Harmony/The Minor Scale, Modes, & Mode Mixture
The Minor ScaleEdit
Intervals from the tonic: tone, semitone, tone, tone, semitone, tone, tone
The harmonic minor differs in that the 7th is augmented. This turns it into the leading note (in terms of the melodic interval), so this is known as 'sharpenig the leading note'. This means that the interval between the 6th and 7th notes becomes an augmented 2nd.
Intervals from the tonic: tone, semitone, tone, tone, semitone, tone + semitone, semitone
The melodic minor is different going up from going down. Going up, both the 6th and 7th notes are augmented, while going down, they are unaltered (the same as in the natural minor)
When we refer to a modal scale being in its 'natural key', all we mean is that we don't have to use any accidentals when using a blank stave. Some of these keys are used far more often than others. Obviously, Ionian and Aeolian are the main scales used in a modern context. Others, such as the Dorian mode, have seen something of a resurgence in recent years due to pop music. Others, such as the Locrian mode, sound so unusual that they have never really come into fashion despite being possible in theory.
Natural key = C major
Natural key = D dorian
Natural key = E phrygian
Natural key = F lydian
Natural key = G mixolydian
Aeolian (Natural Minor)Edit
Natural key = A natural minor
Natural key = B locrian