A diatonic scale is the name we give to a type of scale that has a very specific formula of intervals between each of the notes. They’re the foundation of western music but it can be confusing exactly what the definition of one is.
In this post we’ll cover what they are, the different types of diatonic scales as well as some of the scales that aren’t diatonic.
What is a diatonic scale?
A diatonic scale is a type of music scale with seven notes (also called a heptonic scale).
Diatonic scales must have two semitone intervals (half steps) and five tone intervals (whole steps) within one octave.
The two semitone intervals should be separated by two and three tones.
If you were to play all the white notes on a piano keyboard, starting on C you would have played a diatonic scale.
Another thing that diatonic scales have in common is that they use all seven pitch letter names (A, B, C, D etc) in sequence without skipping any.
Types of diatonic scale
There isn’t just one diatonic scale, there are lots!
One of the things that makes a diatonic scale is that it has to contain two semitones (half steps) and five tones (whole steps) with the semitones being separated by three tones.
For example you could have, T T S T T T S or T T T S T T S or T S T T S T T.
Let’s look at some of these scales in a bit more detail.
The major scale
The major scale is probably the most familiar and easily recognisable of all diatonic scales.
If you were to play all the white notes on a piano keyboard starting on C you’ll not only play a major scale but a diatonic scale.
The sequence of tones and semitones in a major scale is T T S T T T S.
Hopefully you also notice that the semitones (half steps) are separated by two and three tones (whole steps).
This is how you know it’s a diatonic scale.
You can then transpose this sequence to start on any note and as long as you keep the order of semitones and tones the same, you’ll have played a major scale which is a diatonic scale.
The natural minor scale
Every major scale has a related minor scale.
Relative major and minor scales share exactly the same notes but they start on different pitches.
This means that they have a different sequence of tones and semitones but the distance between the semitones will still be three tones.
For example, the relative minor scale of C major is A natural minor which has the following formula of tones and semitones: T S T T S T T
The modes
The musical modes are a series of scales that are based on the major scale but each have different characteristics.
Each mode starts on a different degree of the major scale.
- Ionian mode – 1st degree
- Dorian mode – 2nd degree
- Phrygian mode – 3rd degree
- Lydian mode – 4th degree
- Mixolydian mode – 5th degree
- Aeolian mode – 6th degree
- Locrian mode – 7th degree
Even though each mode starts on a different note of the scale and has a different tonic note, they are still all diatonic scales but the sequence of semitones and tones is shifted.
The image below of the order of whole and half steps for each mode, shows that the sequence remains the same, but, it shifts by one for each mode.
To read more about modes and how we use them check out our guide to modes in music here but here is a table of the seven modes with what degree of the scale they are, the interval sequence and an example of what notes that would be.
| Mode | Degree | Interval Sequence | Example |
| Ionian | I | T T S T T T S | C D E F G A B C |
| Dorian | II | T S T T T S T | D E F G A B C D |
| Phrygian | III | S T T T S T T | E F G A B C D E |
| Lydian | IV | T T T S T T S | F G A B C D E F |
| Mixolydian | V | T T S T T S T | G A B C D E F G |
| Aeolian | VI | T S T T S T T | A B C D E F G A |
| Locrian | VII | S T T S T T T | B C D E F G A B |
Non diatonic scales
When it comes to the definition of a diatonic scale, there are two camps.
The purists say that it has to have seven notes and have two half steps and five whole step intervals.
The other view, which is more broad, is that a diatonic scale is one that is in a ‘key’.
This is a more literal definition as the word ‘dia’ comes from the greek for ‘through’ or ‘across’ and ‘tonic’ means key.
With that definition, a harmonic minor scale could be classed as a diatonic scale even though it has an augmented 2nd interval.
But, for this post I’ll be going with the first definition.
With that in mind, some non diatonic scales include:
- Harmonic minor scale – As they don’t have two semitones and five tones
- Chromatic scales – As they have more than seven notes all of which are semitones apart
- Whole tone scales – As they have six notes all of which are tones apart
- Pentatonic scales – As they have five notes with no semitone intervals
There are lots of other types of scales but these are some of the most common ones in western music.
Conclusion
I hope that helps make a bit more sense of what is, and what isn’t, a diatonic scale.
If you have any questions that haven’t been covered in this post, just comment below.
