In Burnet v. Sanford & Brooks Co., 282 U.S. 359 (1931), the taxpayer argued that a recovery of previously deducted funds should not be income because, seen from a transactional view, no net profits had been realized. The Court framed the issue as whether net profits are to be determined "on the basis of fixed accounting periods, or . . . on the basis of particular transactions of the taxpayer when they are brought to a conclusion." Id., at 363. The answer was unanimous and unflinching: "A taxpayer may be in receipt of net income in one year and not in another. The net result of the two years, if combined in a single taxable period, might still be a loss; but it has never been supposed that that fact would relieve him from a tax on the first, or that it affords any reason for postponing the assessment of the tax until the end of a lifetime, or for some other indefinite period, to ascertain more precisely whether the final outcome of the period, or of a given transaction, will be a gain or a loss. "The Sixteenth Amendment was adopted to enable the government to raise revenue by taxation. It is the essence of any system of taxation that it should produce revenue ascertainable, and payable to the government, at regular intervals. Only by such a system is it practicable to produce a regular flow of income and apply methods of accounting, assessment, and collection capable of practical operation. It is not suggested that there has ever been any general scheme for taxing income on any other basis. . . . While, conceivably, a different system might be devised by which the tax could be assessed, wholly or in part, on the basis of the finally ascertained results of particular transactions, Congress is not required by the amendment to adopt such a system in preference to the more familiar method, even if it were practicable." Id., at 364-365.