Let's go. The first 7th chord most of us learn is called just that: C7, G7, A7, etc. It seems reasonable to assume these consist of the root, 3rd, 5th and 7th of the scale, right? Wrong!
All the chords built on other notes in the scale of C are minor ... of a V chord can be shown by the symbol V7. For example, G7 is made by taking the major triad of G (G - B - D) and adding ...