Final answer:
The 9th Amendment does not address federal income tax. It was the 16th Amendment that cleared doubts about the constitutionality of a federal income tax by explicitly allowing Congress to tax individual incomes without apportionment among the states.
Step-by-step explanation:
No, the 9th Amendment to the U.S. Constitution did not remove all doubt that a federal income tax was allowed under the U.S. Constitution. In fact, it was the 16th Amendment that explicitly granted Congress the power to lay and collect taxes on incomes, without apportionment among the states and without regard to any census or enumeration. The 9th Amendment simply ensures that the enumeration in the Constitution, of certain rights, shall not be construed to deny or disparage others retained by the people, which sets out a principle of legal interpretation but does not address taxation directly.
After the Populists of the 1890s sought the enactment of a federal income tax, and previous attempts to tax the wealthy through direct taxes were found to be unconstitutional, the 16th Amendment was proposed and ratified. It resolved the issue by authorizing the national government to directly tax the incomes of individuals. This was significant because every year, people pay taxes on the money that they make from a job or trade, and prior to the 16th Amendment, there was legal ambiguity about the federal government's ability to enforce an income tax. The ratification of the 16th Amendment in 1913 clarified this power, enabling Congress to impose a federal income tax which has evolved over time and affects a large portion of Americans today.