The decision to amend the Constitution with a Bill of Rights was opposed by many Americans in 1787-1791. This was not because they opposed citizens' being guaranteed specific, enumerated rights, but because they feared that later presidents, congresses and judges might say the list was exclusive. So the Ninth and Tenth amendments were added.
The Ninth Amendment says, "The enumeration in the Constitution of certain rights shall not be construed to deny or disparage others retained by the people." The Tenth Amendment says, "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 the people."
One legal scholar has written that these two amendments really just say of the eight that precede them, "We mean it!"
A generation after the Framers, the Tenth Amendment became the "states' rights amendment." Opponents of a strong federal government and of federal supremacy successfully invoked it often in the 19th century, not only before the Civil War but after it. As late as the 1930s the Supreme Court was denying Congress' right to enact laws some states opposed.
That changed, and the Tenth Amendment appeared to be dead -- until the 1970s, when Supreme Court decisions started citing it, and references to "federalism" appeared more often. Some conservatives expect the present court to continue to breathe life back into the Tenth Amendment until it is as robust as it once was.
Some liberals hope someone will breathe life back into the Ninth Amendment. That is because it may be the only way to rescue the right to privacy in general and the right to abortion in particular.
No Supreme Court decision has ever relied on the Ninth Amendment. But in the 1965 case that prepared the way for Roe vs. Wade, Justice Arthur Goldberg, a liberal Democrat, wrote a concurring opinion saying that "fundamental personal rights" nowhere mentioned in the Constitution or the Bill of Rights exist, derived from "the traditions, conscience and experiences and principles which lie at the base of our civil and political institutions."