“ A special application is to a tax, a payment due to the revenue of a state, levied by force of law. Properly a “duty” differs from a “tax” in being levied on specific commodities, transactions, estates, &c., and not on individuals; thus it is right to talk of import-duties, excise-duties, death- or succession-duties, &c., but of income-tax as being levied on a person in proportion to his income. ”

“ That a father and his children have mutual duties implies that there are moral laws regulating their relationship; that it is the duty of a servant to obey his master within certain limits is part of a definite contract, whereby he becomes a servant engaging to do certain things for a specified wage. ”