Section 8 gives the Congress the power to tax for several purposes. It starts out with the power to tax, and a preamble, listing a summary of the purposes behind taxation. Specifically, it says Congress can pay government debts, provide for the common defense, and provide for the general welfare:
8.1 The Congress shall have Power to lay and collect Taxes, Duties, Imposts and Excises, to pay the Debts and provide for the common Defense and general Welfare of the United States; but all Duties, Imposts and Excises shall be uniform throughout the United States;
These three summarized powers are then defined in detail below. As you read, note that some powers clearly relate to the common defense, others to paying debts, and the rest to what the Constitution means by ‘provide for the general welfare’. The ‘powers’ listed in 8.1 are not enumerated powers in 8.1, but only as defined below.
8.2 To borrow Money on the credit of the United States;
8.3 To regulate Commerce with foreign Nations, and among the several States, and with the Indian Tribes;
8.4 To establish a uniform Rule of Naturalization, and uniform Laws on the subject of Bankruptcies throughout the United States;
8.5 To coin Money, regulate the Value thereof, and of foreign Coin, and fix the Standard of Weights and Measures;
8.6 To provide for the Punishment of counterfeiting the Securities and current Coin of the United States;
8.7 To establish Post Offices and post Roads;
8.8 To promote the Progress of Science and useful Arts, by securing for limited Times to Authors and Inventors the exclusive Right to their respective Writings and Discoveries;
8.9 To constitute Tribunals inferior to the Supreme Court;
8.10 To define and punish Piracies and Felonies committed on the high Seas, and Offenses against the Law of Nations;
8.11 To declare War, grant Letters of Marque and Reprisal, and make Rules concerning Captures on Land and Water;
8.12 To raise and support Armies, but no Appropriation of Money to that Use shall be for a longer Term than two Years;
8.13 To provide and maintain a Navy;
8.14 To make Rules for the Government and Regulation of the land and naval Forces;
8.15 To provide for calling forth the Militia to execute the Laws of the Union, suppress Insurrections and repel Invasions;
8.16 To provide for organizing, arming, and disciplining, the Militia, and for governing such Part of them as may be employed in the Service of the United States, reserving to the States respectively, the Appointment of the Officers, and the Authority of training the Militia according to the discipline prescribed by Congress;
8.17 To exercise exclusive Legislation in all Cases whatsoever, over such District (not exceeding ten Miles square) as may, by Cession of particular States, and the Acceptance of Congress, become the Seat of the Government of the United States, and to exercise like Authority over all Places purchased by the Consent of the Legislature of the State in which the Same shall be, for the Erection of Forts, Magazines, Arsenals, dockyards, and other needful Buildings;–And
8.18 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.
Just to be even more clear that this list – 8.2 to 8.18 – is the ENTIRE list of federal legislative power, the founders then wrote the 10th Amendment:
The powers not delegated to the United States by the Constitution, nor prohibited by it to the States, are reserved to the States respectively, or to the people.
Note that the Constitution does NOT say that government cannot legislate to do more than listed in Article 1, 8.2-8.18. It merely says that the FEDERAL government cannot do more than that.
If California wants socialized medicine, as long as it can provide it without violating the Bill of Rights, or its own Constitution, as a sovereign state, it has that authority. If Massachusetts wants to enact Romneycare, as a sovereign state, it has that authority. If Washington wants to enact a minimum wage, as a sovereign state, it has that authority.
None of those things are constitutional powers of the federal government, and in fact about 80% of what the federal government does today is blatantly unconstitutional.