Originally posted by u10ajf
It's worth mentioning that if you extend a chord far enough your expression will include all the notes of a given scale, so a 13th chord expresses all 7 notes of a particular scale.

Although on the guitar it's impossible to play all 7 notes on a 6 stringer. Usually one or more notes will be excluded, just as long as the 3rd, 7th, and 13th are there. Another thing is when a 13th chord is heard; the minor 13th matches with the (root) minor scale, the major 13th matches with the (root) major scale, and the dominant 13th matches with the mixolydian mode. You won't hear a truly natural 13th chord on any other chordal tone. If so it's most likely a dominant 13th in a cycle 5th. Keyboardists tend to use them alot.