In the 1927 case National Life Insurance Company v. United States, the Supreme Court ruled on a dispute involving income tax deductions. The National Life Insurance Company had claimed certain deductions for payments made to policyholders as dividends from its surplus and premium refunds. However, these were disallowed by the Commissioner of Internal Revenue who argued that they did not constitute "losses incurred" under section 234(a)(5) of the Revenue Act of 1918 and thus were not deductible expenses in computing net income for federal taxation purposes. The court sided with the government's interpretation, holding that such returns to policyholders are essentially part of an insurance company’s operating costs rather than losses or rebates due to overcharges. Therefore, they could not be deducted as 'losses' under existing tax law provisions at that time. This decision clarified how life insurance companies should treat dividend payments and premium refunds in their financial accounting practices for tax purposes - reinforcing that these amounts are considered regular business expenses rather than extraordinary losses.

In the dissenting opinion for National Life Insurance Company v. United States, Justice Oliver Wendell Holmes Jr. disagreed with the majority's interpretation of "income" under the Sixteenth Amendment and its application to life insurance companies' reserves. He argued that these reserves should not be considered as income because they are essentially liabilities - funds set aside to pay future claims, rather than profits or gains realized by the company. According to him, treating them as taxable income would distort their economic reality and unfairly burden insurance companies compared to other businesses which do not have such obligations. Furthermore, he believed that this interpretation was inconsistent with previous court decisions on similar issues and could lead to arbitrary results in different cases depending on how various types of business reserves are classified for tax purposes.