In Western tonal Music, the concept of scale, key, and mode form the structural basis of pitch organisation. In this article, we will explore the difference between these terms and use practical examples to make each concept easy to understand.
What is a Scale?
A scale is a sequence of musical pitches arranged within one octave. We’ll dive into this in more detail below. For now, let’s just stick with simple definition!
Understanding the Octave
On the piano, each octave contains 12 semitones (the full set of white and black keys). However, Western music uses 7 notes names (A-G), which repeat every octave. This means one octave spans 12 semitones but we name only 7 notes (heptatonic scale). The 8th note is the same as the first note, but one octave higher!
The tonic (also called root note or key note) is the first note and acts as the home base of the scale.
So these 12 semitones are grouped into patterns of whole steps (2 half steps) and half steps, depending on the mode of the scale.
What is a Mode?
A mode is the interval pattern (whole steps & half steps) between the notes of a scale. It creates the scale’s sound, colour, and character. Mode is the identity of the scale. Modes come from the ancient Greek system. Traditional modal theory uses only the natural keys (white keys on the piano).
There are 7 diatonic modes based on the 7 natural starting notes (starting and ending on a different scale degree) of the parent scale (usually major). So use the same notes as the parent major, but there is a different tonal center.
Ionian (C-D-E-F-G-A-B-C),
Dorian (D-E-F-G-A-B-C-D),
Phrygian (E-F-G-A-B-C-D-E),
Lydian (F-G-A-B-C-D-E-F),
Mixolydian (G-A-B-C-D-E-F-G),
Aeolian (A-B-C-D-E-F-G-A),
Locrian (B-C-D-E-F-G-A-B), each with its own interval formula and sonic identity.
The two most familiar modes in Western music are:
Ionian Mode (Major Scale): T-T-S-T-T-T-S & Aeolian Mode (Natural Minor Scale): T-S-T-T-S-T-T
Changing only the tonic note while keeping the same mode keeps the musical character the same – only the pitch range changes!
So, a scale is the combination of A. key note/ tonic & B. a mode (interval pattern). Is simply a structures selection of pitches within an octave.
Example:
- C major = root C + Ionian mode
- A natural minor = root A + Aeolian mode
This naming structure tells us exactly which scale we’re dealing with.
Introduction to the Western Tonal Music System
At the beginning of the 17th century, the tonal music system of major and minor modes, as we know them today, was formed. Specifically, an octave is a division of 7 unequal parts, consisting of whole tones and semitones. We call this division the diatonic genus. In contrast, the division of the octave into 12 parts is called the chromatic genus.
Note: The term genus (genos (γένος in Greek), comes from ancient music theory. It refers to a “family” or “class” of scales, categorised by hoe the notes are spaced within a specific interval.
The chromatic genus has only one form. The diatonic genus has two forms. Each form depending on the sequence of tones and semitones, we call it a mode.
In other words, a mode is a division of the octave with a specific sequence of whole tones (T) and semitones (S). In Western music, the primary modes are Major and Minor.
Each mode is just a theoretical approach. When we apply this specific sequence of tones and semitones to a series of notes starting from a specific pitch, it becomes a practical application called a scale (σκάλα ή κλίμακα).
The scale takes its name from the first note (the tonic) followed by the mode, from example C Major.
What is a Diatonic Scale
For a scale to be classified as diatonic, it isn’t enough to just have a sequence of notes. It must follow a specific mathematical and acoustic based on 7 unique pitches.
Characteristics of the Diatonic Scale:
- 7 Unique Notes: It consists of seven different pitches in succession ( C, D, E, F, G, A, B)
- 5 Tones and 2 Semitones: Its internal structure includes five Tones and Two Semitones
- The Spacing of Semitones: Two semitones are never adjacent. They must always be separated by at least two or three tones.
Key Signature and Accidentals
A diatonic scale is defined by its key signature at the beginning of the staff (the sharps or flats that apply to the entire piece).
The Distinction: In purely diatonic scales (Major and Natural Minor), we only use the notes specified by the key signature.
Why Harmonic and Melodic scales are not Diatonic: Because they introduce “foreign” accidentals (like the raised leading tone) that alter the natural intervals. So the harmonic minor contains an interval of 1,5 tones (augmented second), which “breaks” the diatonic succession.
The Pentatonic Scale
Every culture developed its own music and its own unique musical language, which evolved over time. By studying different eras in music history, we see various musical idioms and ways of writing music that took many centuries to reach their final form.
One of the oldest musical systems (the relationships between notes) is the pentatonic scale. This consists of five unequal parts: three whole tones and two minor thirds. Many civilizations used this five-note system. If we add a note between each minor third, we create the heptatonic (seven-note) system.
As I mentioned earlier, our modern seven-note system was created by dividing the octave into 12 equal parts (equal division of intervals). This came from the temperament of notes according to their frequencies.
The pentatonic scale is a subset of the diatonic, but with one key difference: it consists of 5 notes instead of 7. Although it borrows its notes from the diatonic system, the pentatonic scale to be “diatonic” in the strict, as it lacks semitones.
How is is derived from the Diatonic?
Pentatonic scales are created by removing the degrees that cause “friction” (the semitones).
Major Pentatonic: Derived from the Major Diatonic by removing the 4th and 7th degrees (in C: C-D-E-G-A).
Minor Pentatonic: Derived from the Natural Minor by removing the 2nd and 6th degrees (in Am: A-C-D-E-G).
Due to the absence of semitones, pentatonic scales have an “open” and harmomious character. Any note played sounds consistently correct the accompaniment, making it the ideal tool for improvisation in Blues, Rock, and Jazz.
So, is a pentatonic scale diatonic?
Answer: No. A diatonic scale must have 7 unique notes and a specific sequence of 5 Tonic and 2 Semitones.
Diatonic: T – T – S – T – T – T – S
Major Pentatonic: T – T – T+S (minor third) – T – T+S
Minor Pentatonic: T+S – T – T – T+S – T
Pentatonic -> no semitones
Hexatonic Scales
A Hexatonic scale contains 6 unique notes per octave.
- The Whole Tone Scale has a structure of: T-T-T-T-T-T, and it lacks a tonal center. (C-D-E-F#-G#-A#). (Debussy)
- The Blues Scales (the most popular hexatonic scales), with structure: minor pentatonic+ Blue Note (diminished 5th). A-C-D-D#-E-G
- The Augmented Scale (often used in Jazz). Structure: Alternating Minor 3rd and Half Step. C-Eb-E-G-Ab-B
Building a Scale on Any Note
Once you know the mode’s pattern, you can build that scale starting from any tonic note.
For example: E Major
Start on E, the follow the pattern of Ionian Mode – the major pattern: T-T-S-T-T-T-S
Starting from E (tonic)
Even though E major uses sharps and C major does not, the musical character is identical — only the starting pitch changes.
Diatonic is the System (Genus): It defines a specific structure of 7 unique pitches made of 5 Tones and 2 Semitones.
Mode is the Arrangement: It tells us which note of the 7-note set we start and end on. (A specific way of starting and ending a scale within the Diatonic system)
Major and Minor are the two primary Types (Modes) of the Diatonic system we use in modern music. Furthermore, we can “find” these two modes in Modern Western music, because they provide sense of a “home” note (the Tonic).
Scales vs Keys
A key creates the “tonal environment”. When a piece of music uses the notes of a scale, highlights the tonic and builds harmony based on that scale’s pattern but keeps the mode’s character.
So a key is not a scale itself – it’s the musical environment that uses the scale. Scales define the sound of a key.
For example: A piece in E major, uses the notes of the E Major scale, emphasizes E as the tonal center and uses harmony consistent with that mode.
How Tonality Works
Our sense of key or tonality comes from:
- The tonic is emphasized in melodies and endings. So the tonic is the pitch from which the scale is generated and to which tonal music tends to resolve.
- The interval pattern of the mode creates tension and release.
- The scale degrees (1-7) each have a role in the mode’s character.
For example, when we say “This sonata is composed in E-flat major,” we mean that the piece is written in the key of E-flat major, meaning its melodies and harmonies are based on the E-flat major scale.
Changing the tonic while keeping the same mode keeps the same sound, just higher or lower.
Step-by-step Built-Up of A Scale
- First we’ll choose a mode. Decide if you want Major/Ionian or Minor/Aeolian.
- Then select a Key-Note. The first note of the scale-The tonic.
- Apply the interval pattern – Follow the Tone – Semitone Pattern of the chosen mode.