Why mustn't the negatives be cancelled in: 'enumeration … does not presuppose something not enumerated'?

Question

Source: United States v. Lopez, 1995, US Supreme Court, majority opinion by Rehnquist

To uphold the Government's contentions here, we have to pile inference upon inference in a manner that would bid fair to convert congressional authority under the Commerce Clause to a general police power of the sort retained by the States. Admittedly, some of our prior cases have taken long steps down that road, giving great deference to congressional action. The broad language in these opinions has suggested the possibility of additional expansion, but we decline here to proceed any further. [1.] To do so would require us to conclude that the Constitution's enumeration of powers does not presuppose something not enumerated, and that there never will be a distinction between what is truly national and what is truly local. This we are unwilling to do.

1. This superlative answer and its use of logic especially helped me, but doesn't duplicate this; I still wouldn't know how to parse the bold text until after determining that the negatives in the bold text mustn't be cancelled. Why not though? How can you discover or foreknow so?

2. This question reaffirms my categorical misunderstanding of StoneyB's answer and my gnawing plight with negatives. So how can I learn about and delve into 'cancellations', 'predications', 'scopes'?

Answer 1

It's true, a "double negative" is not proper English.

I never didn't see him.

However, to be considered a double negative, the negating words (no, never, not) must modify the same word. Here, never and not modify see.

I never saw him not take anything from there.

Since it's fairly common knowledge that English prohibits double negatives, mutliple use of them may tend to sound at least a bit awkward and can confuse a listener/reader off guard. But the above is OK. Never modifies saw, and not modifies take.

Similarly:

Enumeration of powers does not presuppose something not enumerated,

Not modifies presuppose and the second not modifies enumerated. This is OK.

Answer 2

To do so would require us to conclude that the Constitution's enumeration of powers does not presuppose something not enumerated...

The core idea here is that the enumeration of congressional powers contains only the powers that the framers of the Constitution saw fit to grant, and no others, because a list, by its very nature, intentionally contains only the items that it contains; implicit in the idea of a list is that there are items that are not in the list.

To get to this idea, let's do subject, verb, object analysis of the object complement clause of "require us to conclude". Require us to conclude what?

SUBJECT the Constitutions's enumeration = this list of congressional powers we're discussing

VERB does not presuppose = does not require as an antecedent fact or premise

OBJECT Something not enumerated = something not in that list (in the enumeration of powers)

As the object of the verb phrase, "something not enumerated" must be left intact. Don't toggle its "not". It refers to any unenumerated power (i.e. not in the list).

Let's put the OBJECT COMPLEMENT CLAUSE back together:

... this list of congressional powers we're discussing does not require as antecedent fact or premise some power not in that list

That is what Rehnquist refuses to conclude.

In other words, why make an enumeration in the first place if there are not items that are to be excluded from the list? One could simply say "all" and have done with it. An enumeration by its very nature implies that it is including some things and excluding others. Justice Rehnquist refuses to expand Congressional powers because to do so would require that he give up this basic tenet about the nature of enumerations in general.