Caitrin, the militia is obviously made up individual militiamen, who are the people mentioned in the amendment's second phrase. In the definition Midchuck shared with us about 10 posts up, you can see that the militia in question is an unorganized body, not an organized one. It still DOES NOT say that you ONLY get to bear arms on the CONDITION that you're in some militia. It says you get to bear them BECAUSE we NEED a militia, said militia being essentially every citizen, if and when needed.

To paraphrase it in modern language: Since having every citizen ready to put up a good fight is necessary to protect our country's security and freedom, the right...

Note how compactly the original language states the above. Good writing. Unfortunately, "well regulated" gets misinterpreted as meaning "carefully controlled and organized", and "militia" gets misinterpreted as "National Guard". When one considers the amendment in the context of the political climate and language usage of the time when it was written, it becomes a l-o-n-g stretch, and an ungrammatical one, to read it as meaning "Only within an organized militia..."