Which type of tax law provision should be more stable and less uncertain as to its future application: a provision relating to the proper measurement of taxable income or a provision designed to encourage individual taxpayers to engage in a certain economic behavior?

Provisions which relates to a proper taxable income measurement are more likely to be a part of fundamental structure of a law than provisions which is designed to affect the economic behavior. The provisions which affect economic behavior reflects the fiscal policies which may change with each new Presidential administration. Hence, they are not stable and more uncertain than the provisions relating to income measurement.