A sticking point for arises for many guitarists when attempting to solo over changing harmonies.  A straight forward approach of matching one scale to one key is effective when improvising over many rock tunes, but when it comes to the more sophisticated approach of matching your scale choice to the chord of the moment, many guitar players can become lost.  And of those who can make the changes, many have difficulty continuing their ideas through the shift in harmony, instead producing a series of disjointed melodies.  By starting with simple chord progressions, limiting one’s self to the pentatonic scale and employing a few exercises to continue phrasing across the bar line, guitar players can begin to see chord changes not as an obstacle to melody, but as an opportunity for its creation.

Among the most common harmonic progressions is the simple I-IV (the tonic or first chord in a key to the subdominant or fourth chord in the same key).  In the guitar friendly key of A, this is an A chord to a D chord.  We will alternate each for two measures in this progression to give ourselves ample time to anticipate and accommodate the shift.  The progression looks like this on paper:

|| A   | A   | D   | D :||

While a variety of scale choices are available over each of these chords, for the sake of simplicity in this exercise, we will limit ourselves to the pentatonic scale constructed from each root (aka the A major pentatonic and D major pentatonic scales).  These scales are guitar-friendly and provide enough contrast between chord tones and scale tones for the creation of an interesting melody.  You might notice there is only a one note difference.  See the attached PDF for a diagram of both scales in each position (I recommend you print this out).  I have also embedded backing tracks over which you should perform this exercise.

Let’s begin applying these scales over these changes in an exercise which limits ourself to the second position patterns (the first of each scale) and focusing on shifting between one scale and the next with the smallest possible leap, while maintaining the direction of the melody.  We’ll start at the lowest note of the A pentatonic pattern and begin ascending the scale in quarter notes.  After two measures, when we reach the change to the D chord, shift to the next highest note in the D major pentatonic scale and continue ascending.  When you reach the top of the pattern, turn around and begin descending, shifting smoothly back to A when the harmonic change occurs.  Continue this exercise until you can perform it without conscious effort.  The first sixteen measures should look like this:

I advise performing this exercise first without a metronome, simply counting two measures and then performing each shift in order to train your mind and hand to execute the change in scale.  Then move to doing it over a metronome at a slow tempo.  Once you capable of that, move on to performing it over the backing track, slowing down the tempo if necessary. 

Once this is comfortable, switch the rhythmic subdivision to eighth notes and execute the same exercise.  The first eight measures should look like this: 

This exercise can be taken to another level with the use of sequences, but for now, this should be adequate to begin improvising.

When improvising, remained limited to the second position scales we had been using previously.  At the change between chords, aim to maintain the integrity of your lines, continuing in the same direction and with the least possible leap in pitch.  Resist the urge to simply start a new line from the root of the new scale.  Be sure to include adequate space in your phrasing and avoid becoming disjointed by only including it at the chord change.

This exercise should be repeated in every scale position until it is fluid for the sake of thoroughness.  If you only perform in your favorite or more familiar positions, when you are improvising your runs will hit a wall.  Once it is comfortable in every position, spend some time improvising over whole neck, creating smooth shifts at the bar line.

How To Use The Track:

This track is broken into three two-minute sections.  Perform the following once in each scale position

Section 1: Perform the quarter-note shift exercise.

Section 2: Perform the eighth-note shift exercise.

Section 3: Improvise smoothly between the two scales.

If you get lost on the first two sections, start over from the bottom of the A scale and resume the exercise.  Aim to keep the exercise going for the whole two minutes.

A I-IV changes