While the Constitution grants Congress the power to tax income, it does not define the term.

b$.$ The Supreme Court has held that there is no income subject to tax until the taxpayer has recovered the capital invested.

c$.$ Economists measure income $($economic income$)$ by first determining the fair market value of the individual's net assets $($assets minus liabilities$)$ at the beginning and end of the year $($change in net worth$).$

d$.$ Accounting and tax rules regarding income are the same.

e$.$ The accounting concept of income is founded on the realization principle.

f$.$ Gross income is not limited to cash received.