Watch the A Dorian Mode online guitar lesson by Brad Carlton from Guitar Lab: Dorian Dominance
This lesson takes what you learned in your three note per string scale forms and adds one more note on each string. The resultant four note per string scale forms involve duplication. This means that the highest pitched note on each string will be repeated as the lowest pitched note on the next highest string. This is what I term breaking out of “tunnel vision” on the fingerboard. You will be required to stretch beyond what you're accustomed to but if you apply these forms to the higher register of the guitar, you won't feel as challenged. I will also demonstrate how to utilize these forms with legato slides and standard three finger fingerings.
As you study the A Dorian mode, you will notice patterns emerging with regard to adjacent notes in the scale. Be sure to memorize the intervallic pattern of this scale. All you need to remember is that the half steps occur between the 2 and b3 and also between the 6 and b7. All the other scale degrees are a whole step apart. This means that if you're viewing groups of four adjacent scale tones, they will fall into the following patterns: whole step half step whole step (1 2 b3 4 and 5 6 b7 1), half step whole step whole step (2 b3 4 5 and 6 b7 1 2), whole step whole step half step (4 5 6 b7, b7 1 2 b3), and whole step whole step whole step (b3 4 5 6).