This might help.
With my own clarifications in brackets, I would point out that the Supreme Court noted that Frank Brushaber's propositions were...
so intermingled as to cause it to be difficult to classify them. We [The Court} are of opinion, however, that the confusion [by Frank Brushaber] is not inherent, but rather arises from the [erroneous] conclusion [by Mr. Brushaber] that the 16th Amendment provides for a hitherto unknown power of taxation; that is, [the erroneous assumption that the 16th Amendment itself grants] a power to levy an income tax which, although direct, should not be subject to the regulation of apportionment applicable to all other direct taxes.
And the far-reaching effect of this erroneous assumption [by Mr. Brushaber] will be made clear by generalizing the many contentions advanced [by Frank Brushaber] in argument to support it, as follows:
(a) [Frank Brushaber erroneously argues that] The Amendment authorizes only a particular character of direct tax without apportionment, and therefore if a tax is levied under its assumed authority which does not partake of the characteristics exacted by the Amendment, it is outside of the Amendment, and is void as a direct tax in the general constitutional sense because not apportioned. [erroneous]
(b) [Frank Brushaber erroneously argues that] As the Amendment authorizes a tax only upon incomes 'from whatever source derived,' the exclusion from taxation of some income of designated persons and classes is not authorized, and hence the constitutionality of the law must be tested by the general provisions of the Constitution as to taxation, and thus again the tax is void for want of apportionment. [erroneous] [In other words, Frank Brushaber argues that for a tax statute to be valid, it must not provide any exclusion of income of any person or class or persons. Frank Brushaber argues that for an income tax to be valid under the Amendment, it must tax all income from whatever source derived by all taxpayers, with no exceptions. Frank Brushaber argues that if an income tax law does not tax all income from whatever source without any exclusions, etc., then that tax cannot be judged by the Amendment, and must be judged by the original provisions of the Constitution and must therefore be apportioned to be valid and, since the tax is not apportioned, the tax must be invalid]
(c) [Frank Brushaber erroneously argues that] As the right to tax 'incomes from whatever source derived' for which the Amendment provides must be considered as exacting intrinsic uniformity, therefore no tax comes under the authority of the Amendment not conforming to such standard, and hence all the provisions of the assailed statute must once more be tested solely under the general and pre-existing provisions of the Constitution, causing the statute again to be void in the absence of apportionment. [erroneous] [Frank Brushaber erroneously argues that Sixteenth Amendment power requires intrinsic uniformity, not merely geographical uniformity, and that therefore all the provisions of the tax statute must be judged by the Amendment, and must be judged by the original provisions of the Constitution and must therefore be apportioned to be valid and, since the tax is not apportioned, the tax must be invalid.]
(d) [Frank Brushaber erroneously argues that] As the power conferred by the Amendment is new and prospective, the attempt in the statute to make its provisions retroactively apply is void because, so far as the retroactive period is concerned, it is governed by the pre-existing constitutional requirement as to apportionment. [erroneous] [Frank Brushaber argues that the statute’s retroactive provisions are invalid because the Amendment is new and prospective, and the statute must be governed by the original provisions of the Constitution and must therefore be apportioned to be valid and, since the tax is not apportioned, the tax must be invalid.]
But it clearly results that the proposition [by Frank Brushaber] and the [above listed erroneous] contentions under it [i.e., under Mr. Frank Brushaber’s proposition], if acceded to, would [incorrectly] cause one provision of the Constitution to destroy another; that is, they [Mr. Frank Brushaber’s erroneous contentions] would result in bringing the provisions of the Amendment exempting a direct tax from apportionment into irreconcilable conflict with the general requirement that all direct taxes be apportioned. Moreover, the tax [supposedly] authorized by the Amendment, being [supposedly] direct, would not come under the rule of uniformity applicable under the Constitution to [taxes] other than direct taxes, and thus it would [supposedly] come to pass [under Frank Brushaber's theory] that the result of the Amendment would be to authorize a particular direct tax not subject either to apportionment or to the rule of geographical uniformity, thus giving power to impose a different tax in one state or states than was levied in another state or states. This [erroneous] result, instead of simplifying the situation and making clear the limitations on the taxing power, which obviously the Amendment must have been intended to accomplish, would create radical and destructive changes in our constitutional system and multiply confusion.
But let us[,] by a demonstration of the error of the fundamental proposition [by Mr. Brushaber] as to the significance of the Amendment[,] dispel the confusion necessarily arising from the arguments [by Frank Brushaber] deduced from it.
[ . . . ]
In fact, the two great subdivisions [that is, direct taxes, and excises (or indirect taxes)] embracing the complete and perfect delegation of the power to tax and the two correlated limitations [apportionment for direct taxes, and geographical uniformity for indirect taxes] as to such power were thus aptly stated by Mr. Chief Justice Fuller in Pollock v. Farmers' Loan & T. Co. 157 U. S. supra, at page 557: 'In the matter of taxation, the Constitution recognizes the two great classes of direct and indirect taxes, and lays down two rules by which their imposition must be governed, namely: The rule of apportionment as to direct taxes, and the rule of uniformity as to duties, imposts, and excises.'
If I recall correctly, some tax protesters have argued that the holdings in
Brushaber and other cases somehow cannot be the law because the Court was concerned about
one provision of the Constitution destroying another. In some cases, the argument seems to be that an income tax is a direct tax and that the Sixteenth Amendment cannot modify the original text of the Constitution (requiring apportionment of direct taxes) because that treatment would "destroy" the original textual provision. The problem with this argument is that the Court in Brushaber did not say that the Sixteenth Amendment cannot validly modify (or "destroy" if you will) the legal effect of the original text. Remember, this was Frank Brushaber's proposition, not the Court's proposition.
What the Court said was that Frank Brushaber's proposition and the Frank Brushaber contentions
were incorrect. The key language is the Court's verbiage "if acceded to." The key word is "IF." The point is that the Court did NOT accede to Mr. Frank Brushaber's contentions, or to his proposition. Frank Brushaber lost the case. That means that the Court did NOT rule that the Sixteenth Amendment could not modify (or could not "destroy") the legal effect of the original text.
The Court quoted the Amendment itself:
The Congress shall have power to lay and collect taxes on incomes, from whatever source derived, without apportionment among the several states, and without regard to any census or enumeration.
The Court then said:
It is clear on the face of this text that it does not purport to confer [a new] power to levy income taxes in a generic sense,-an authority [that was] already possessed [by Congress under the original text of the Constitution] and [that was] never questioned, - or to limit and distinguish between one kind of income taxes and another
In other words, the Sixteenth Amendment does not distinguish between one kind of income tax and another. And the original text of the Constitution already gave Congress the unquestioned power to tax incomes.
Instead, said the Court:
the whole purpose of the Amendment was to relieve all income taxes[,] when imposed[,] from [“the requirement of] apportionment [and to relieve all income taxes] from [the Pollock requirement that the courts engage in] a consideration of the source whence the income was derived . . . .
(bolding added).
Here, the Court clearly states that the purpose of the Amendment was to eliminate the need to consider the "source" of the income -- since (under the Amendment) NO income taxes are required to be apportioned.
"My greatest fear is that the audience will beat me to the punch line." -- David Mamet