divided into questions of what the government or collective organizations should do or are doing, and questions of how to pay for those activities. The broader term (public economics) and the narrower term (government finance) are also often used.