It is evident that no exact gauge of ability is at hand. If the actual income of every citizen could be distinctly known, and the burdens of a dependent household clearly expressed, a basis for equal sacrifice, so far as wealth is concerned, might be reached. But no such basis has been or can be actually found. If found, it would not give an accurate gauge of sacrifice, because the actual wants for comfort of different individuals are so widely varied. Two distinct approximations toward this equity are found. The first is in the total annual consumption of the individual taxpayer, especially of such articles as meet wants above the mere maintenance of healthy existence. In this the government assumes that all will spend according to their ability. The second is in a total accumulation of property. In this the government assumes that every man saves for future consumption all that he gains above his present needs. Both assumptions are untrue in individual cases, and only approximately true anywhere. In many instances the expenditure of a given year upon more continuous wants than ordinary, like a home or farm buildings, will count also as wealth laid by. So, in any combination of the two systems of taxation, the more thrifty and far-seeing will bear a double burden. Yet even this combination may not transgress the rule of equity, since such foresight is itself proof of ability. To this first principle of equity we may add others, less fundamental, but equally important in practice. _Taxes must be sufficiently definite to be understood and provided for by every taxpayer._ This is needed for maintaining the interest of every citizen in both the necessity and the economy of public expenditures. _Taxes must be so levied and collected as to be conveniently paid._ This means that private enterprise shall be hindered as little as possible in making assessments, and that times and places of collection shall be suited to the convenience of taxpayers. _The collection of taxes must be by such methods as will involve least outlay, either in salaries of officials or in machinery of the collecting process._ These four principles of taxation were announced by Adam Smith more than a hundred years ago, and have commended themselves to students of the subject ever since. It is evident that the last three are more explicit methods for carrying out the first. Most briefly stated; they imply equity, definiteness, convenience of paying, and economy in collecting.