Intervals, scales and key signatures: WACE Year 12 Music
“Identify, construct and notate intervals, major and minor scales, modes and their key signatures as part of music literacy”
An interval is the distance between two pitches, named by a number (size) and a quality (perfect, major, minor, augmented or diminished); scales are ordered patterns of tones and semitones, with major scales following T T S T T T S and the three minor forms altering the sixth and seventh; key signatures place sharps or flats in the fixed order given by the circle of fifths so the music plays in the correct key.
What this dot point is asking
SCSA wants you to read, build and write the basic raw material of tonal music quickly and without error. In the aural and theory paper these skills underpin dictation, harmony and analysis, so they need to be automatic rather than worked out from scratch each time.
Intervals
An interval has two parts: a size (a number) and a quality (a word).
The size is found by counting letter names inclusively from the lower to the upper note. From C up to G is a fifth (C, D, E, F, G is five letters). The size ignores sharps and flats; only the letter names are counted.
The quality describes the exact distance in semitones:
- Unisons, fourths, fifths and octaves can be perfect, augmented or diminished.
- Seconds, thirds, sixths and sevenths can be major, minor, augmented or diminished.
A major interval made one semitone smaller becomes minor; a minor made one smaller becomes diminished. A perfect or major made one semitone larger becomes augmented. Worked counting in semitones is the reliable method: a major third is 4 semitones, a perfect fifth is 7, a minor seventh is 10.
Step 1: count letter names for the size
Identify the interval from A up to F. Count letter names inclusively: A, B, C, D, E, F is six letters, so the size is a sixth. The size ignores any sharps or flats.
Step 2: count semitones for the quality
A to F is 8 semitones. A major sixth is 9 semitones, so 8 semitones is one smaller: a minor sixth.
Step 3: state the full label
Combine size and quality: the interval is a minor sixth. Always give both parts, because a bare "sixth" earns half marks at most.
Major and minor scales
A major scale follows the fixed tone and semitone pattern T T S T T T S. Starting on C this gives C D E F G A B C with no sharps or flats. Starting on any other note, accidentals are added to keep that exact pattern.
Minor scales come in three forms built on the same key signature as their relative minor:
- Natural minor uses the key signature unchanged (pattern T S T T S T T).
- Harmonic minor raises the seventh degree by a semitone, creating the leading note and the distinctive augmented second between the sixth and seventh.
- Melodic minor raises both the sixth and seventh ascending, then lowers both to the natural form descending.
The relative minor of a major key starts on the sixth degree of that major scale; A minor is the relative minor of C major. The parallel minor shares the same tonic but a different key signature; C minor is the parallel minor of C major.
Modes
Modes are scales built on each degree of the major scale using the same notes but a different starting pitch. The white-note modes are a quick reference: Ionian (C, the major scale), Dorian (D), Phrygian (E), Lydian (F), Mixolydian (G), Aeolian (A, the natural minor) and Locrian (B). Modes appear often in jazz and contemporary contexts, so recognising Dorian and Mixolydian by ear and on the page is worth practising.
Key signatures and the circle of fifths
A key signature is the group of sharps or flats written after the clef that applies for the whole piece. They are written in a fixed order:
- Sharps: F C G D A E B.
- Flats: B E A D G C F (the reverse).
The circle of fifths organises keys by adding one sharp for each step clockwise (a fifth up) and one flat for each step anticlockwise (a fourth up). C has none, G has one sharp, D has two, and so on. To name a sharp key, the last sharp is the leading note, so the key is a semitone above it. To name a flat key, the second-last flat names the key.
For sharp keys, go a semitone above the last sharp to find the major key. For flat keys, the second-to-last flat is the name of the major key. F major (one flat) is the exception worth memorising directly.
Why this matters for the exam
Dictation, harmonic analysis and composition all assume you can move between a key signature, its scale and the intervals within it instantly. A student who has to derive the pattern each time loses marks to time pressure and small slips. The fix is drilling: write every key signature and scale from memory until they are reflexes, then test recognition by ear.
- Counting interval size from the wrong note or exclusively
- Always count letter names inclusively from the lower note, including both ends.
- Forgetting that interval size ignores accidentals
- C to G sharp is still a fifth (augmented), not a sixth.
- Mixing up the three minor forms
- Harmonic raises only the seventh; melodic raises the sixth and seventh ascending and reverts descending.
- Writing key signature accidentals out of order
- Sharps and flats must follow F C G D A E B and its reverse, in the correct stave positions.
Exam-style questions
Questions in the style of SCSA exam questions on this dot point, each with a worked answer. They are written by ExamExplained unless tagged "Past paper"; the year shows the paper a question is modelled on.
WACE 2022-style8 marksFrom the printed melody, identify the four labelled intervals (a) to (d) by size and quality, and state the key of the excerpt, justifying your answer from the key signature and final note.Show worked answer →
Work each interval in two steps: count letter names inclusively for the size, then count semitones for the quality.
Example for one interval: from D up to B flat is six letter names (D E F G A B) so a sixth; D to B flat is 8 semitones, and a major sixth is 9 semitones, so this is a minor sixth.
Markers want both parts right: a bare "sixth" with no quality earns half marks at most.
For the key, name the key signature first ( = B flat and E flat suggests B flat major or G minor), then use the final note and any raised leading note. If the melody ends on G and an F sharp appears, it is G minor (harmonic), not B flat major.
State the evidence explicitly: "two flats plus an F sharp and a final G indicate G harmonic minor." Examiners reward the justification, not just the answer.
WACE 2021-style6 marksNotate, using accidentals rather than a key signature, an ascending E harmonic minor scale and a descending D melodic minor scale. Then explain the interval that gives the harmonic minor its distinctive character.Show worked answer →
E harmonic minor ascending: E F sharp G A B C D sharp E. The seventh degree (D) is raised to D sharp to form the leading note; the rest follows the natural minor.
D melodic minor descending: D C natural B flat A G F E D. Descending, the raised sixth and seventh revert to the natural minor form, so C and B return to naturals/flats.
Distinctive interval: between the lowered sixth (C in E minor) and the raised seventh (D sharp) lies an augmented second of 3 semitones, to . This gap gives harmonic minor its exotic, tense colour.
Common loss of marks: forgetting that melodic minor changes shape between ascending and descending, or writing the augmented second as a minor third by spelling it C to E flat instead of C to D sharp. Spelling matters: the size must be a second.