The following is excerpted from "To Keep and Bear Arms," by Garry Wills, published September 21, 1995, in the New York Review of Books, pages 62-73, and is referenced by this discussion of the Second Amendment, here.
To keep. Gun advocates read "to keep and bear" disjunctively, and think the verbs refer to entirely separate activities. "Keep," for them, means "possess personally at home"--a lot to load into one word. To support this entirely fanciful construction, they have to neglect the vast literature on militias. It is precisely in that literature that to-keep-and-bear is a description of one connected process. To understand what "keep" means in a military context, we must recognize how the description of a local militia's function was always read in contrast to the role of a standing army. Armies, in the ideology of the time, should not be allowed to keep their equipment in readiness.
The constitutional ideology formulated in seventeenth-century England recognized that the realm's wealthy landowners and merchants were invited to share in the national government only or mainly when the king called parliaments into session, and he did that largely when he needed funds. One of the greatest urgencies for funds arose from war. If the king needed to raise and equip a new army for each war, he was dependent on the fresh revenues only a parliament could bring him in sufficient quantities. Thus it was to parliament's interest not to give any king the means to continue an army at his disposal. The more discontinuous his military efforts, the more was it necessary to call new parliaments, which could bargain for new powers of their own.
An army must be prevented from standing--from existing on a permanent basis. A pamphleteer against absolute monarchy wrote in 1675 that the king must not be allowed to "keep up a standing army." In 1697, the great ideologue of the militia movement, John Trenchard, warned against any situation where "a standing army must be kept up to prey upon our entrails." That applied not only to troops standing in readiness but to "stands" (stores) of arms.
To preclude, so far as possible, the maintenance of extraordinary forces by the king, local rulers (the squirearchy) kept in readiness a force--a militia--to handle all normal peacekeeping activity. Royal forces, except for those abroad in the navy or guarding Channel forts, were to be disbanded after each specific campaign, their arsenals broken up. Those who could not be reabsorbed into the normal economy should go to the militias, according to Trenchard. These latter were to maintain arsenals and all the equipment needed for "trained bands" (the normal term for individual militia bodies). In fact, at a time when more men were likely to have crossbows than "firelocks," Trenchard advised that "a competent number of them (firelocks) be kept in every parish for the young men to exercise with on holidays. These would be used on a rotating basis, since Trenchard proposed that only a third of the militia should be exercised at one time.
The idea of militia "stands" in common depots or arsenals was not confined to England. In America, the Articles of Confederation required that "every state shall always keep up a well regulated and disciplined militia, sufficiently armed and accoutered, and shall provide and constantly have ready for use, in public stores, a due number of field pieces and tents, and a proper quantity of arms, ammunition and equipage" (equipage being the etymological sense of arma. Thus it is as erroneous to suppose that "keep" means, of itself, "keep at home" as to think that "arms" means only guns. As Patrick Henry tells us, the militia's arms include "regimentals, etc."--the flags, ensigns, engineering tools, siege apparatus, and other "accoutrements" of war.
Some arms could be kept at home, of course. Some officers kept their most valuable piece of war equipment, a good cross-country horse, at home, where its upkeep was a daily matter of feeding and physical regimen. But military guns were not ideally kept at home. When militias were armed, it was, so far as possible, with guns of standard issue, interchangeable in parts, uniform in their shot, up keep, and performance--the kind of "firelocks" Trenchard wanted kept "in every parish" (not every home). The contrast with armies was not to be in performance (Trenchard and others boasted of the high degree of efficient organization in militias). The contrast was in continuity. The militia was always at the ready, its arms "kept." Armies came and went--their "continuation" was what Trenchard attacked.
Trenchard talked of militia arms being lodged in the proper hands--neither in an army's, on one side, nor in the lower orders, on the other (Trenchard's was a militia of property owners). In America, "deposition" of arms from the proper hands occurred, most famously, when the King's troops seized the militia's arsenals at Concord in the north and at Williamsburg in the south. That is where arms were kept, lodged, maintained.
To keep-and-bear-arms was the distinguishing note of the militia's permanent readiness, as opposed to the army's duty of taking up and laying down ("deponing" is Trenchard's word) their arms in specific wars. The militia was maintained on a continuing basis, its arsenal kept up, its readiness expressed in the complex process specified by "keep-and-bear." To separate one term from this context and treat it as specifying a different right (of home possession) is to impart into the language something foreign to each term in itself, to the conjunction of terms, and to the entire context of Madison's sentence.
 For the assumption that "keep" means "keep in the house" see Dowlut, "Federal and State Constitutional Guarantess to Arms," p. 69:"The bearing of arms in a public place is different from the keeping of arms in the house on account of the home's special zone of privacy." Private gun ownership is guaranteed, he claims, but the keeping of guns in the privacy zone. For keep as individual possession, see Robert E. Shalhope on "two distinct, yet related rights--the individual possession of arms and the need for a militia made up of ordinary citizens." "The Ideological Origins of the Second Amendment," Journal of American History (1982), pp. 599-614. Glenn R. Reynolds, one proponent of the Standard Model, quotes with approval the disjunction formulated by Donald B. Kates that "the term 'keep' refers to owning arms that kept in one's household; the term 'bear' refers to the bearing of arms while actually taking part in militia duties" (""A Critical Guide to the Second Amendment," p. 482).
 Anonymous pamphlet cited in Richard Ashcraft, Revolutionary Politics and Locke's 'Two Treatises of Government' (Princeton University Press, 1986), p. 118. Italics added.
 John Trenchard, An Argument, Shewing that a Standing Army Is Inconsistent with a Free Government and absolutely destructive to the Constitution of the ENglish Monarchy (London, 1697), p. 6. Italics added. A good brief description of the militia ideology is in Adam Smith, Lectures on Jurisprudence, pp. 268-269, 420-421. See Also J.G. A. Pocock, The Machiavellian Moment (Princeton University Press, 1975), Chapter 12, pp. 401-422, and Lois G. Schwoerer, 'No Standing Armies!': The Antiarmy Ideology in Seventeenth-Century England (Johns Hopkins University Press, 1974), pp. 174-187 (on Trenchard as "the great tutor" on militias). Hamilton says the objection to standing armies was to "keeping them up in a season of tranquility" (Federalist No. 25, p. 160). Italics in original.
 Trenchard, An Argument, p. 21
 Trenchard, An Argument, p. 21. Italics added.
 Trenchard, An Argument, p. 21
 "Articles of Confederation," in Jensen, editor, The Documentary History of the Ratification of the Constitution", Article VI, p. 88. Italics addded. As an English noun, "keep" meant the permanently holdable part of a castle (the equivalent of the Italian military term tenaza).
 Trenchard defends the "well-trained militia" agaisnt the arming of "an undisciplined mob" (An Argument, p. 20).
 A "continuation" of the army would make it an "establishment" (An Argument, p. 15).
 Trenchard, An Argument, pp. 7, 10.