Most of western music is built upon the major scale, and there is a great variety of sound which can be derived from it. In an attempt to keep things simple, I will first explain how to construct a major scale on a single string, but not before adding a little theoretical background and terminology.
A scale is a set or series of notes, which when ascending, will for our purposes start on the “root” and conclude with the “octave.” Think of the root as the letter used to define what key you’re in, and a reference point from which all other notes are derived. As for the octave, this note is the same as the root, only higher in pitch.
As you may have gathered, the “oct” in octave implies eight. With few exceptions, the octave will typically be the eighth note of just about every scale you’ll encounter, but this is not really it’s defining characteristic. A major scale only has seven distinct notes, and the octave is just a higher instance of the root.
To illustrate, an octave is a note which is double your initial reference tone in hertz. For example, “middle A” is generally agreed to be 440hz, whereas it’s octave would be the next highest “A” at 880hz. Even though the frequency has doubled, it will essentially sound the same, only higher.
Now that we know the first and last notes of a major scale, how are the remaining six divided between these two points? To answer that, I need to first define whole and half steps.
A half-step is simply an adjacent note from a given reference point. For instance, a half-step up from A, is A#; and a half-step down from A would be Ab. A half-step can also be referred to as a semitone.
A whole-step is a note which is two chromatic notes from a given reference point. In fact, a whole-step is comprised of two half-steps. So a whole step up from A is B, and a whole step down from A is G.
Now, with the theory above in mind, you can construct a major scale with the following series of tones. This is something you will probably want to commit to memory, as it will help you navigate the scale.
whole-whole-half-whole-whole-whole-half
At this point you may be asking, what does all that gobbledegook mean? Well, WWHWWWH is the series of tones that comprise a major scale. Study the diagram below for clarification, by noting the intervalic distance between each note.
Next, apply this knowledge to a single string and play a major scale up and down the neck. As you get more comfortable playing this pattern, experiment with improvised melodies or “licks”. It is good practice to hum the intended melody as you’re playing. This practice helps reinforce an intuitive connection between the sound you imagine in your head and the muscle memory of your hands. Also, as you improvise with the major scale on a single string, think of the number or interval associated with each note. This will help prevent you from losing your place.
Once comfortable with this pattern, repeat the scale up the neck one octave higher, until you run out of frets.