I have been learning to play the "Blues" for over a year.
I have learned several of the pentatonic boxes in several keys.
Now I am learning "Blue Chords" to go with my leads.
My instructor has taught me the 9th chords.

Example: G7-C9-D9. What is nice about using the 9th chords, is
they all can be played within 3-frets, which I can do without looking down
at the neck.

Most of my Blues Guitar Chord books show all 7th-chords (G7-C7-D7),
which requires moving up & down to multiple fret, which would require me to look at the neck.

My question is: when do you use 7th-chords and when do you use 9th-chords? :confused: