As with all of the Constitution, the meaning of the Second Amendment must be gleaned from its own words and phrases. These should first be examined as a whole, then considered separately.
In its entirety, the Second Amendment consists of two clauses: an introductory subordinate or modifying clause—“[a] well regulated Militia, being necessary to the Security of a free State”, followed by an independent or main clause—“the right of the people to keep and bear Arms, shall not be infringed”.
Grammatically, “[a] well regulated Militia, being necessary to the security of a free State” is denoted a “nominative absolute clause”. Even contemporary American high-school students—as poorly educated as too often they are—should understand what an “absolute clause” is and does: (footnote 2) An “absolute clause” modifies the whole of the sentence in which it is contained, adding important information, sometimes (as in the case of the Second Amendment) the most important information in the sentence. An “absolute clause” identifies relationships between ideas expressed within the sentence—quite often, the reason for or the cause of what is expressed in the main clause.
In the late 1700s, no one fluent in the English language, let alone literate in pre-constitutional American law, would have read the Second Amendment with any other rule of grammatical construction in mind:
Anyone studying * * * English grammar in the eighteenth century would have understood how an absolute phrase works. And since the absolute phrase already had become a normal, naturalized English construction by then, any competent English writer at the time would have been able to use the absolute construction without having taken any formal grammar lessons.
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Most American readers in the federal period, including those without formal grammar study, would have had no trouble understanding that the Second Amendment’s absolute construction functioned to make the Amendment effectively read: because a well regulated Militia is necessary to the security of a free State, the right of the people to keep and bear Arms shall not be infringed. (footnote 3)
This grammatical analysis is controlling, because the rule employed for construing statutes in the late 1700s required that if “the reason of the law” is “expressed in such clear and precise words, as to leave no doubt at all about the ultimate effect which the lawmaker designed to produce, or about the end which he designed to obtain”, then “the meaning of the law is to be determined by the reason of it”. (footnote 4) “If, from the imperfection of human language, there should be serious doubts respecting the extent of any given power, * * * the objects for which it was given, especially when those objects are expressed in the instrument itself, should have great influence in the construction.” (footnote 5) Which in the case of the Second Amendment means that the pith (if not the entire substance) of “the right of the people to keep and bear Arms” must be ascertained by reference to the preceding clause. For, plainly enough, “the reason”, “effect”, “end”, and “objects” of the Amendment are “expressed in * * * clear and precise words” in the Amendment itself, with an emphasis to be found nowhere else in the Constitution: “[a] well regulated Militia, being necessary to the security of a free State”.
And because (as just noted), “‘[i]n expounding the Constitution * * * , every word must have its due force, and appropriate meaning; for it is evident from the whole instrument, that no word was unnecessarily used, or needlessly added’”, (footnote 6) therefore, whatever else the “right of the people” might entail, it must to a decisive degree always conduce to, operate within, and advance “[a] well regulated Militia”, so that “[a] well regulated Militia” can conduce to, operate within, and advance “the security of a free State”. Reciprocally, “a free State” must be one with “[a] well regulated Militia”. And “[a] well regulated Militia” must be one in which “the people” participate through the untrammeled exercise of their “right * * * to keep and bear Arms”. “[T]he right of the people to keep and bear Arms” is not merely incidental to “[a] well regulated Militia” and vice versa; instead, each is integral to and inextricable from the other. So, “the right of the people to keep and bear Arms” cannot be interpreted without reference to “[a] well regulated Militia”; and “[a] well regulated Militia” cannot be understood without reference to “the right of the people to keep and bear Arms”. (footnote 7)