What principle lies behind the 9th amendment, which states that the Bill of Rights is not a complete list of citizens' rights?

The principle behind the 9th amendment is that the enumeration of certain rights in the Bill of Rights does not mean that other rights of the people should be disregarded or denied. In simpler terms, it asserts that the rights of citizens are not restricted solely to those explicitly mentioned in the Constitution.

The 9th amendment reads:
"The enumeration in the Constitution, of certain rights, shall not be construed to deny or disparage others retained by the people."

The purpose of this amendment is to ensure that the government does not use the Bill of Rights as a means to narrow down or undermine the rights of the people as listed in the Constitution. It recognizes that the Constitution implicitly protects a broad range of rights beyond those explicitly stated, and those rights should not be ignored or violated by the government.

This allows for the interpretation and expansion of rights over time, recognizing that societal values and needs may evolve and new rights may emerge that were not originally specified in the Constitution. The 9th amendment serves as a safeguard against a narrow interpretation of rights by reminding us that the list in the Bill of Rights is not exhaustive and that all other rights not specifically mentioned are still retained by the people.