Virginia, Pennsylvania, Kentucky, and Massachusetts share an interesting trait: They're the only four states in the U.S. that have the word commonwealth as part of their official title. The name may sound fancy, but commonwealths are no different from the 46 "regular" states that comprise the nation.
According to Merriam-Webster, commonwealth describes a nation, state, or other political unit "founded on law and united by compact or tacit agreement of the people for the common good." In other words, the term isn't specific to any type of centralized political organization. Rather, it can be applied to any body invested in the "common wealth" (a.k.a. well-being) of the population it governs.
Whether or not a state was deemed a commonwealth depended on the views of its founders. The Massachusetts State Government website explains that the word commonwealth became popular during the American Revolution. When drafting Massachusetts's constitution, John Adams prized the term for its anti-monarchy and pro-democracy connotations.
"There is, however, a peculiar sense in which the words republic, commonwealth, popular state, are used by English and French writers; who mean by them by them a democracy [...] a single assembly, chosen at stated periods by the people," the Founding Father wrote.
His preference for commonwealth over state didn't have any greater consequences beyond semantics. The commonwealths of Virginia, Pennsylvania, Kentucky, and Massachusetts still function as states on a political and legal level. On the flip side, the U.S. territories Puerto Rico and the Northern Mariana Island are commonwealths by name, but they don't have the same rights as the states that share the title.
So in conclusion: Knowing which U.S. states are technically commonwealths is a fun piece of trivia to know for road trips, but the distinction doesn't have any impact on the people who live there.
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