We have discussed intervals thus far in terms of their applicability as an alternative labeling scheme for major scales. From there we have examined how they allow us to retain pitch relationships while changing keys, thus allowing us to create moveable chord and scale shapes that we can apply in any key by simply moving the whole scale or chord to the appropriate location along the fretboard.
We will now consider them more closely in terms of their function in assisting us toward establishing shades of mood. Recall that we have two fundamental components of music, pitch relationships and time relationships, which we combine in various ways to achieve compelling flows of tension and release. It is needful then to understand the function of each interval to allow for maximum creative power. Besides helping us to build and embellish chords, an understanding of interval qualities can help us with choosing effective resolving notes for solo phrases, and we can also use the intervals themselves as a sort of intermediary between notes and chords. We have seen this with Power Chords, which are simply perfect fifth intervals.
Our understanding of interval function starts with the idea that the first interval is the baseline or reference interval. The sound qualities of the successive intervals are understood to be in relation to the first interval. There are only five fundamental sound qualities of intervals: perfect, major, minor, diminished, and augmented.
1 - perfect (in relation to another first interval note)
b2 - minor
2 - major
b3 - minor
3 - major
4 - perfect
b5 - diminished
5 - perfect
b6 - minor
6 - major
b7 - minor
7 - major
8 - perfect
Let now consider the intervals that occur beyond the octave. At the octave we have an interval that corresponds in pitch and feel to the first interval. From there each of the successive intervals also corresponds to its counterpart in the previous octave, such that the 9 is equivalent to the 2, the 10 equivalent to the 3, etc. Likewise, the moods of each post-octave interval will correspond to their sub-octave equivalents. We refer to these intervals beyond the octave as compound intervals.
The Minor Seven Flat Five (Half Diminished) Chord is similar to a Minor Seventh Chord, but with a flat fifth interval in addition to a flat third and flat 7. It is also commonly referred to as a Half-Diminished 7th Chord. It is sort of a "beyond minor" chord, very tense sounding chord in the same way that the Dominant 7 chord sounds tense, but the Minor Seven Flat Five sounds even more tense than the Dominant Seventh. As such, it is useful as a substitute for the Dominant Seventh as a V chord, or as the ii chord in a minor chord progression. You will see this chord labeled as m7b5, half dim7, or Ø7
8 - perfect
b9 - minor
9 - major
b10 - minor
10 - major
11 - perfect
b12 - diminished
12 - perfect
b13 - minor
13 - major
Note that our interval quality charts so far have not mentioned the augmented interval quality noted in the introduction. We discussed previously in the course the concept of enharmonic equivalents – same note, two possible labels depending on context. Intervals follow a similar set of rules.
Perfect Interval expanded by one half step yields an Augmented Interval
Perfect Interval contracted by one half step yields a Diminished Interval
Major Interval expanded by one half step yields an Augmented Interval
Major Interval contracted by one half step yields a Minor Interval
Minor Interval contracted by one half step yields a Diminished Interval
Common Applications of Intervals for Guitar (Double Stops)
As mentioned above, we can also use the intervals themselves as a sort of intermediary between notes and chords. We have seen this with Power Chords, which are simply perfect fifth intervals. Here are fingerings for some of the other useful intervals. Note that the shape of the interval fingerings changes across strings 3 & 2 since these strings are tuned a major third interval apart, in contrast to all of the other strings pairs which are tuned a perfect fourth interval apart. When we play these intervals in harmony (at the same time) we call them double stops.
For pleasing application of the third and sixth intervals double stops as solos/fills we must consider two additional important factors. First, third intervals are simply two of the intervals of a major triad chord 1-3-5. So we play third intervals as if they are a subset of the sequence of chords dictated by the major scale harmonizations ... major-minor-minor-major-major-minor-diminished, bearing in mind that the third interval corresponding to the diminished chord corresponding to the v° chord will simply be a minor third interval since the flat five is not included.
Second, sixth intervals do not play well as such. Rather they sound best when used as inversions of their corresponding third intervals. So once you understand the fretboard geography of the third intervals, you can play the sixth intervals as inverted opposites of the third intervals - minor-major-major-minor-minor-major-major.
For pleasing application of the fourth and eighth (octave) interval double stops as solos/fills we must consider that these are perfect intervals and thus do not do not have a major or minor quality. Therefore, the fingerings for them remain the same regardless of which chord they correspond to in the major key scale harmonization. The fourth intervals have an aggressive feel and thus are more useful as fills in higher energy styles such as Rock, whereas the octaves have a more smooth feel and are thus more applicable to lighter styles such as jazz. However, musical "rules" are alwasy subject to artistic license, so experiment with these and you will find the best way to use them in expressing your own musical sensibilities.