When James Madison introduced his resolutions for the bill of rights to the House, including what would become the Ninth Amendment, he said:
It has been objected also against a bill of rights, that, by enumerating particular exceptions to the grant of power, it would disparage those rights which were not placed in that enumeration; and it might follow by implication, that those rights which were not singled out, were intended to be assigned into the hands of the General Government, and were consequently insecure. This is one of the most plausible arguments I have ever heard against the admission of a bill of rights into this system; but, I conceive, that it may be guarded against.
Madison was, in other words, guarding against the well-understood rule of inclusio unius est exclusio alterius, whereby the very listing of certain rights as immune from congressional regulation would necessarily imply a grant of general legislative power in Congress to legislate over all others.