On Science Blogs a commenter named Dingo Jack wrote the following wonderful comment.
Those poor Founding Fathers, they'd never have thought that even well-educated Americans wouldn't have a clue what a Nominative Absolute* is and how to use it.Dingo-----* The Nominative absolute is similar in structure and use to the Latin Ablative Absolute and the Greek Genitive Absolute (the subordinate clause being in the Nominative, Ablative and Genitive cases, respectively).
I'll translate for you: "[When a] ... well regulated Militia... [is] ... necessary... [for] ... the security of a free State, [then] the right of the people to keep and bear Arms shall not be infringed [but if the first clause is false, then the second clause is inactive.](The main clause is in bold, the subordinate clause in italics)
