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Instead of going on with the remaining perfect intervals, the fifth and fourth, I am moving on immediately to thirds. Thirds are the building blocks of Western harmony. Triads and seventh chords are built from thirds. For this reason, thirds deserve a special place.
There are two basic kinds of thirds: major and minor. Both of these intervals are consonant, but they are not considered perfect. Thus, musicologists call these imperfect consonant intervals. A third is always covers two scale steps. Thus, if you start at G, the third above it is always some kind of B. If you start at C, the third below it is always some kind of A. And so forth…
Major Third
A major third spans four frets on the fretboard. Another way to put this is that it includes four half-steps.
A pure major third is the fifth partial harmonic, and you can play a pure major third by playing the harmonic just behind the 9th fret. The frequency ratio of a just major third is 5:4, and that’s what you will hear when you play the harmonic.
In equal temperament, the major third is a little wider than the just major third, which explains why the harmonic is played a little behind the 9th fret. The harmonic is a little bit flat of the equally tempered third.
This difference actually becomes important when playing the blues, because you will often bend the minor third in blues, and when you do, it is usually a good idea to leave the bend just a little flat. You will be bending to the pure major third, not to the equal tempered major third, and that often sounds better.
When the Saints Go Marching In and Kumbaya are two songs that begin with an ascending major third.
Swing Low Sweet Chariot and Summertime both begin with descending major thirds.The attached file shows the five open major third voicings, and the closed voicing pairs for major thirds. Notice that there are only two shapes for playing major thirds.
Minor Thirds
A minor third spans three frets, or three half steps.
The pure minor third is the 19th partial harmonic, which is pretty far up in the harmonic series. I’m not aware of any guitar where you could effectively play this harmonic. It’s pure frequency ratio is 6:5, which involves pretty low numbers, and explains why it is a consonant interval.
Also, the pure interval is remarkably close to the equal tempered interval. It is flat by only 2 cents (that is 2/100ths of a semi-tone), a difference that is undetectable by most people. (Compare that to the major third, which is off by 14 cents).
Georgia on My Mind, and the opening riff from Whole Lotta Love both begin with ascending minor thirds.
Hey Jude and The Star Spangled Banner both begin with descending minor thirds.The attached sheet shows the open and closed minor thirds on adjacent strings. Again, notice that there are only two shapes for playing minor thirds, one for the second and third string, and the other for the other four adjacent pairs of strings.
Happy and Sad
Some people will claim that a major third is a happy sound and the minor third is a sad sound. There is an extent to which this is right when talking about keys and scales. Less so when talking about chords, but its still useful. When talking about an interval, however, it is simply not true. I will prove my point this way.
Take out your guitar and play the open high E string together with the B string at the fifth fret. Play a triplet. Now slide your finger back to the third fret, play the triplet. Now the second fret, triplet. Now the first fret, and triplet again. Always let the high open E ring out. This is a distilled blues turnaround.
When you play the B string second fret and the open E string, thats a minor third interval. But the sound is happy at that point. When you move it back to the first fret on the B string, you are playing a major third interval, but the sound has become sad. This has to do with the context of what you are playing, which creates the mood. What we hear in this passage is an implied movement from the A major triad (we are hearing the 3rd and fifth of that chord) to the A minor triad (again hearing the third and the fifth). Thus, we hear happy and then sad, although the intervals we hear go from minor to major.
The important point to take away from this is that an interval, by itself, has no emotional character whatsoever. It gets its character from the context in which it is used.
Harmonized Thirds
Soloists will often play sections of their solos using double stops in thirds. It’s a good idea to learn the harmonized major scale in thirds on each pair of strings. Notice that you will only have to learn two patterns to do this. And for those patterns, there are only two chord shapes.
A slight wrinkle occurs, because you can start your scale with the tonic on either the top note of the pair or on the bottom note. This only changes your starting point in the pattern. The pattern is always the same. I have also attached a sheet which shows harmonized C major scales in thirds for each pair of strings. You can change this to any other key by moving the starting chord up or down the neck. For example, start the pattern two frets higher, and you are playing the harmonized D major scales.
Brian has used a lot of harmonized third patterns in his lessons. Most notably, there was lesson EP157:
Harmonized Lead Guitar Lesson (Latin / Hawaiian Style) – EP157
But the James Burton lesson has some extended harmonized third passages, notable at the beginning and bars 17-20:
And it appears in many other lessons as well (EP001 has a harmonized scale passage, too, for example).
Finally, the complementary interval of a major third is a minor sixth, and of a minor third is a major sixth. I haven’t treated augmented or diminished thirds here. A diminished third is a half step smaller than a minor third (say from E to Gb), which sounds the same as a major second. And an augmented third is a half step larger than a major third, (from E to G##), and sounds the same as a perfect fourth.
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