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2. Score Reading: Describing Chords and Prevailing Key


Grade 8 Music Theory - Describing Chords & Prevailing Key

In most ABRSM Grade 8 Music Theory exam papers, you will be asked to find or describe chords within a score. Chords usually need to be described in full, with their name, position and prevailing key. Typically answers can be written as follows:

  • Using the Roman numeral system
  • Using the letters a, b, c or d to show position/inversion
  • Using abbreviations for chromatic chords, such as “dim.”, “N6”, “Ger 6” etc.

When you are asked to describe a chord, the notes you need to include will be marked either with an asterisk, or with a bracket.

An asterisk is used when all the notes line up vertically, and a bracket or box is used when some or all of the chord notes do not sound simultaneously.

In the first example here, the chord to describe contains all the notes directly under the asterisk: G-D-E-G in the left hand, and Bb-D-E-Bb in the right hand.

chord with asterisk grade 8 music theory

In the second example, the box shows that the chord is made up of the notes in the right hand beginning on C# and followed by E-G-A-C#-E-G, and also the left hand notes of the minim (half note) A and crotchet (quarter note) E (which are still sounding at this point), followed by C#-E-G-A.

chord with box grade 8 music theory


To work out a chord successfully, use this three-step process.

1. Work out the chord’s name e.g. G7

2. Work out its inversion e.g. G7b

3. Work out the prevailing key e.g. G7b in C minor


Each step is described in detail below.


Describing Chords by Name

Write out the names of all the notes encompassed by the asterisk or boxed area, and then stack them in thirds. Discard any duplicates.

For example, in [A] above, the notes stacked in thirds and with duplicates removed are E-G-Bb-D. In [B], the notes are A-C#-E-G.

The lowest note is the root of the chord, and gives the chord its letter name. The quality (major, minor, augmented or diminished) of the chord depends on the intervals of the next two notes, relative to the root.

  • Major third + perfect 5th = Major chord (e.g. C-E-G). Use capital letters (e.g. IV).
  • Minor third + perfect 5th = Minor chord (e.g. C-Eb-G). Use lower case letters (e.g. iv).
  • Major third + augmented 5th = Augmented chord (e.g. C-E-G#). Use capitals and a plus sign (e.g. IV+)
  • Minor third + diminished 5th = Diminished chord (e.g. C-Eb-Gb). Use lower case letters and a ° symbol (e.g. iv°)


Don’t forget to check:

  • The key signature
  • Whether any accidentals written earlier in the bar still apply
  • Whether there has been a sneaky change of clef earlier in the bar or stave


The basic 3-note triads, e.g. C major or Bb minor, should be easy enough to work out. 

Four- or five-note chords may take a bit more detective work:


1. Added 7th chords are a triad plus the 7th above the root, e.g. G-B-D-F.

2. Diminished 7th chords are vii° or ii° plus the diminished 7th above the root, e.g. B-D-F-Ab.

3. Neapolitan 6th chords are bII – in other words they are built on a flattened supertonic (2nd degree of the scale). If the key is C minor and the chord notes are Db-F-Ab, you have found a Neapolitan 6th chord (you can write it as “N6”).

4. The group of chords called the “augmented 6ths” is made up of the “Italian”, “French” and “German” 6ths. These are perhaps some of the more confusing chords to differentiate – so here are some tips!

  • All augmented 6th chords contain a tonic note. So, if the prevailing key is C major, they will contain the note C.
  • The “augmented 6th” part of the chord is formed by adding the note a major third below the tonic (Ab) plus an augmented 4th above (F#). Together, these two notes make the interval of an augmented 6th. You can also commit to memory that neither of these notes are found in the prevailing key – they are what makes the chord chromatic.
  • The Italian 6th is nothing more than these three notes e.g. Ab-C-F#.
  • The French 6th adds the note a tone higher than the tonic: Ab-C-D-F#. This produces a chord which has a “whole tone” feel to it and thus sounds rather dreamy and is preferred by French composers such as Debussy.
  • The German 6th adds the note a minor 3rd higher than the tonic: Ab-C-Eb-F#. (This chord is an enharmonic dominant 7th - this particular chord could be spelled as Ab-C-Eb-Gb, for example, to make V7 in Db major.)
  • If you stack an augmented 6th chord in thirds, you will find that there is a diminished 3rd in it somewhere (e.g. F#-Ab). So, the presence of a diminished 3rd should quickly alert you to the fact that you are dealing with an augmented 6th chord (an augmented 6th is an inverted diminished 3rd).
  • A trick to remembering the names of the augmented 6th chords is to think of them geographically. Italy is furthest south, and is the simple 3-note version. Moving northwards to France, you add a note “north” of the tonic. Finally, moving further northwards to Germany, you add the note even further from the tonic.

5. Some chords will not stack in thirds and may appear at first glance to be nothing more than a random collection of notes. In almost every case, these will in fact be extended dominant chords, and you can verify this by checking the next chord, which should be the tonic chord.

An extended dominant chord will always contain a root (i.e. the dominant note in the prevailing key). The other notes it contains can vary! The following examples are based on C major:

  • V7 (G-B-D-F) should be familiar to you.
  • V9 (G-B-D-A) contains three consecutive scale notes, G-A-B, which can clash if played too closely together. The third is often omitted to prevent this.
  • V11 (G-B-D-C) again has a potentially clashing B/C, so the third is sometimes omitted.
  • V13 (G-B-D-E) looks like iii7 (E-G-B-D), so be careful! Remember that the dominant chord has a strong relationship with the tonic, so we would process this chord aurally as V13-I rather than iii7-I.
  • Extended chords can be combined. You may see G-D-F-A for example. When naming an extended dominant chord, only use the number of the added note furthest from the root. In this case, there is an added 7th and 9th, but the chord should be named as “V9”.


Chord Inversions

After you have stacked the chord in thirds, check which note is the lowest sounding one in the chord in the score. Then compare this note with the stacked chord to find the inversion.

  • Root = lowest note > root position (a)
  • Third = lowest note > first inversion (b)
  • Fifth = lowest note > second inversion (c)
  • Seventh = lowest note > third inversion (d)

Watch out! The lowest sounding note in the chord might not be the one written on the lowest stave. For example, in a cello sonata, the cello part will be placed above the piano part, but may well contain lower-pitched notes than the piano part. It is the lowest sounding note which determines the inversion – not the lowest written.


How to Find the Prevailing Key

The key at the start of a piece of music is the “original” key. Music can change key for brief moments, or for extended passages. When a key change occurs but does not settle, we say the music is “passing through” that key – it is on its way somewhere else. When a key change settles for a number of bars – enough to make the new tonic feel established – the music has “modulated”. The “prevailing” key is whatever key the music is in at any particular moment in time, and you need to know the prevailing key before you can describe a chord with Roman numerals.

To work out the prevailing key, use the following clues to help you do some detective work! Take the chord you have stacked in thirds, and work out what type of chord it must be. The type of chord it is will help you understand what the prevailing key is.


1. Is it a Dominant 7th?
Clue: Major chord with minor 7th above root e.g. G-B-D-F
Prevailing key: Perfect 4th above root e.g. C (progression: V7-I)
Check: whether prevailing key is major or minor

2. Is it a Supertonic 7th?
Clue: Minor or diminished chord with minor 7th above root e.g. D-F-A-C (ii7) or B-D-F-A (ii°7).
Prevailing key: Next chord should be V followed by prevailing key tonic chord, or a second inversion tonic chord (progression ii-V-I)
Check: whether prevailing key is major or minor.

3. Is it a Diminished 7th?
Clue: 4-note chord stacked in minor thirds e.g. B-D-F-Ab.
Prevailing key: the dim7 chord will be VII or II . The next chord(s) will normally be V or I-V.
Check: whether prevailing key is major or minor.

4. Is it a Neapolitan 6th?
Clue: Deceptively “simple” 3-note major chord, uses accidentals.
Prevailing key: Next chord should be V in the correct prevailing key, often followed by I. (N6-V-I)
Check: whether the prevailing key is major or minor.

5. Is it an Augmented 6th?
Clue: Diminished 3rd found when chord stacked in thirds.
Prevailing key: Take the augmented 6th interval and move each note out by one semitone so that you find an octave e.g. if you have Ab-F#, move Ab by a semitone to G, and F# by a semitone to G. This is the dominant note in the prevailing key. In this case, the prevailing key is C. (Aug6-V-I)
Check: whether the prevailing key is major or minor.

6. Is it an Extended Dominant?
Clue: chord will not stack in thirds.
Prevailing key: Look at the bass line – you should see a rising 4th (or falling 5th) to the next bass note e.g. G-C. These are chords V-I.
Check: whether the prevailing key is major or minor.


Some Examples of Chords and their Prevailing Keys

Here are some chords which have been extracted from real pieces of music. Try to “solve” the chords yourself using the plan outlined below, then compare your answer to the one on this page.

Plan: Write down chord notes > stack in 3rds (if possible) > name chord and inversion > check progression for prevailing key.


1. From a Chopin Prelude Op.28 no.20

 chopin prelude op 28

• Chord notes: F-B-D-G
• Stack in thirds: G-B-D-F
• Chord: G7 = V7d
• Key: C minor (next chord is C-Eb-G)


2. From “La Fille aux Cheveux de Lin” by Debussy

debussy fille aux cheveux 


• Chord notes: Gb-Cb-Fb-Ab-Cb-Db-Fb-Ab-Cb-Db-Fb-Ab (don’t forget the dotted minims (dotted half notes) which are still sounding from the first beat of the bar). Remove duplicates: Gb-Cb-Fb-Ab-Db
• Stack in thirds: Not possible > presume it’s an extended dominant > check bass line > Gb (V)-Cb (I)
• Chord: Gb major extended. Triad: Gb-(Bb omitted)-Db; 7th=Fb; 9th=Ab; 11th=Cb > Chord is V11a
• Key: Cb major (nice!)


3. From Chopin’s Piano Sonata Op.4 No.1, First Movement

 chopin sonata op 4


Chord A
• Chord notes: Ab-C-F#-C. Remove duplicates > Ab-C-F#
• Stack in thirds: F#-Ab-C
• Chord: Contains diminished 3rd (F#-Ab) > Italian 6th
• Key: Move by semitone to find dominant: F#>G and Ab>G. G is the dominant, and C is the tonic. Following chord is G7 (V7) then Cm (i) so key is C minor.


Chord B
• Chord notes: Ab-Ab-C-D-F. Remove duplicates > Ab-C-D-F
• Stack in thirds: D-F-Ab-C
• Chord: D dim + 7th = ii°7c
• Key: Still C minor from previously (the E natural is a chromatic auxiliary note).


4. From Mozart’s Piano Sonata No.12, K332, Third Movement

mozart sonata 12 


• Chord notes: Ab-C-F#-Eb
• Stack in thirds: F#-Ab-C-Eb
• Chord: Diminished 3rd (F#-Ab) > German 6th
• Key: Move by semitone to find dominant: F#>G and Ab>G so G is dominant, C is tonic. Check next bar for major/minor. Key = C minor.


5. From Beethoven’s “Moonlight” Sonata, Op.27 No.2

 beethoven moonlight sonata


• Chord notes: F#-F#-A-D-F#. Remove duplicates: F#-D-A
• Stack in thirds: D-F#-A
• Chord: D major > simple triad with accidental foreign to key signature > presume to be Neapolitan 6th. If it’s an N6, the tonic will be a semitone lower (C#) and we’d expect it to be followed by V, V7 and/or Ic. In this case it’s followed by G#7 then C# minor second inversion, so N6 fits the criteria.
• Key: C# minor


6. From Chopin’s Prelude Op.28 No.20

chopin prelude op 28 2 


• Chord notes: D-D-C-D-F#-B. Remove duplicates > D-C-F#-B
• Stack in thirds: Not possible > presume it’s an extended dominant > check bass line > D (V)-G (I)
• Chord: D major extended. Triad: D-F#-(A omitted); 7th=C; (9th=E-not included); (11th=G-not included); 13th=B. Chord is V13a.
• Key: G major.




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