Watch the Modal Study #4 online guitar lesson by TrueFire from Rock Guitar Greatest Hits Vol. 1
Lesson Source: Jon Finn's Modal Rock Soloing
C dorian is a Bb major scale starting on its 2nd degree. C dorian is also a C major scale with b3 (Eb) and b7 (Bb). Another way to think of it is that C dorian is a C mixolydian scale with a b3. Further, C dorian is a C minor pentatonic scale (1, b3, 4, 5, b7 or C, Eb, F, G, Bb) with 2 (D) and 6 (A) added. You'll find that the characteristic note is the 6th (A). Note that all the pentatonic notes will sound sweet. The 6th (A) will sometimes sound perfect and other times odd. It's called the characterisitic note because dorian is the only minor sounding mode with 6ths. The others, Aeolian and Phrygian have b6.