Income tax

Tax systems can get out of date. For example, an income tax designed with a rate structure to apply to specified income levels (some type of progressivity goal), will become out of date if the tax brackets are not adjusted for inflation. That is, if individuals with income between $30,000 and $40,000 are to have a 15% rate, they will start to creep into the next higher rate as their income increases with inflation (for example, a person gets a cost-of-living raise), even though their buying power has remained constant (they are really no richer). So, one way to keep the system current, is make an inflation adjustion to the income levels at which each tax rate bracket begins.

What about keeping a tax base current and relevant? That is, enabling a tax base to reflect current ways of doing business and how people live even as things change. That's harder than the rate adjustment which can just be built into the law by having a rule that tells the IRS to adjust the rate structure annually for inflation. Keeping a tax base current and relevant requires regular attention from legislators and making tough decisions. For example, perhaps decades ago it made sense to provide special tax breaks to a particular industry. Yet, if such breaks are not looked at regularly, they remain even when no longer needed. And, it is politically difficult to get a tax break removed once it has been there for a while.