In the latter half of the 20th century, there was considerable debate over whether the Second Amendment protected an individual right or a collective right.[145] The debate centered on whether the prefatory clause ("A well regulated militia being necessary to the security of a free State") declared the amendment’s only purpose or merely announced a purpose to introduce the operative clause ("the right of the People to keep and bear arms shall not be infringed"). Scholars advanced three competing theoretical models for how the prefatory clause should be interpreted.[146]
The first, known as the "states' rights" or "collective right" model, held that the Second Amendment does not apply to individuals; rather, it recognizes the right of each state to arm its militia. Under this approach, citizens "have no right to keep or bear arms, but the states have a collective right to have the National Guard".[126] Advocates of collective rights models argued that the Second Amendment was written to prevent the federal government from disarming state militias, rather than to secure an individual right to possess firearms.[147]
Prior to 2001, every circuit court decision that interpreted the Second Amendment endorsed the "collective right" model.[148][149]
However, beginning with the Fifth Circuit's opinion United States v. Emerson in 2001, some circuit courts recognized that the Second Amendment protects an individual right to bear arms.[150]
The second, known as the "sophisticated collective right model", held that the Second Amendment recognizes some limited individual right. However, this individual right could only be exercised by actively participating members of a functioning, organized state militia.[151][152] Some scholars have argued that the "sophisticated collective rights model" is, in fact, the functional equivalent of the "collective rights model."[153] Other commentators have observed that prior to Emerson, five circuit courts specifically endorsed the "sophisticated collective right model".[154]
The third, known as the "standard model", held that the Second Amendment recognized the personal right of individuals to keep and bear arms.[126] Supporters of this model argued that "although the first clause may describe a general purpose for the amendment, the second clause is controlling and therefore the amendment confers an individual right 'of the people' to keep and bear arms".[155] Additionally, scholars who favored this model argued the "absence of founding-era militias mentioned in the Amendment's preamble does not render it a 'dead letter' because the preamble is a 'philosophical declaration' safeguarding militias and is but one of multiple 'civic purposes' for which the Amendment was enacted".[156]
Under both of the collective right models, the opening phrase was considered essential as a pre-condition for the main clause.[157] These interpretations held that this was a grammar structure that was common during that era[158] and that this grammar dictated that the Second Amendment protected a collective right to firearms to the extent necessary for militia duty.[159] However, under the standard model, the opening phrase was believed to be prefatory or amplifying to the operative clause. The opening phrase was meant as a non-exclusive example—one of many reasons for the amendment.[45] This interpretation is consistent with the position that the Second Amendment protects a modified individual right.[160]
The question of a collective right versus an individual right was progressively resolved in favor of the individual rights model, beginning with the Fifth Circuit ruling in United States v. Emerson (2001), along with the Supreme Court's rulings in District of Columbia v. Heller (2008), and McDonald v. Chicago (2010). In Heller, the Supreme Court resolved any remaining circuit splits by ruling that the Second Amendment protects an individual right.[161] Although the Second Amendment is the only Constitutional amendment with a prefatory clause, such linguistic constructions were widely used elsewhere in the late eighteenth century.[162]