Fourteenth Amendment, Section 1:
All persons born or naturalized in the United States, and subject to the jurisdiction thereof, are citizens of the United States and of the State wherein they reside. No State shall make or enforce any law which shall abridge the privileges or immunities of citizens of the United States; nor shall any State deprive any person of life, liberty, or property, without due process of law; nor deny to any person within its jurisdiction the equal protection of the laws.
A state may tax tangible property located within its borders (either directly through an ad valorem tax or indirectly through death taxes) irrespective of the residence of the owner. 1 By the same token, if tangible personal property makes only occasional incursions into other states, its permanent situs remains in the state of origin, and, subject to certain exceptions, is taxable only by the latter. 2 The ancient maxim, mobilia sequuntur personam, which originated when personal property consisted in the main of articles appertaining to the person of the owner, yielded in modern times to the
law of the place where the property is kept and used. The tendency has been to treat tangible personal property as
having a situs of its own for the purpose of taxation, and correlatively to . . . exempt [it] at the domicile of its owner. 3
Thus, when rolling stock is permanently located and used in a business outside the boundaries of a domiciliary state, the latter has no jurisdiction to tax it. 4 Further, vessels that merely touch briefly at numerous ports never acquire a taxable situs at any one of them, and are taxable in the domicile of their owners or not at all. 5 Thus, where airplanes are continually in and out of a state during the course of a tax year, the entire fleet may be taxed by the domicile state. 6
Conversely, a nondomiciliary state, although it may not tax property belonging to a foreign corporation that has never come within its borders, may levy a tax on movables that are regularly and habitually used and employed in that state. Thus, although the fact that cars are loaded and reloaded at a refinery in a state outside the owner’s domicile does not fix the situs of the entire fleet in that state, the state may nevertheless tax the number of cars that on the average are found to be present within its borders. 7 But no property of an interstate carrier can be taken into account unless it can be seen in some plain and fairly intelligible way that it adds to the value of the road and the rights exercised in the state. 8 Or, a state property tax on railroads, which is measured by gross earnings apportioned to mileage, is constitutional unless it exceeds what would be legitimate as an ordinary tax on the property valued as part of a going concern or is relatively higher than taxes on other kinds of property. 9