Final answer:
In the U.S., after the Tax Cuts and Jobs Act of 2017, corporate taxes are of a proportional tax system where the rate is a flat 21% for all corporations, in contrast to a progressive system where rates increase with income.
Step-by-step explanation:
In the U.S., corporate taxes following the passage of the Tax Cuts and Jobs Act of 2017 operate on a proportional tax system. This means the tax rate is the same for corporations regardless of their income. Prior to the act, the U.S. had a progressive tax system, where corporations were taxed at increasing rates as their income increased. However, with the new legislation, the corporate tax rate was set to a flat 21%, which is consistent with the definition of a proportional tax system, as every corporation pays the same share of taxes regardless of how much they earn. To put it into context with another type of tax based on the provided examples, if gifts were taxed at a rate of 10% for amounts up to $100,000 and 20% for anything over that amount, that tax would be considered progressive, because the tax rate increases with the amount of the gift, which means those who give larger gifts would pay a higher percentage in taxes.