In economics, a duty is a kind of tax, often associated with customs, a payment due to the revenue of a state, levied by force of law. It is a tax on certain items purchased abroad. Properly, a duty differs from a tax in being levied on specific commodities, financial transactions, estates, etc., and not on individuals; thus it is right to talk of import duties, excise duties, death or succession duties, etc., but not of income tax as being levied on a person in proportion to his income.