Intervals are the building blocks of music. Whether they are vertical (chords) or horizontal (melody), the ability to recognize intervals is a valuable skill for anyone wanting to become a better sightreader, composer or improviser.
The octave is the point at which the seven notes in a scale start to repeat themselves. E.g., if you start on a “c,” the next highest (or lowest) “c” is an octave away. The note that is five pitches away is called a fifth.
A fifth in its purest form is perfect; this is the interval that the strings on most bowed string instruments are tuned. (A bass is tuned in perfect 4ths, which is the inversion of a perfect fifth). Therefore, a perfect fifth + a perfect fourth = an octave. How can this be when 4+5 = 9?! It’s because the intervals are always measured inclusively of their start and end points. Fifths, even more than fourths, are the gold standard when defining what key you are in.
Other intervals, (seconds, thirds, sixths and sevenths) cannot be perfect; only either major or minor. A third is a special interval in that it is the interval that defines whether a tonality is major or minor. A blue-note is a third that cannot decide whether it is major or minor; jazz could not exist without this vacillation. The inverse of a third is a sixth. Seconds, and their partners sevenths, are intervals that serve in a vertical sense to liven up a chord by making it a little “dirtier.” A major seventh or minor second is the dirtiest interval of all.
While dirty can also describe the tritone, a better word for it is shifty. A tritone is the interval between a fifth and a fourth, or exactly halfway between 2 notes an octave apart. Technically, it is called either an augmented fourth or a diminished fifth, depending on how it is spelled. It is a chameleon interval which is unstable and wants to resolve, but it can resolve outward (to a sixth) or inward (to a third). Movie music that is used to accompany dirty dealings, cliffhanging, mystery and shock is heavy with tritones, some of which are there for their own sake and aren’t about to give you the satisfaction of a resolution.
Here are some easily recognizable intervals that occur in everyday living and in standard music repertoire.
Für Elise by Beethoven starts with a minor 2nd, wavering up high in the right hand. (Insert viola joke here). The first six notes of “Chopsticks” are a major second apart, played simultaneously.
Pick up a phone (landline). You hear that dial tone? That’s a major third. Now drive very slowly in the left lane on I-40. You hear that car horn? A lot of 2-tone horns use this interval also.
Mozart’s Eine Kleine Nachtmusik is one of the most instantly recognizable tunes ever written. The first two notes are a fourth apart.
Strauss’ Also Sprach Zarathustra starts with two perfect intervals in a row a fifth and then a fourth. This interval is also all over the opening of Beethoven’s Symphony N. 9, vertically in the bed of 16th notes laid down by the lower strings, and horizontally in the violin melody.
Still confused? Listen and learn.