I'am a new memeber to this site. I started studying theory about 5-6 months ago and love it. I own all of your books, Beginning - Mastering, those books tought me alot of what I know and are an excellent tool. Having said that, I have a few questions. My question is about chord extensions. I have multiple books that talk about chord extensions and describe them as: You stack additional thirds to get chord extensions 9, 11, and 13. My question is, extensions 9, 11, and 13 are, as you know, scale degrees 2, 4, 6 transposed an octave higher. I found out something that contradicts the process of adding a third on top of a seventh chord. When I stack a third on a seventh (C maj 7) I get the note D# (8th fret on the G string) which is a half-step above D ( in the key of C major), the second scale degree. I found out that the distance from the seventh of the Cmaj 7 chord to the 9th is a flat third. The seventh is a F#. The second scale degree, transposed up an octave, is a D natural. I have noticed this in several other books as well, that these extensions are a third away. I'am I missing something? Why does this occur? Am I wrong?