Why is a major second not called a perfect second? [duplicate]

Question

Apart from a second, intervals can be described as either {Diminished, Perfect, Augmented} or {Dim, Minor, Major, Aug} depending on whether or not the major and minor scale share that interval. For example, both the major and minor scale contain a perfect fifth yet they do not share a major/minor 3rd or 6th. This is true for all intervals except for the second. Both the major and minor scale have a major second, so why is it not called a perfect second? I think this would make more sense when learning why certain intervals are be perfect and not major/minor and it also makes more sense when listening to intervals as a minor second interval has the same sort of dissonance that a diminished 5th does so calling it a diminished second could make more sense.

In summary, why are seconds called minor/major?

Answer 1

The minor intervals are not minor because they are found in the minor scale and the same goes for major intervals. The intervals are concepts based on the distance between two notes based on letter name and absolute distance in semitones.

It should also be noted that the term major and minor is used a lot in music and when applied to interval major means further in distance and minor means smaller. In some ways, you can view a minor interval as a half step or semitone above the previous interval set and a major interval as a whole step or tone above the previous interval.

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To better explain why the intervals ended up this way, let's look at this solely from a distance perspective at first. The distances from unison to octave are as follows in semitones:

 0 - 1 - 2 - 3 - 4 - 5 - 6 - 7 - 8 - 9 - 10 - 11 - 12

In C these notes would map to:

 C - D♭  - D - E♭  - E - F - F♯/G♭  - G - A♭ - A - B♭  - B  - C 

As you can see, both 0 and 12 map to C and the furthest you could be away from a C in semitones is 6. This leaves us with 5 notes on each side with 1 - 2 - 3 - 4 - 5 closer to 0 and 7 - 8 - 9 - 10 - 11 closer to 12.

Now let's look at the standard interval names. In this I will use M for major, m for minor, P for Perfect and tt for tritone (which is considered both an Augmented 4th and a diminished 5th).

 P1 - m2 - M2 - m3 - M3 - P4 - tt - P5 - m6 - M6 - m7 - M7 - P8

Now looking at the whole interval spectrum, we notice

• The tritone (or 6 semitones away) has a perfect interval above and below (P4 - tt - P5) and can be described as both an A4 and d5 for this reason.
• The note you are basing the name off of (C in this case which is both 0 and 12) is also perfect (P1 for unison P8 for octave) .
• The other notes are group into twos (because of the two semitones typical max in scales) with the smaller one being minor and the bigger one being major (m2 - M2 - m3 - M3) and (m6 - M6 - m7 - M7).
• The augmented and diminished intervals of the major and minor intervals are for when one of the intervals stretches out of its typical designation.

So in short, a major interval just means it's the bigger of a set of two possible intervals. The fact that the minor scale uses it is kind of irrelevant in this naming scheme.

Answer 2

Perfect intervals are called that because there is a purity to there sound that is not present in the other intervals. Second intervals have a distinct dissonant quality to them that is really very different to the perfect intervals.

This idea is most evident when you hear a modulation pedal in effect. Listen to the seconds it has a distinct uneasy quality to it where the fifths and the octaves sound much less dissonant.

Take a look at this video it illustrate it well.

Answer 3

Music theory is an evaluation. The ratio (the nomenclature of the intervals) were developed by Pythagoras when he compared the note played by one string to another note played by the same string but divided into a smaller section. Perfect intervals only include the unison/octave, fifth, and fourth. That is due to the ratio of the string length. Their respective ratios are 2/1, 3/2, 4/3, which are fairly simple, so they are considered perfect. On the other hand, a complicated and therefore dissonant ratio is less likely to be called perfect.