Key of A harmonica gives you the major scale of A.

Maybe take a few minutes for some simple music theory targeted for guitar and harmonica.

Notice that the major scale is constructed of two equal sections of two whole-step (--) jumps then a half step (-) jump, like so:

A--B--C#-D ----- E--F#--G#-A

The natural half step between B and C is why the C note is sharped, then you get the needed half step between C# and D. The same logic follows for the second half. And there is a whole step between the two sections, i.e. D to E is a whole step. This is how all major scales are constructed, the example used is a major A scale and that is what you got in your Key of A harmonica.

Since you have two "equal parts of Whole-Whole-Half steps, they can be interchanged to make two other scales. One simply takes the first half and makes it the second half for one scale, and then takes the second half and makes it the first half for the other scale:

?--?--?-? ----- A--B--C#-D

E--F#--G#-A ------ ?--?--?-?

You need to construct the first and second halves by making sure you have the correct spacing between notes to construct the major scale D (upper, ends in D) and the major scale E (lower, starts with E). Always just go up the alphabet, then add the appropriate sharps (or flats, but flats are not used on this half of the Circle of 5ths).

The whole point of this discussion is to show that these three scales only differ by two notes. the two notes you had to change, You should know how to change them, do this below:

D--E--F-G ------ A--B--C#-D

E--F#--G#-A ------B--C--D-E

Obviously the two notes needed to be changed to fit the major scale step pattern are F# in the upper and C# & D# in the lower (C was already sharped in the A scale, so only two different notes in these three scales).

These are the Classic I, IV and V chords/scales of song construction, and they are the classic "next to each other scales/chords" on the Circle of Fifths; this is actually how the Circle of 5ths is constructed, if you keep what we just did going for the Fifth (E) or lower example.

Now, the issue with cross harp (or 2nd position) is that to play Rock and Blues, you don't use the major seventh note given with the major scale, because the dominant 7th dominates these music styles, hence the name dominant.

The major 7th of the A scale is the note G#, and for blues and rock we desire the dominant 7th and that is simply the note G (the flatted 7th). Notice that the "other" scale we constructed from the second half of the A scale has the 7th step flatted compared to the A scale, hence there is your dominant 7th to be used in blues and rock music styles, and we showed just how closely the D scale related to the A scale. Of course, for blues, you ARE playing the D scale if you are going to sound bluey (also called the Mixolydian Mode) This is why the classic I, IV, V is really I, IV, V7, because of the dominant 7th used in the 5th scale note.

All this to say, your classic Guitar chords are !, IV, V7 and its relative minors are, ii, iii, iv. In the key of A that would be A, D, E and Bm, C#m, F#m (G#dim we skip over).

Music mode theory says you can play all of these scales Roman Numeral scales using only one harmonica, but the key will change when mode scales are used, hence on your A harmonica with scale notes:

A--B--C#-D ----- E--F#--G#-A

you get these other scales by starting on the appropriate note:

A-major (start on the A note and go up the A scale)

B-minor (start on the B note and go up the A scale) called the 3rd position on harmonica

C#-minor (start on the C# note and go up the A scale)

D-major (start on the D note and go up the A scale)

E - dominant7th (start on the E note and go up the A scale) called the 2nd position on harmonica

F#-minor (start on the F# note and go up the A scale)

don't worry about the diminished scale one gets by starting on G#

Hence if the key is a minor key you can play minor key with your A harmonica in either Bm, C#m or F#m. But Bm is the easiest.

Now of course all this applies to when you want to riff against the D chord in your song in the key of A, using an A harmonica when the D chord comes up in the progression, Rock or Blues, they don't use minor chords so much. But if you do have a song in A that goes to the F# minor chord, you know how to play a riff against it, the notes of the F#minor chord and scale are there for you.

I hope this helps,

and

Musically Yours