The definition itself may not be easy to frame and if at all cumbrous, as, for example, in the U.S.A. tariff laws, may be very difficult to apply.
Specific duties have the disadvantage that they cannot well be applied to highly specialized goods without much prior inquiry as to the precise borders of such class and rate, and a very complicated classification would arise. Ad valorem duties permit much wider limits and therefore a smaller number of
Specific and Ad Valorem Duties 71 classes in a tariff. There is consequently much less ground for dispute about the proper rate of duty applicable. Specific duties are more suitable for excise taxation unless the levy is fixed at or near the point of final consumption. An ad valorem excise duty at an intermediate manufacturing stage would place the administration in the position of having to overcome the formidable obstacle of fixing the values of goods which might or might not change ownership as they proceed to the next process. Once a tariff class has been fully defined, specific duties may have an advantage from a revenue collecting standpoint over ad valorem duties by permitting fixed rates to be levied on specialized products. Thus a duty on circular saws can be so subdivided that different specific rates can apply to small changes in diameter although values may not change in the same ratio.