The expression " double taxation" appears almost self-explanatory, yet it may have a number of applications. In general, it refers to the levy and collection of two taxes, the burden of which falls upon the same base. Such an occurrence immediately appears to be unjust. This, however, is not necessarily true. If a tax were levied upon all property, for example, and then a tax were levied upon the income from this property, it might be called a case of double taxation. It would be unjust, however, only if some classes of the property owners were subject to the income tax while others were not. Under such conditions the income tax would be a discriminating tax. When two taxes are levied alike upon all classes, the result is the same as if a higher property or a higher income tax had been used. The use of the expression " double taxation," however, usually implies an injustice, so that it might be well to use another expression, say "dual taxation," to apply to the levy of two taxes upon the same base when no injustice is perpetrated.

Many cases of double taxation and even multiple taxation arise, however, which are clearly unjust because of the unequal burden which they impose upon different classes of property. Cases of this nature arise within a particular taxing jurisdiction, and to a magnified degree where competing jurisdictions are concerned. Double taxation arises in the first case from the attempt to tax land and factories and from the attempt at the same time to tax evidences of claims upon this property. The same situation arises between competing jurisdictions because of the individual code of tax laws which each jurisdiction has adopted, with little regard for interjurisdiction comity. The states, in particular, have been anxious to extend their jurisdiction over as much taxable property as possible. This ambition has often been so keen that the legislatures, and even the courts, have frequently lost sight of what would ordinarily be called fair play. The result is that tax systems exist that will not stand the requirements of justice under the present industrial organization.

• Place of Levy. - Much litigation has arisen over the proper situs or location of property for purposes of assessment, and many unsatisfactory decisions have been rendered. When securities are assessed by the officials of one jurisdiction, and the property in which these securities represent but an interest is assessed in another jurisdiction, a part of the tax is clearly an unjust burden. A share of stock of a corporation chartered in New Jersey, and owned by a citizen of Pennsylvania, who is temporarily living in Maryland, should obviously not be taxed in the three different states; yet such attempts have been made, and marked injustice often arises. Modern industry is so expansive that a single business unit may be represented in a number of tax districts, which creates the possibility of a multiplication of taxes.

Many factors have been used by the different states in determining the proper principle upon which to make the tax levy. Some use citizenship as the proper criterion upon which to make the levy, while others use domicile, situs of property, situs of securities, or other factors, until it is possible to have taxes levied by as many as a half dozen states upon the same taxable base. If every jurisdiction should decide upon the same principle, then there would be little need to raise the question of double taxation. The disinclination to do this, however, makes the problem a serious one.

The principle of citizenship is one that is frequently followed in determining where taxes should be paid. The United States, for example, levies an income tax upon its citizens no matter where they are located. Citizenship, no doubt, was at one time the important consideration, and still has some claim in a state's right to levy taxes. Under the organization of industry as it is at present, however, other factors must be given consideration. A man, for example, may be a citizen of one taxing district, may be a permanent resident of another, may for the time being be living in still another, and have all his property in the form of a corporate business located in a fourth district, the charter of which was taken out in still another district. Each of the districts has some claim to tax the individual, while evidently there is but one property upon which the burden of the tax can fall.

It may be true that taxes should be paid in more than one district - in fact, it seems reasonable that an individual should pay taxes at least in the district where his property is located and where he has his permanent residence. Yet it does not follow that each of these districts should levy the tax as if its tax were the only one to be levied. It has been suggested that the owner of property should be taxed where his real economic interest is found. The suggestion is good, but to carry it out it would be necessary to secure the proper apportionment of the tax burden among the districts where the interests of the indvidual lie, and to get each district to respect the rights of the other taxing units. Until this is accomplished a large amount of injustice may be expected in the taxes levied by competing jurisdictions.

Bases for tax levies are sometimes arbitrarily made. A good example of this situation is the taxation of the shares of stock of national banks. These shares must be assessed to the owner at his place of residence, but for purposes of taxation his residence shall be considered in the district where the bank is located. A man living in California, who owns shares of stock in a national bank in New York, would be assessed and taxed on the shares as if he lived in New York.