There are few topics more useful to expanding one's musical ability than intervals. By studying intervals and visualizing them on the fretboard, you will expand your phrasing/melodic skills as well as your harmony (chords) skills since major and minor thirds are central to a lot of chord types (such as minor and major chords as you can guess!).
In this guitar lesson I will show you several exercises that will get you thinking about third intervals and which will also have you looking at scales with a fresh set of eyes. We won't go too deep into theory, but have a look at the theory section below if you need to freshen up on the idea behind third intervals.
A third interval, for the purposes of this guitar lesson is the space between three consecutive notes of a Major Scale. So if we consider a G Major Scale, which has the notes G, A, B, C, D, E, F#, we can start from G, and the third note up from G is B. In this case we have 2 whole steps, which means G to B is a Major Third Interval. So remember: Major Third = 2 Whole Steps.
If we continue to the next note in the G Major Scale - A - we see the third note from A is C, which is a one and a half step interval. This is a minor third: Minor Third = 1 and a Half Steps.
We could continue this way for each note and we would see that for every note in the Major Scale, there is a corresponding third interval that we can build from the given scale note- either major or minor third. We can see this on a staff as below:
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Above is not to be confused with harmonizing a Major Scale in triads (see my Triads Guitar Lesson if you are interested in harmonizing the Major Scale as triads). Where you see a letter without lowercase 'm', that means a Major Third, not Major Triad. Where you see a lowercase 'm', I am referring to a Minor Third, not a Minor Triad.
This means that for any given Major Scale, we can form either a major or minor triad. Specifically, we have the following:
| Major Scale Degree | Third Interval Type |
| 1 | Major Third |
| 2 | Minor Third |
| 3 | Minor Third |
| 4 | Major Third |
| 5 | Major Third |
| 6 | Minor Third |
| 7 | Minor Third |
That is all the theory we need to appreciate what is happening in this guitar lesson. In the exercises I will show you how to visualize third intervals on the fretboard which will go a long way in expanding your fretboard knowledge as well as your ability to navigate through scales in a new light.
