The Second Amendment, part of the Bill of Rights added to the original Constitution in 1791, states: "A well regulated Militia being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed." In other words: since a militia, provided that it is well regulated, is a very good thing for a free state to have, the federal government must not be allowed to castrate it by forbidding the people of the United States to possess weapons. For then the militia would have no weapons, and an unarmed militia is an oxymoron.
Politically conscious Americans in the late eighteenth century feared standing armies, having fought the British army in the Revolution, and feared centralized government (as in Britain); and on both counts they wanted to make sure that the states would be allowed to have armed militias. The federal government could regulate them but not disarm them. The fear was that in the absence of such a provision in the Bill of Rights, the provision in Article I of the Constitution authorizing Congress to organize, arm, discipline, and call into service "the Militia" (a term that embraces the state militias, because the same provision reserves the right to train and officer "the Militia" to the respective states) would enable Congress to disarm them. That fear surfaced in the debates over the ratification of the original Constitution and was, as Justice John Paul Stevens's dissenting opinion explains, the motivation for the Second Amendment.
The text of the amendment, whether viewed alone or in light of the concerns that actuated its adoption, creates no right to the private possession of guns for hunting or other sport, or for the defense of person or property. It is doubtful that the amendment could even be thought to require that members of state militias be allowed to keep weapons in their homes, since that would reduce the militias' effectiveness. Suppose part of a state's militia was engaged in combat and needed additional weaponry. Would the militia's commander have to collect the weapons from the homes of militiamen who had not been mobilized, as opposed to obtaining them from a storage facility? Since the purpose of the Second Amendment, judging from its language and background, was to assure the effectiveness of state militias, an interpretation that undermined their effectiveness by preventing states from making efficient arrangements for the storage and distribution of military weapons would not make sense.
Note first that Posner's version of originalism focuses on the supposed "motivation" for the Second Amendment. Posner is using "original intent" originalism, not "original meaning" originalism. While looking at probable intent can be revealing, it can also deteriorate into what Randy Barnett has called "channeling the framers."
Second, Posner cites no early authority for his view of original intent (or original meaning) other than the text itself and Justice Stevens's opinion.
As for Posner's textual analysis, we know from Eugene Volokh's pathbreaking analysis of preambles in early state constitutions that preambles were not viewed as significantly limiting the underlying rights they granted. Even if Posner were correct that protecting state militias was the only goal of the Amendment -- and there is evidence against this proposition and no evidence in favor of it -- the framers may still have chosen to guarantee a right broader than was necessary to fulfill that motivation. That's one reason it's important to look primarily at the language they chose, not mostly at their motivations for acting.
But the bigger problem has already been suggested: how does Posner know that the framers did not have broader goals for the Amendment? There is no evidence that they intended the Second Amendment to be limited to militia and some evidence that they didn't. Indeed, several contemporary authorities that addressed whether the proposed or recently adopted amendment protected an individual right described it as doing so.
Posner states categorically what the originalist interpretation of the text is or should be, but if he is correct, why did no framer or early commentator ever offer that view? Why did several early commentators treat the Second Amendment (or its drafts) as guaranteeing an individual right, including in some cases a right for the purposes of self-defense and hunting?
As for Posner's hypothetical about seizing weapons in wartime, I don't see how it significantly advances his argument. Rights are not absolute. First, if there is a right, then the state should be loathe to seize weapons except in the direst of emergencies. Second, if the state did take weapons, the state would have to pay for this taking, as it would if it took any other property covered by property rights protected by the state. (Also, I recall that some states (and/or colonies) treated firearms as privileged, protecting them from distress for debts.)
On evidence from the first major commentator on the Second Amendment, St. George Tucker, here is the leading young historian on the legal and political history of guns in the late colonial early republic periods, Robert Churchill:
It is clear from the Tucker's gloss on the Second Amendment in the manuscript draft [from the early 1790s] that he saw in the amendment a guarantee that extended well beyond the concern over federalism that Cornell discusses. Tucker noted that "in England the people have been disarmed under the specious precept of preserving the game." In a note on the facing page, Tucker commented that in England, "the right of the people to bear arms" was by the inclusion of limiting language "entirely done away." In this gloss, Tucker suggested that the passage of England's game laws had in England eliminated the constitutional protection that the Second Amendment was intended to guarantee. Tucker reiterated this view in 1803, noting that under the game laws in England, "the right of keeping arms is effectually taken away," while expressing his hope that in America, "the people will never cease to regard the right of keeping and bearing arms as the surest pledge of their liberty."
The problem for Saul Cornell's argument is that England's game laws prohibited citizens, the vast majority not enrolled in the militia, from possessing firearms for private purposes. That Tucker saw the game laws as a contravention of the right protected by the Second Amendment is clear evidence that he understood that right to apply in America to all citizens and to weapons owned for both public and private purposes. Tucker's view mirrors that of Samuel Nasson and Saumel Latham Mitchel, cited by Cornell, and of a supporter of Samuel Adams in August 1789 who interpreted the House draft of the Second Amendment as a vindication of Adams's earlier proposed amendment that prohibited Congress from preventing "the people of the United States, who are peaceable citizens, from keeping their own arms." All of these early interpreters of the language embedded in the Second Amendment understood it to guarantee a right to keep arms that transcended "the inextricable connection" to militia service that Cornell posits.
If the view of the 2d Amendment advanced by Judge Posner, Justice Stevens, and Prof. Cornell were the original view of the framers, why didn't any of the framers or early commentators ever say so? And why was this new "civic rights" advanced by Stevens and Cornell rarely mentioned by anyone until about a decade ago?
After discussing originalism, Posner then writes about changed circumstances, an argument on which he is on much firmer ground.
BTW, Dick Posner and I are co-teaching a course in judicial behavior this coming school year (along with Bill Landes and Lee Epstein). Thus, I hope to explore his views on originalism in more detail in the next few months.