When the Constitution was ratified, the Framers unanimously believed that the "militia" included all of the people capable of bearing arms.
George Mason, one of the Virginians who refused to sign the Constitution because it lacked a Bill of Rights, said: "Who are the Militia? They consist now of the whole people." Likewise, the Federal Farmer, one of the most important Anti-Federalist opponents of the Constitution, referred to a "militia, when properly formed, [as] in fact the people themselves."
In 1789, the rule of construction was that, the words of a legal instrument should
be generally understood according to their usual and most known significations. (See Blackstone's
Commentaries of the Laws of England) In 1789, The most known significations of the word 'militia" were "the standing force of a nation" and "train-bands." (See 1787 edition of
A Dictionary of the English Language)
The "subject matter" defined the term " well regulated militia" as " the body of the people", "trained to arms" (trained in war) [for the "safe defense of a free state", "under strict subordination to, and governed by, the civil power"] (See the 1776 Virginia Bill of Rights)
That a well regulated militia, composed of the body of the people, trained to arms, is the proper, natural, and safe defence of a free state; that standing armies, in time of peace, should be avoided, as dangerous to liberty; and that, in all cases, the military should be under strict subordination to, and governed by, the civil power.
--Virginia Bill of Rights 1776
George Mason, one of the Virginians who refused to sign the Constitution because it lacked a Bill of Rights, said: "Who are the Militia? They consist now of the whole people."
What militia was Mason talking about?
The Original Pre-Amendment Constitution doesn't say the militia is the whole people. All it tells us about the militia is that Congress has the power to organize, arm, discipline and govern it, and that the States have power to appoint officers and train the militia according to the discipline prescribed by Congress.
Thus, we conclude, theword "militia" in the Constitution means
a body of individuals organized (as a military force),
armed (with weapons of war),
disciplined (instructed in military matters and governed by military rules and regulations),
trained (to be a military force) and commanded by
officers.