Article I, Section 1

But the institution can't just make any old law it wants to. Enumerating, or listing, congressional powers is meant to make it clear what Congress should be allowed to do. The enumerated powers are quickly followed by a list of things that Congress is expressly forbidden from doing. Some of the founders wanted it both ways: empower the legislature to do stuff it couldn't do under the Articles but also keep Congress leashed so that it can't make laws that don't fit with the Constitution. Hmmm... I wonder if the balance was struck properly...