Intervals I
Up until now I've been using terms like Perfect 5th and ♭3 in the hope that the reader might have some understanding of what they might mean.1 However, in order to help us understand some of the material we'll have to deal with in future articles, we'll need to formalise some of this. Rather than bombarding the reader with a slew of dry statistics, I'll introduce these a few at a time.
But first, what do we mean by the term ‘interval’. Basically, an interval is a way of describing the difference in pitch between two notes.
The smallest interval we usually deal with is the semitone, which exists between any two notes on the same string of a guitar that are a single fret apart (the main motif of the ‘Jaws’ theme is a good example of what two notes a semitone apart sound like). We will define other intervals by the number of semitones they are equivalent to.2
We'll concentrate on the most obvious intervals from the shapes we've covered so far, namely the Major third, the Minor third and the Perfect fifth (we'll come to the others in due course). Don't worry too much about what the names mean (again, we'll come to that). The important takeaways from this lesson are
- Knowing how many semitones each of the intervals comprise,
- Knowing how they lie on the fretboard (there's usually more than one way) and
- Becoming familiar with what they sound like
- melodically, i.e. when the individual note are played one after the other either:
- ascending: where the lower of the two notes is played first
- or descending: (I'll leave this definition as an exercise for the reader.)
- and harmonically where both notes are sounded simultaneously3
- melodically, i.e. when the individual note are played one after the other either:
So without further ado, here are the definitions for our first three intervals.
| Number of semitones | Abbreviation | Scale-degree / chord-tone | |
|---|---|---|---|
| Minor third | 3 | m3 | ♭3 |
| Major third | 4 | M3 | 3 |
| Perfect fifth | 7 | P5 | 5 |
(We'll explain the differences between the second and third columns in a little while.)
The Major Third
Given our definition, “Four Semitones”, the most obvious way to invoke this interval on the guitar is to play two notes four frets apart on the same string. While that is a perfectly valid approach to playing a M3, we're going to concentrate (for now) on the version that spans two strings:
The Minor third
We'll consider two ways of playing this interval. First, the obvious one:
And now the two-string version:
The Perfect Fifth
We'll also consider two ‘versions’ of this interval, one (familiar to many of us as the mighty ‘power-chord’) which span two strings:
and one that spans three strings:
Now take some time to see how many examples of each of these intervals you and find in the major and minor shapes we've looked at so far.
The most obvious examples are the M3 between 1 and 3 in the major shapes; the m3 between 1 and ♭3 in the minor shapes; and the P5 between 1 and 5 in all the shapes (this one appears in both its forms). Notice how this correlates with the last column in the table above.
“So why haven't you included the numbers in these diagrams?” Well, although that might make sense where the lower note represents note 1 in a chord, scale etc, this only sometimes the case. E.g. in a major chord, there is a m3 between 3 & 5; and in a minor chord, there is a M3 between ♭3 and 5. Calling ♭3 ‘1’ would help no-one...
As per the table above, I tend to use one notation for intervals proper and another for notes within a structure (chord,scale etc.) The latter describes the note's relationship with the ‘root’ or ‘tonic’ of the structure (i.e. note ‘1’). This is the notation I've been using in the chord diagrams).
The interval notation uses a letter4 (known as the ‘quality’) and a number (known as the ‘size’) while the other uses the number and assumes a major or perfect quality which can be altered by preceding it with a ♭ or a ♯ sign (or, very occasionally, something else.) Don't worry too much about the technical details at the moment, they will begin to make more sense in time.
Not everyone distinguishes between the two types of notation in this manner, so you'll find both systems (and others) being used for both purposes. I think being able to describe a scale as 1 2 3 ♯4 5 6 ♭7 and using terms like m3, P5 etc. to describe the interval found between any two of its members is very useful and helps avoid ambiguity.