Specifically, Thalberg argued that justification is not transmissible through valid deduction.

Essentially, the two provisions have the effect of disallowing otherwise valid deductions from taxable income, thereby giving the taxpayer a disguised higher marginal rate.

We have valid deductions that the I.R.S. has certified.

While never a valid deduction, if such an inference can be made on statistical grounds, it may nonetheless be convincing.

This is the key feature of a logically valid deduction.

If the premises of a logically valid deduction are true, then the conclusion must be true.

This is a perfectly valid deduction.

But this does not affect the status of the argument as a valid deduction.

That is, the argument is a logically valid deduction.

Given the truth of the assumptions, a valid deduction guarantees the truth of the conclusion.