When I started music school, I didn't know the difference between a Major 7 chord and a Dominant 7 chord; I could just read the chord pictures. So I thought I would add this note.

If you lower the 7th in your Major 7 chord, you have a Dominant 7 chord. If you lower the 3rd of your Dominant 7 chord, you have a minor 7 chord. If you lower the 5th of your minor 7 chord, you have a min7b5 chord. If you lower the 7th of your min7b5 chord, you have a diminished 7th.

Here are a couple of examples:



Cheers,
SarinaJ
http://www3.telus.net/public/wsalter/guitar/