Piano World Home Page Forums Our Most Popular Forums Adult Beginners Forum Simple (?) music theory question.

I am now trying to figure out suspended chords and I noticed that some notes are referred to as "Major" and some are "Perfect". For example in the C major scale D is a major 2nd but F is a perfect 4th. Why is that and what does it mean?

Check out:
https://en.m.wikipedia.org/wiki/Interval_(music)

In Western music there are twelve intervals within the range of an octave. Only four of them are called "perfect" (unison, fourth, fifth, octave) because the ratios of the frequencies of the two notes are simple fractions which causes them to sound pleasing to the ear. All the other intervals have a major and a minor version. The major scale only uses some of these intervals and the minor scale uses others.

I think this might be a bit misleading. Every major scale has every interval from m2 to M7, but it depends on where you start the interval.

The quoted link gives a lot of different information, so it is hard to know what in particular you find to be misleading.

But I'll hazard a guess since you referred to major scales in particular.

The naming of intervals has been derived from major scales, always from the tonic up. Thus:
C to same C = P unison
CD = M2
CE = M3
CF = P4
CG = P5
CA = M6
CB = M7
C to next highest C = P8

They are all majors unless they are perfects. These also give us the measure of how many semitones they are apart - you could consider semitones to be sort of like "inches", like a smallest unit of measure.
Any interval that is a semitone smaller than these majors will be minors; two semitones smaller = diminished; one semitone higher = augmented. With the perfects you can have a diminished or augmented. The reason is historical.

Yes, you can have a minor interval within a major key. DF involves two notes that exist in the key of C major, and DF is m3 (minor 3). But if you use the system of considering the bottom note to be the tonic in order to name the interval, in D major the higher note is F#, DF# = M3, a semitone lower DF = m3, so the system still holds true. It's probably easier to know how many semitones = m3 (three) or M4 (four) and go by that. Or sound, if you know what a major 3rd or minor 3rd sounds like.

When you take a major 2nd, invert it, you get a minor 7th. If you take a major 3rd, invert it, you will have a minor 6th. Not so straight forward.

However, invert a perfect fifth, you get a perfect forth. Invert a perfect fourth, you get back a perfect fifth. Isn't that just perfect?