I just recently started playing again after about a 20 year hiatus (yes that's right 20 years ) Anyway I've been studying the more technical aspects of chord theory and now I have a question that I used to know the answer to. A triad consists of a root, a major third (in the case of a major chord), and a perfect 5th. I think we can all agree on that. Of the major chords A, C, D, E, and G all seem to work out fine but the G major chord is a little strange in that the fingered notes being played are G, B and then another G on the 1st string. Is it true that the open D string serves as the perfect fifth to complement this major chord? Is it true that all open strings always count toward the notes in the chord? Because I seem to remember that sometimes they were just played for depth. I realize this question might be quite dumb so brutal answers are fine.
yes, open strings count as part of the chord. The open D is the fifth, with the open G and B being the root and thirds. The B string can also be fingered on the 3rd fret to give D which will give you two fifths instead of two thirds. Every note played is counted in the chord in some way.