Review Note

If spouses have different incomes and taxation is individual and progressive, then they pay a higher tax than a couple where the incomes of both spouses are the same.

Hence, we have a violation of the principle of global income taxation.

The difference in tax burdens is the distance delta in the next figure.

Non-verifiability:

If some couples can manipulate the assignment of income to their members (as in a family business), individual taxation violates horizontal equity also across couples with the same distribution of true individual incomes, when the tax is progressive.