Musical Intervals in Musical DiscoveryThe screen shot below is at the advanced level, explaining the interval of a major 3rd. At early grades the screen is less cluttered and easy for beginners to understand.
Major Third
This is the interval between the first and third notes of the major scale, the tonic and the mediant. It consists of 4 semitones. There are also major thirds between the fourth and sixth notes of the major scale, and between the fifth and seventh notes.
It is a sweet, bright, and harmonious interval, as it is one of the essential ingredients of the major triad. The other ingredient in the triad, apart from the tonic, is the perfect fifth, or dominant, which has a bare, open sound when played with the tonic only. Adding in the major third or mediant, makes the chord sound rich and full. When inverted, it becomes a minor sixth.
Examples:
| Interval between | ||
| First Note | Second Note | Line of song |
| Dump- | -ty | Hump-ty dump-ty sat on a wall. |
| Wat- | -er | Jack and Jill went up a hill to fetch a pail of wat-er. |
In the history of polyphonic music, early church music was all sung in unison at first, then octaves were permitted in order to allow men and boys or women to sing together. Later, perfect fifths were permitted, as these still sounded "pure" and "holy" to the ears of the church authorities. But major thirds were completely banned, as they sounded un-holy, even "lascivious".
Looking at the science behind music, an interval sounds pleasant and harmonious if the ratio of the frequencies is a simple one, like 1:2, 2:3, 3:4 or 4:5. The mediant's frequency has a ratio of 5/4 to the tonic. This is equivalent to dividing a string into 5 parts, then bring the note down 2 octaves. The frequencies of the 3 notes of the major triad are in the ratio 4:5:6 to each other.
When a string vibrates, the loudest note is what we hear, called the fundamental. But the string also vibrates in sub-sections, such as halves, thirds, quarters and fifths, sounding fainter notes called harmonics or overtones. The relative strengths of the different overtones define the quality or "timbre" of the sound. The most harmonious intervals are those which form part of the natural overtones of the root note. The major third corresponds to the overtone from a string vibrating in 5 equal sections, and this is the 4th strongest overtone. So playing a major third reinforces this natural overtone of the root, instead of clashing with it.