The four fundamental building blocks of music theory are major scales, keys, intervals, and triads. Understanding intervals, although not too difficult, will be a lot easier if you already know how to construct major scales and you know the key signatures for all fifteen major keys. If you’re not completely familiar with either of those topics, a bit of review will sure be helpful. If you know nothing about either, that’s okay – hopefully, the following discussion will spur your interest and prompt you to expand your music theory knowledge.
So – what are intervals in music? Usually, an interval is defined as the distance between any two notes, however, it’s better to think of it as the relationship between two notes, or pitches. The distance is measured by the number of half-steps (semitones), and you’ll soon find that it becomes rather cumbersome trying to remember how many steps there are, especially for larger intervals. It’s much easier to use a major scale and letter name approach, hence the relationship reference. Understanding intervals can be a little tricky, so let’s simplify the subject as much as possible.
Every interval has two names – a general name and a specific name. The general name indicates the numerical comparison (ordinal positions in a major scale) and basic size of the interval. The specific name defines the sound quality and represents the exact size of the interval. When two notes are played or sung successively, it’s termed a melodic interval; two notes sounded simultaneously form a harmonic interval.
Identifying an interval, either melodic or harmonic, is always based on how the upper note relates to the lower note. This is why understanding major scales is so important. If the upper note belongs to a major scale built on the lower note, the interval will be either a major interval or a perfect interval. Hopefully, you remember from previous lessons that the 2nd, 3rd, 6th, and 7th degrees of the scale are labeled as major, while the 1st, 4th, 5th, and 8th degrees are labeled as perfect. If the upper note is altered either down or up from its position in the major scale, the resultant interval will be minor, diminished, or augmented.
Of course, the size of an interval can be contracted or expanded by raising or lowering the bottom note, too, with the same result. But, to maintain key integrity, we’re only concerned with movement of the upper note for this lesson. Altering the lower note will change the key, and we don’t want that. Confused yet? Admittedly, you should be, but hopefully, it will soon make sense – trust me!
Remember, every interval must have a number (general name) and a quality (specific name). Actually, that’s not exactly true – a ‘1’ is called a prime or unison, and an ‘8’ is called an octave, but think of them as numbers anyway! If you don’t automatically know all of the major scale notes in every key, which most guitarists probably don’t, it’s pretty easy to figure out an interval’s number. Just use your fingers to count through the musical alphabet. For instance, if the low note of an interval is some sort of an A and the upper note is some sort of an F, then the number will always be six. Then you must figure out how the accidentals, if any, define the real interval name.
What determines the quality, or specific name of an interval? If the size (or distance) of any major interval is reduced by one half step, it becomes a minor interval. For example, C to E is a major 3rd; C to Eb is a minor 3rd. Reducing it another half-step results in a diminished interval – the Eb is lowered to Ebb. In the key of A, F# represents a major 6th, F is a minor 6th, and Fb is a diminished 6th. Theoretically, yet very rarely used, doubly diminished intervals exist as well, but you’ll never see a triple flat unless you’re playing an obscure classical piece.
Increasing the size of a major interval by one half-step results in an augmented interval, and you’ll use some of them quite often. An augmented 3rd in the key of C becomes E# (looks like F, but it isn’t); an augmented 6th in the key of A becomes an Fx (looks like G, but it isn’t). A great example is the Hendrix chord (Purple Haze), otherwise correctly named an E7#9 chord. You probably know this one! In your mind, picture the most common guitar finger formation in the sixth fret – the notes are E, G#, D, and Fx (double sharp). The fifth of the chord is left out since it really doesn’t add anything. The uppermost note on the second string looks and sounds like a G, doesn’t it? Well, it’s not – it’s really an augmented 9th. The ninth note of an E major scale is F# and it has been raised one half-step to Fx. The 10th (same letter name as a 3rd) hasn’t been lowered by a half-step, so it can’t be a G – there’s no such thing as a flatted or minor 10th chord!
Does it really matter what you call that note? Yes, it does! Will it sound any different? No, it won’t, but learning how music theory really works will serve you well in the long run. As I’ve stated in previous lessons, music theory is all about letters, numbers, formulas and patterns. Understanding intervals for guitar is no different.
Thus far, we’ve only discussed what happens if you alter a major interval. What about perfect intervals? As you may also remember from my previous music theory lessons, the term ‘perfect’ was used by ancient Greek theorists to represent sound wave ratios and consonant melodic and harmonic development. It really means the same thing as major except that, when reducing the interval size by one half-step, the minor designator is skipped and it goes straight to the specific name ‘diminished’. So, in the key of C, the perfect fifth, G, becomes a diminished 5th when lowered to a Gb – not a minor 5th. A doubly diminished 5th is Gbb. Upward movement of the top note remains the same – raising a major interval by a half-step is an augmented interval. Raising a perfect interval by a half-step is an also an augmented interval. Again, doubly augmented intervals are possible and you might encounter them once in awhile -- most likely on a college theory test! So, don’t worry about it – they’re rare.
When reviewing the handy interval charts (below), please keep in mind that some theorists dispute the validity of triple flats and triple sharps. The latter don’t occur in the key of C, but they can in other keys like F# or C#. Doubly diminished primes are another point of contention as it doesn’t seem logical that the altered upper note of the interval can fall below the original lower note. Good point, really. Just because something is theoretically correct or possible, it doesn’t mean it’s also practical. Understanding intervals requires a little thought, which is always a good thing!
The first two flow diagrams show how the interval name changes as the upper note is raised (to the right) or lowered (to the left) while the lower note, or root remains constant. The spreadsheet chart shows the possible intervals within a one octave range in the key of C.
Music Theory for Guitar (part 5) - Understanding Intervals II