The principle may apply to other forms of differential taxation, e.g., land values, which are not upon immediate income, but fall on future prospects. Where taxes are levied on commodities, the broad principle of an alternative untaxed supply is important. A customs duty on imports balanced by an excise on home produc tion, throws the whole tax (B) as an addition to cost price (A) and the final effect depends upon "elasticity of demand"—if the public will not buy the old quantities at the higher price (A+B) the effect may be to reduce sales which will pass off at a rather lower level C, intermediate between A and (A+B). But, where there is no duty on the home product, the general or broad result is that the foreign exporter needs to add the tax B to his price, the home producer can secure something approximating to A+B, and his trade expands at the expense of the foreigner. This result, again, is materially qualified by elasticity of demand, internal competition, and the degree to which the foreign exporter was mak ing large differential profits which can be cut into before he will relinquish the market. The principle of substitution is operative to a marked extent in controlling incidence. A high tax on tea may encourage the substitution of other beverages. The incidence of death duties is indeterminate—it is described by the Colwyn Committee as follows: On practical grounds, we think it is impossible to say that the incidence of the estate duty is uniform.
If a testator has consciously stinted his expenditure and saved more year by year than he would otherwise have done, regarding the difference solely as a piling up of the tax against the day of his death, it is hard to deny that the incide ce is upon him during his life.
On the other hand, the feelings and action of the testator have not been influenced in any direction by the prospect of the duty, the successor is the only person who suffers and the only person to whom the incidence can well be assigned. . . . When one compares the income tax with the estate duty, regarding the latter as a kind of postponed income tax, one sees clearly the solidarity of the interests of predecessor and successor. The income tax, in a concealed way, hits the taxpayer's son as well as the taxpayer himself, and may hit him just as severely. But the damage is separated by a time-gap. In the case of the estate duty the time-gap is bridged, and the damage is at once apparent. On the whole, we think we have good support for giving primary but not exclusive place to the notion that the incidence of the duty is on the predecessor.
The incidence of local rates on building rentals was highly debated for many years and is not finally determinable. At one time, it was said that all such taxation was thrown off upon ground rents, which could, and would, be pro tanto higher if local rates did not exist. But the reasoning upon which this was based
would have applied almost equally to a reduction in the price of a "hair cut." It has to be realized that a large part of local rating is payment for value received (by the tenant) and also that local rating acts as a very rough (unshif table) income tax.