The nature of the guitar fretboard allows the fretting hand to move in a myriad of angles. It can move parallel to (or along) the strings. It can also move perpendicular to (or across) the strings. And by switching strings and shifting positions at the same time, it can also move in a diagonal direction. Each angle of movement opens up new sounds and techniques. In order to fully master a scale so that it can be played freely, guitarist must learn to perform every scale from each possible angles.
The most basic method of exemplifying horizontal scales is by learning to perform the pentatonic scale in this manner. Since it’s impractical to perform a scale entirely on one string, we will divide the neck into pair of strings and create shapes based on what notes can be played in each position. You can see the first shape in A minor below.
If we line up all the cells notes on adjacent string sets, we end up with this:
To perform these cells ascending, we will play the notes on the lower string ascending followed by the notes on the higher string ascending, before moving up to the next cell and repeating the process. To play these cells descending, we will take the opposite approach, performing the notes on the higher string descending, followed by notes on the lower string descending, before moving down to the next cell. This approach is depicted for each string pair on the final pages of this document. You will notice that this method creates a natural sequence and, indeed, horizontal movement is excellent for creating sequences. Play each example with a metronome until it is comfortable and familiar. Then spend a specific amount of time (1 to 2 minutes) improvising using each string set over a backing track in A minor. Once you have done this for each string set, spend some time improvising freely while loosely focusing on the concept. After performing this process in A minor, begin repeating it around the circle of fifths, figuring out the structures for each key. Don’t be afraid to write them down if you need.