Intervals describe the distance between two musical notes that are played together.
They can be classified according to their size (also called quantity), which is the number of scale notes between the two notes, and quality, which is how many semitones (or half-steps) are between the notes. They can further be described as melodic or harmonic, which describes whether the notes are played at the same time or one after another.
Melodic vs Harmonic Intervals
The first term you should probably learn about with intervals is whether they're melodic or harmonic. This is just a fancy way of saying whether the notes are played one after another or at the same time. Melodic intervals are two notes that are sounded one after the other. Harmonic intervals is when the two notes are sounded together at the same time.
Interval Size (Quantity)
Interval size refers to the number of steps in the scale between two notes, and these are just given a number.
The C major scale, for instance, is comprised of the notes C, D, E, F, G, A, B, and C. Playing the root C note with with each of the other notes gives us the following sizes:
Simple Interval Sizes (Unison through Eighth)
1. Unison interval: (C and C) - If you play two C notes at the same time (like on a stringed instrument or with multiple instruments)
2. Second (C and D)
3. Third (C and E)
4. Fourth (C and F)
5. Fifth (C and G)
6. Sixth (C and A)
7. Seventh (C and B)
8. Eighth (C and the C from the next octave higher)
Compound Interval Sizes (Ninths through Twelfths)
When describing interval sizes, we can keep going beyond an eighth too. Intervals larger than an octave are called compound intervals and we generally refer to the ninth through twelfth as these. Playing the C and D in the next octave up gives us a ninth which is just a compound second. Going one step further (C and E) gives us a tenth which is just a compound third.
As a rule of thumb, once we're beyond 12, we generally revert back to the simple interval name. For example, when describing the interval of a C with the B from the next octave up, we typically wouldn't call this a fourteenth, but rather a seventh.
Interval size can be described from any note to any note
Playing in the same key of C major, you can use these same size descriptions for the distances between any of the other notes as well. For example, a third from G is B. A third down from G is E.
But wait, some intervals can be described by the same size, but they have distinctly different sounds. In the key of C major for example, the interval of C and E can be described as a third, but so can an E and G, but these intervals sound quite different in quality. If you count the number of keys on a keyboard between these notes, you'll see that the C and E have one more note between them than the E and the G. This brings us to interval quality, which describes the feel of the interval, or more specifically, the number of semitones (half-steps) in the interval.
Interval Quality - Major, Minor, Perfect, Diminished and Augmented
Quality refers to the tonal characteristics of an interval. By ear you'll be able to distinguish these by the feeling of their sound, and this feeling is determined by the actual number of semitones (half-steps) between the notes.
Major Intervals
Major intervals can be seconds, thirds, sixths, and sevenths in size (or compound intervals that are multiples of these). They have a bright and upbeat feel.
The rule for a major interval is that the top note must be in the major key of the bottom note.
You'll often see major intervals represented with a capital "M" followed by the size of the interval, like M3 or M6.
Minor Intervals
Minor intervals are like major intervals in that they can be seconds, thirds, sixths and sevenths in size, but they are one semitone smaller than the major interval of the same size. In a minor interval, the top note is NOT in the major key of the bottom note.
For example, looking at the minor third of E and G, we see that G is not contained in the key of E major.
Minor intervals are often denoted by a lowercase "m" followed by the size of the interval like m3 or m6. The lowercase "m" reminds us its a semitone smaller than the major interval of the same size.
Perfect Intervals
A perfect interval can be unison, fourths, fifths or eights (or the compound intervals of these). The rule for perfect intervals is that the top note is in the major key of the bottom note and the bottom note is in the major key of the top note.
Perfect intervals are often written as capital "P" for perfect, followed by the size of the interval such as P4, P5, or P8.
Diminished Intervals
Diminished intervals are intervals that are one half-step smaller than minor or perfect intervals. You can diminish a minor second, minor third, perfect fourth, perfect fifth, minor sixth, minor seventh, or perfect eighth interval.
Diminished intervals are written as a lowercase "d" followed by the interval size, such as d5 or d2. The lowercase "d" reminds us its a semitone smaller than the minor or perfect interval of the same size.
Augmented Intervals
Augmented intervals are one half-step larger than major or perfect intervals. You can augment a major second, major third, perfect fourth, perfect fifth, major sixth, major seventh interval, or perfect eighth interval.
Augmented intervals are written as an uppercase "A" followed by the size of the interval. You guessed it, the capital "A" reminds us its a half-step larger than the major or perfect interval of the same size.
You may have noticed some overlaps (enharmonic intervals)
One thing that can be a little confusing when learning about diminished and augmented intervals is that there are often multiple ways of describing the same interval. A diminished third is just a major second. A diminished fourth is just major third. An augmented second is just a minor third, etc.
These are called enharmonic intervals and yeah, there are a lot of them. Don't sweat this for now. As you progress in music theory and especially reading music, you'll see that there are situations where it makes more sense to use one description over the other.
For now, just remember that a diminished interval is one half-step smaller than a minor or perfect interval, and an augmented interval is one half-step larger than a major or perfect interval.
Inversions of Intervals
Inversions are when you take the bottom note and make it the top note by moving it an octave up, or when you take the top note and make it the bottom note by playing it an octave lower. You will notice that doing this changes the interval.
Inverting an Interval Changes its Size
- 1 inverts to 8 (and 8 to 1)
- 2 inverts to 7 (and 7 to 2)
- 3 inverts to 6 (and 6 to 3)
- 4 inverts to 5 (and 5 to 4)
When you're talking about inverted intervals with other musicians and want to make sure you've calculated the new interval correctly, remember: the sum of the original interval and the new interval always add up to 9.
Inverting an Interval Also Changes Its Quality
- Major intervals invert to minor (and the opposite).
- Perfect intervals always invert to perfect intervals.
- Diminished intervals invert to augmented intervals (and the opposite).
Consonance and Dissonance
Music is the push and pull of the listener's ear and mind through the story of a song. There are intervals that are easier for us to listen to than others. This is where consonance and dissonance come in.
Consonant intervals are easy to listen to. They're a stable place for the listener and feel pleasant. Dissonant intervals are the opposite, they're harder to listen to and tend to push and pull the ear toward wanting to resolve to a consonant interval.
Consonant Intervals
Consonant intervals are the intervals that we find in major triads (if you don't know what a major triad is, don't worry, we'll get there soon). They are P1, P8, P5, M3, m3, M6, m6, and P4 (sometimes -- depending on the scale).
We can further break down consonant intervals into perfect consonances and imperfect consonances. Perfect consonances are the MOST stable sounding intervals, and imperfect consonances are less stable sounding.
Perfect consonances are the P1, P8, and P5.
The listener feels most grounded in the music when listening to these intervals. They're often used at the beginnings and ends of musical phrases.
Imperfect consonances still feel comfortable, but less stable than their perfect consonance counterparts. They're often used in places where the music continues on until it arrives at a perfect consonance. These are the M3, m3, M6 and m6.
Dissonant Intervals
If an interval is not a consonant interval, it is dissonant interval. These are challenging for the ear to listen to, and they beg to be resolved to a consonant interval. They're used for passage and transition in melody and harmony.
Dissonant intervals are the M2, m2, M7, m7, and all augmented and diminished intervals.
The Perfect Fourth (P4)
This is an oddball interval in that depending on the context of how its used, it can work as a consonant or dissonant interval. This depends on the other notes used around it. When it functions as the inverted fifth of a chord, it tends to be consonant. Otherwise, it lends more of a dissonant feel to the music, pushing for some resolution.
Tritones and their resolution
A tritone is the augmented fourth (A4) or its inversion (the d5) that fits in the scale of the key being played. There is only one tritone in the major scale. In a major scale, this the 4th and 7th notes of the scale or its inversion, the d5 which is played on the 7th and 12th notes.
Of all the intervals, this one wants to resolve the most. It resolves to the nearest chord tone which is half a step away from each note. If it is the A4 in the major scale, it will resolve to the m6. If it is the d5, it will resolve to the M3.
The tritone is how you can define the key, because it will always resolve to the tonic or root note of the scale. (In C Major, the tonic is C. In B Major, the tonic is B, etc). In a major scale, the A4 will resolve to the m6, and the top note of this is the tonic. The d5 in the same scale will resolve to the M3, and the bottom note of this is the tonic.
In a minor scale, it's a little trickier as the tritone resolves to the relative major. The tritone in a natural minor scale is the 2 and 6, and this resolves to the 3 and 5, a M3 which implies the root of the relative major.
Most interval theory is way easier to understand when you hear it in action rather than read about it, so be sure to listen to the examples and reach out in the comments if you have a question.
Intervals are a Pillar of Music
Intervals are an important part of music, as they create the melodies, harmonies, and progressions that make up the musical language. By understanding the quantity and quality of intervals, musicians can better communicate musical ideas with each other as well as create interesting and unique sounds that add texture and depth to their music.