I can’t answer your question, but am providing some additional information.
The quoted text comes from Section 63 (e) of the Internal Revenue Code, and the context is as follows:
Title 26 – Internal Revenue Code
Subtitle A – Income Taxes
Chapter 1 – Normal taxes and surtaxes
Subchapter B – Computation of Taxable Income
Part I – Definition of Gross Income, Adjusted Gross Income, Taxable Income, etc.
Section 63 – Taxable Income Defined
Subsection (e) Election to itemize
Chapter 2a – Unearned Income Medicare Contribution – i.e. Net Investment Income Tax
Thus, the translation of the quoted text is:
Unless an individual makes an election under [Subsection (e) – Election to Itemize], no itemized deduction shall be allowed for the taxable year. For purposes of [Subtitle A – Income Taxes], the determination of whether a deduction is allowable under [Chapter 1 – Normal taxes and surtaxes] shall be made without regard to the preceding sentence.
This does seem to be nonsensical in that it is saying that the first sentence, which is part of Chapter 1, does not apply to any tax covered by Chapter 1.
And what about the Net Investment Income Tax (Chapter 2a) ?
Here’s the link: