One big revelation for me was realizing that all the modes are one big pattern, you just move the root. Think of a keyboard, if you play white keys from C to C its a major scale, D to D is Dorian, G to G is MIxolydian etc. The same applies to the guitar or bass, any instrument. If you know the standard major scale pattern and you play it from the second note going up and add a note a whole step up its now a Dorian mode.
Learn the modal boxes, Major, Dorian, natural minor, all of em.
Once you get comfortable with these patterns you can play any mode in any key anywhere on the neck. Understanding diatonic harmony is important too. Diatonic just means all the notes of the harmony come from one scale, not all music is like that but a lot is and it's a good place to start.
check this out:
1 - 2 -3 - 4 - 5 - 6 -7 - 8
C - D - E- F - G - A - B - C -
1 - 1 - 1/2 - 1 - 1 - 1- 1/2
that is the step pattern for the major scale and it's the key to the universe.
1 = whole step or 2 frets and 1/2 is half step, one fret.
On the keyboard the half steps are the white keys without blacks in between em, the black keys are the sharps/flats. Sorry if this rehash for ya.
I should pause here to say learning your intervals, the distance between notes is a big deal to. Whole steps, half steps, octaves, fifths etc. these are represented bu the numbers above the scale. C to G is a fifth etc. We would also refer to G as the fifth of C or if we're talking chords the V chord with the roman numerals to hopefully avoid confusion.
OK, Diatonic harmony. Basically we build chords by stacking thirds, or every other note of the scale so if we harmonize this scale we get
I ii iii IV V vi vii
C D E F G A B
E F G A B C D
G A B C D E f
The top letter is the chord name, C major is spelled CEG.
Capital letters above mean a major chord and minor for the small letters so its C major D minor, the saddest of all keys, E minor and so on. The vii is the oddball diminished chord but we're not going to worry about that now, thats a whole nother lesson.
If we add another third to the tops of these chord we get the diatonic seventh chords but again, whole nother lesson.
Right, back to playin lead. Dorian mode is a great place to start. First make sure you know the box pattern for this one starting on the first finger on the low E string. You can just use the major pattern and start one note up but then we're not expanding our mental fretboard map.
Got that..cool
OK so the same works with the chords, the i chord in Dorian is D minor, ii is E minor etc. everything just moves over a spot but Dorian is a very different sounding thing than Major.
Black Magic Woman is a diatonic Dorian song. If you ever learned the signature licks in the beginning of the song you might have noticed that you are playing of the C major scale pattern but we're in D minor. Whats up with that? Well simply it's because C isn't the root or home key, D is so now we're in Dorian mode.
i ---- IV v
D E F G A B C
F G A B C D E
A B C D E F G
The i, IV and v are the chords for Black magic woman, or D minor 7, g7 and A minor7.
So heres the point of all this. D Dorian has the same seven notes in it as C major so we can use either scale for our solos,
or any other mode in its natural key, natural key being the one it naturally falls into wit no sharps/flats. So for Black Magic Woman you could use G mixolydian, C major, D dorian...any of them. Obviously this is trickier when we get outside the natural keys but the relationships between the scales never change. Dorian will always be a whole step up from the major, natural minor will always be a minor 3rd down, Mixolydian will always be a fifth up etc.
Another example, Goin Down the Road Feelin Bad is in E Mixolydian, mixolydian is always a fifth up from its relative major scale so if we drop down a fifth, a power chord shape, we get A. So you could use A major or B mixolydian patterns here and still be playing the same seven notes, the same mode. Goin down the road and BMW are both diatonic their key but like was mentioned earlier not everything is.
Someone mentioned Scarlet Begonias in a previous post saying it doesn't work with B major because the E and A arent diatonic, arent naturally in that key. But let's "de-compose" that tune real quick.
the notes of the three chords are: B-D#-F# E-G#-B and A-C#-E and we know the key is B so lets arrange the notes starting on B. We get
B- C#- D#- E- F#- G#- A-
1 1 1/2 1 1 1/2
That is a major scale with a flat 7th, or Mixolydian mode so we can use that for this one or like we saw with GDTRFB, drop it down a 5th and we have E major or F# dorian or E Phrygian or F Lydian and so on. So Scarlet Begonias is diatonic B Mixolydian and the outside/sharp notes mentioned in the previous post are there now.
Damn, this went long, one last thing with the pentatonics. Dorian mode is the minor pentatonic plus 2 notes and the major is Mixolydian plus two notes so you can use those modes in place of the 5 note pentatonic scale to spice things up a bit.
Hope this helps, I know it helps me every time I pick up my guitar, but of course all theory applies to any instrument.
Rock on

Aint no time to hate....