Interval Names
By looking at the chromatic scale you can see why it is necessary to have very specific names for intervals. C to D is an interval of a second, but so is C to Db. C and D are a tone apart while C and Db are a semitone apart.
A semitone is known as an interval of a minor second, while a tone is called a major second. Most intervals have at least two possible variations. One example which relates directly to chords is the interval of a third. C to E is called a major third (4 semitones apart) while C to Eb is called a minor third (3 semitones apart).
It is the letter names involved which determines the fact that both intervals are called (C D E = 1 2 3). If you count third intervals up from the note D, D to F is a minor third, while D to F# is a major third and so on. Most chords are constructed by stacking various major and minor third intervals one on top of the other.
There are many other intervals which are variations on all possible numbers up to an octave (2nds, 3rds, 4ths, 5ths, 6ths and 7ths) but for now we will concentrate on thirds because of their importance in building and understanding chords. For more information on intervals see Progressive Theory .
