At some places it is said to only comprise of white keys. At other places it is written that it is any scale with the composition of either major or minor scales (consisting of whole and semitones) even if including the black keys. Which one is it?
Diatonic means belonging to the key. Those other notes are called chromatic. So, in a way, it's right. All the white keys on a piano are diatonic. But only to the keys of C major and A natural minor. They certainly won't be diatonic to, say, C♯ major!
Since there are twelve available keys in 12tet, then there are 12 different diatonic sets of notes. But please read on...
Major, natural, harmonic and melodic minor scale notes are all deemed to be diatonic - which is basically scales made up from tones and semitones (and in harmonic minor's case, a tone-and-a-half) intervals between notes. Although some musos prefer to have only the major keys containing diatonic notes.
So, yes, all the black keys can come out to play diatonically - provided they feature in the key signature in the piece. All other notes (which ironically include some white keys in some keys) are deemed to be chromatic.
At some places it is said [a diatonic scale is comprised only] of white keys...
Obviously that is a reference to the piano keyboard. But we can play diatonic scales on other instruments. So defining "diatonic" in that way is not a very good definition. We need to know what diatonic means in musical terms rather than keyboard shape.
...it is any scale with the composition of either major...
A diatonic scale includes 7 tones repeated at the octave.
Two ways to generate the pattern of 7 tones are:
- a series of whole-tones (WT) and half-tones (HT)
- a series of ascending perfect fifths (↑P5)
To demonstrate those two methods to produce the diatonic scale
C D E F G A B (C)...
C (↑WT) D (↑WT) E (↑HT) F (↑WT) G (↑WT) A (↑WT) B (↑HT) C
F (↑P5) C (↑P5) G (↑P5) D (↑P5) A (↑P5) E (↑P5) B
Two additional points to keep in mind...
- the pattern is transposable, you can start the series on any pitch, ex.
Eb F G Ab Bb C D Ebor going in ascending fifths
Ab Eb Bb F C G D
- you take any 'rotation' or permutation of a diatonic scale and get various specific scales, ex.
Eb F G Ab Bb C D Ebis a major scale,
F G Ab Bb C D Eb Fis the Dorian mode,
C D Eb F G Ab Bb Cis the natural minor scale, etc.
So "diatonic" is defined by the pattern of steps (intervals) and the diatonic tones can be permuted and transposed.
The word "diatonic" literally means "through the tones".
In the strictest sense, this means any scale that has an interval pattern identical to just the white keys: five whole steps and two half steps, with the half steps separated by a perfect fifth. All major scales, and all of their related modes, are diatonic. (This is sometimes defined in other ways - the Harvard Dictionary of Music says it's a heptatonic scale composed of pitches that are adjacent to each other in the circle of fifths, which gets you the same result.)
In the loosest sense it means any heptatonic (7 note) scale that has exactly one of each letter. This expands the definition to include the harmonic and melodic minor scales and their related modes.
There's also an "in between" interpretation that considers diatonic scales to be those which have one of each letter, and are composed only of whole steps and half steps. This definition includes the melodic minor scales and related modes, but not the harmonic minors, because they include an augmented second interval.
If you play only white keys you get a diatonic scale, but under any definition it is not the only diatonic scale.
Virtually all music theory texts use the strictest interpretation.
Let's have a look at these two sentences:
At some places it is said to only comprise of white keys
You've talked about "it", implying that there's one diatonic scale.
Modern musical keyboards are designed so that the white notes form a diatonic scale
Here, you've said "a diatonic scale", implying there's more than one.
So which is true?
Actually "diatonic scale" can be used in both senses.
We can talk about "the diatonic scale", meaning the pattern of intervals.
Or we can talk about diatonic scales - i.e. all scales that follow the diatonic pattern, starting from any note in the chromatic scale, and any starting point in the diatonic pattern.
So while diatonic scales can include both white and black notes, it's also true that the white notes on a piano do completely express the diatonic pattern of intervals - i.e. the diatonic scale (although one can define the scale in other ways)
Something is diatonic (to a major scale, which is what we're talking about here) when it contains only the notes of a major scale. This can apply to chords, scales/modes, melodies, a whole song, et cetera, but in this case you mean that the scale only uses notes from a major scale (note that it could be minor, or even modal, since those are all diatonic to the major scale). That means a couple of things:
- There will be no accidentals, since everything should be covered in the key signature
- If you transposed it to C major (or whatever relative mode of C), it would only use the white notes.
BIG "if". Music in A major uses three black keys, but it's still diatonic. Only diatonic music in C major follows this pattern.
All the white notes are diatonic, but not all the diatonic stuff uses just the white notes.