Final answer:
The most common method for adding an amendment to the Constitution is through a proposal by two-thirds of both chambers of Congress. This method has been used in all 27 ratified amendments, including the Bill of Rights. On the other hand, the method that has only been used once is the petitioning of Congress by two-thirds of the state legislatures to call a national convention.
Step-by-step explanation:
Amending the Constitution is a significant act that requires a change to the document that guides our national governance. The amendment process is a two-step process. First, to propose an amendment, two-thirds of both chambers of Congress must agree to the proposal, or two-thirds of the states may call a convention. Second, to ratify an amendment, three-fourths of the state legislatures must agree to adopt it.
Historically, the most common method for adding an amendment to the Constitution has been through the first step, where two-thirds of both chambers of Congress propose the amendment. This method has been used in all 27 ratified amendments, including the first ten amendments known as the Bill of Rights.
On the other hand, the method that has only been used once is the second step, where two-thirds of the state legislatures petition Congress to call a national convention to propose amendments. However, to date, this method has never been used apart from its initial use in convening the Constitutional Convention to draft the original Constitution.