[The] Congress shall have Power [...] To make all Laws which shall be necessary and proper for carrying into Execution the foregoing Powers, and all other Powers vested by this Constitution [in the Government of the United States, or in any Department or Officer thereof].To keep the Reed-Kellogg diagram size manageable we have removed the words in square brackets  that aren't essential to the analysis.
There appears to be no grammatical ambiguity in this clause as there is in the Tax/Spend/Welfare Clause previously diagrammed, so interpretation is mainly a matter of finding the original meanings of the words.
The key is the mandate that the laws authorized by this clause must be "necessary and proper". The conjunction "and" means they must satisfy both conditions, so in any case on whether such a power is legitimate, one would need to prove both "necessary" and "proper", not just one.
However, "necessary and proper" are further restricted by the prepositional phrase beginning with "for" that defines the purpose for which the laws must be "necessary and proper", specifically for "carrying into execution ... Powers", a gerund phrase. Therefore, anyone claiming a power under this clause must not only prove it is both "necessary" and "proper" but that it is also "for carrying into execution" a power otherwise delegated or "vested".
The implied power is only of a delegated or vested power found elsewhere in the Constitution, not of another implied power. This clause is not recursive. Only one level of implication from an explicit power is allowed.
What is "necessary"?
In the 1787 legal idiom "necessary" are not just about logical necessity, but practical necessity.
Consider a chain beginning with power A, for which power B is deemed necessary for carrying A into execution, for which power C is deemed necessary for carrying B into execution, and so forth. To make the discussion more concrete, let power A be the power to regulate some kind of interstate commerce, and power B the power to conduct official inspections of items of commerce at a border checkpoint. Strictly speaking, B is not logically necessary unless one inserts the additional premise, "Something may be regulated only if it is inspected by officials." But it is also possible to regulate by voluntary compliance without inspections, or perhaps by having competitors sue one another for noncompliance. So the necessity is practical rather than just logical.
Now in the next step we find a practical necessity, to carry into execution the power to conduct inspections, the power C to hire inspectors. That is a second level of inference. From that point we can move to a power D to pay inspectors, a power E to train inspectors, and a power F to supervise and discipline inspectors. However, all those steps in the chain are tethered to the original power A to regulate commerce.
The problem arises in that the tether may get broken as the chain grows. Persons may be hired to hire persons to hire persons to hire persons, none of whom actually conduct any inspections and thus carry into execution the power to regulate commerce. One can construct similar chains for things like acquiring land or equipment, initially for inspection stations but eventually for its own sake, or for imposing penalties, or for issuing forms, instructions, reports, etc.
If the practical inference were recursive, it would enable the growth of unlimited power, not tethered to the base power, contrary to original intent. Therefore, it is not recursive, and the phrase "for carrying into execution the foregoing powers ..." is a requirement that the "implied" power must always be practically necessary for carrying into execution the base power.
What is "proper"?
Some means were not considered proper, even if they might be practically necessary. We can identify some ways means may be improper:
- They violate a fundamental natural or social right, not just a negative right arising from the non-delegation of a power.
- They are not reasonable ways to attain the end.
- They do not serve a legitimate public purpose.
- They are not done in a way that satisfies due process or public deliberation.
- They exceed the bounds of public consent.
Thanks to Rob Natelson for finding a passage in a 1724 English book on legal forms in Latin:
... ad facienda exsequenda et expediendia omnia et singula et necessaria fuerint aut opportuna ... .with the abbreviations spelled out.
The words necessaria and opportuna are the neuter plural forms of necessarius (necessary) and opportunus (proper). In Latin, an important meaning of necessarius is a person connected to you. It can refer to a close relative, associate, and in particular to a dependent or servant. From that we get the strict notion of something being logically or practically necessary, but also subordinate.
The legal English of 1787 was largely derived from Latin and Law French, the languages of law until English was made the standard in English courts in the Proceedings in Courts of Justice Act 1730 (4 Geo II. c. 26). Although English had been allowed in courts since 1362, legal English continued to be dominated by the official use of Latin and Law French, to which one needs to refer to get the original meanings of many terms used in the Constitution.
What is "carrying into execution"?
The term of art "carrying into execution" had a fairly restrictive meaning in 1787. It did not extend to getting a desired outcome, such as compliance by the public with a law authorized by a delegated power. It meant only for an official to perform the duty of his office defined by a law, that is, to make a certain kind of effort. It was well understood and expected in 1787 that laws and enforcement efforts were unlikely to ever have full compliance, and might have very little compliance. That did not mean the official had whatever power he might need or find convenient to get such compliance. If he lacked enough power then he either had to have Congress amend the statute, if that was inadequate, within the Constitution, or amend the Constitution, with concurrence of 3/4 of the states.
So essentially, "carrying into execution" meant only administrative powers to acquire and use tools and resources for, and to remove obstacles to, performing duties. Extending powers under this clause to things that might "affect" commerce is a usurpation, because this clause only authorizes Congress to do things that enable the regulators in the performance of their duties. To extend powers any further would be to remove any limiting principle on the exercise of power under the Commerce Clause, and if "Commerce" is redefined to include all "economic activity", and not just trade in tangible commodities, then Congress would have unlimited power to do anything, which was obviously not intended or understood by the Framers. It would make the rest of the Constitution redundant.
To fix the precedent
To attempt to correct the erroneous line of precedents stemming from McCulloch v. Maryland (1819), the following clarifying amendment is proposed:
Article I Section 8 Clause 18 of this Constitution shall be construed to only include enablement of the completion of duties by duly elected or appointed officials, to make a limited, reasonable effort strictly necessary to exercise an express power narrowly construed, and not to go beyond completion of the duty to do whatever might be deemed convenient to get an outcome or result for which the effort might be made.The diagram
- What is the limiting principle? — Exploration of question raised by Justice Kennedy in oral arguments.
- Unnecessary and Improper — Analysis of Necessary and Proper Clause.
- The original meaning of "carrying into execution" — The restrictive phrase has never been properly adjudicated.
- Supreme Court decisions on Commerce and the Necessary and Proper Clause — Spreadsheet of cases showing the chain of deviation from original understanding.
- Clarifying Amendments — In the form of a bill.
- U.S. Constitution annotated — We will be adding links to diagrams from this copy.
- Commentaries on the Constitution of the United States, Book III Chapter 24, Joseph Story (1833) — Discusses the clause, but in a way that exhibits the infection from McCulloch v. Maryland.
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