Tougher Common Tones

Notice that two tones of each chord stay the same:
C7 chord modulating to an A7 chord: C E G Bb
A C# E G
Now the A7 chord to the F# 7 chord: A C# E G
F# A# C# E
Now the F#7 chord to the Eb chord: F# A# C# E
Eb G Bb Db
Note: It is easier to think in terms of Eb rather than D#. The Bb and Db notes are enharmonically the same as the A# and C# notes.

Can you take this progression further?

More on Common Tones

So let's continue on the common tones of the F (Sub Dominant) chord in the Key of C. The notes are F A and C. But now, lets drop the F note to an E note which makes it a 2nd inversion A minor (E A C), and instead of that, let's raise the C note 1/2 step to a C# note (E A C#). This 2nd inversion A chord ends up wanting to resolve to a D Minor chord very nicely. The D Minor chord is comprised of the notes D F and A. The E note would resolve nicely 1/2 step to the F note, the A note would remain a common tone and the C# note would have a tension that would resolve nicely 1/2 step up to the D note. So this 2nd inversion A chord (not A Minor, but A) resolves nicely to a 1st inversion D Minor.

Or try this: Take the root position C chord, C E and G and raise the C note 1/2 step to C#. This makes a chord comprised of the notes C# E and G. This is a 1st inversion A7 chord. This resolves very nicely to the D Minor chord. This can also resolve nicely to the D chord (D F# and A) because the 7 note which is a G will resolve nicely to the F#. So C# E G resolves to D F#.

Common Tones

One of the many reasons why music flows so smoothly together is the use of common tones. Take for example the following: Pick the Key of C. The Tonic chord is comprised of the notes C E and G. Two of these notes also belong to the minor third triad in the key of C. They are the notes E and G. The minor third in its root position is E G B. This forms an E Minor chord. Dropping the C note down to a B note while leaving the E and G note still being played creates a 2nd inversion E Minor chord, B E G.
Another chord formed from the Tonic C E G, is the relative minor chord in the Key of C, called the A Minor chord. This is comprised of the notes A C and E. So from a C chord in its Tonic root position C E G, raising the G note to an A note creates a 1st inversion A Minor chord.
Take the Sub Dominant chord in the Key of C, the F chord, comprised of the notes F A and C. What could we do with this chord? How about going to an A minor? To do this, we would simply drop the F note to an E note. This would create a 2nd inversion A Minor chord: E A C.
I'll post more of these beautiful chords later. In the meantime, experiment.

The Five of Five Chord

In Nashville, many pickers call this chord the "2" chord and write it as a large Roman Numeral 2. But really, it's the five of five chord in music theory circles.
Most often times it appears in a tune either after the Tonic chord or after the Dominant chord. For example: in the key of "G", play a G chord (Tonic)and follow that with a C chord (Sub Dominant) then back to the G chord, then up to the A chord (Five of Five)and then to the D chord (Dominant, also called the "Five" chord). You can then resolve this by Playing these chords: G chord, C chord, G chord, D chord and finally, G chord.
Another way the Five of Five is used is: in the key of "G", play a G chord (Tonic)and follow that with a C chord (Sub Dominant) then back to the G chord, then to the D chord (Dominant, also called the "Five" chord)and then to the A chord (Five of Five) and back to the D chord. You can then resolve this by Playing these chords: G chord, C chord, G chord, D chord and finally, G chord.
The Five of Five chord works this way: The color tone of the Five of Five has a tension that resolves nicely to the base note of the Five chord. For example: think in the key of "G" again, the color tone of the Five of Five is a C# note which resolves nicely to the "D" note in the D chord. Or, it could resolve nicely, creating a little tension (which can later be resolved to the color tone of the Tonic), by going to the flatted seventh note of the Dominant chord (D chord in this example) which would be the "C" note. (This "C" note would eventually resolve to the "B" note which is the color tone of the G chord).

Another well used chord progression is from the Tonic to the Sub Dominant to the Five of Five to the Dominant and back to the Tonic.
Yet another neat chord pattern is to go from the Tonic to the Five of Five of Five ( think of this one as a relative minor chord made major by raising the color tone) then to the Five of Five then the Five and return to the Tonic. For Example in the key of "G": G; E (not minor, but major); A; D; G.

Now find and resolve the Five of Five chords for these keys: D; A; F; C

Circle of Fourths

Practicing a circle of fourths is great for ear-training and for remembering flatted sevenths. On your bluegrass stringed instrument of choice, sound out a C7 chord like this: C E G Bb. Notice the tension in the Bb note and how it wants to resolve to the A note which is the color tone of the Four chord: F A C. Now form an F7 chord: F A C Eb and notice how the Eb wants to resolve to the D note which is the color tone of the Bb chord. Here are the chords in the circle of fourths:
C E G Bb; F A C Eb; Bb D F Ab; Eb G Bb Db; Ab C Eb Gb; Db F Ab Cb (enharmonically the same as a "B" note); Now switch to sharps instead of flats to make it easier: F# A# C# E; B D# F# A; E G# B D; A C# E G; D F# A C; G B D F; and now you're back to the C chord.
Try this exercise over and over until it becomes second nature to hear these tensions and resolutions.

Flats and sharps as key signatures

As we've learned, a key signature with one sharp (F#) is the key of G. We know that the F# is the leading tone which raises 1/2 step to the tonic note. In the G Scale remember the notes G A B C D E F# leading into G. So if the key of G has 1 sharp and the key of D has 2 sharps (D E F# G A B C# leading into D) we see there's a pattern to this.
An easy way to remember sharps is this little saying: Fat Cows Go Down An Easy Bank.
An easy way to remember flats is: Be Earnest And Don't Get Cold Feet.

So when you run into a key signature with 5 sharps, you can say Fat Cows Go Down An (and stopping right there at 5 words of our saying, you'll know the A# is leading 1/2 step to the tonic, which is B, therefore 5 sharps is the key of B.

With flats, it's a slightly different formula. Say your music has 3 flats. The saying is: Be Earnest And (right here at the 3rd flat, you "stop and drop". So Bb Eb and Ab, you simply go back to the previous flat for the proper key signature.
1 flat = F; 2 flats is Bb; 3 flats is Eb; 4 flats is Ab; 5 flats is Db; 6 flats is Gb and 7 flats is Cb. Also notice how they climb by fourths. F to Bb is a fourth; Bb to Eb is a fourth and so on. Sharps climb by fifths.