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victoria Williams Music Theory

Victoria Williams

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B5. Composition - Key and Tonality

Grade Six Music Theory Composition; Lesson 5 - Key and Tonality

What is Tonality?

All music from the era we are studying at Grade Six (17th – 19th centuries) is tonal music. What does that mean?

  • It has a key, which must be either major or minor. The key signature at the beginning of every line states the key of the piece as a whole.
  • It may or may not move through other keys (modulate).
  • The notes are mainly (but not only) taken from the scale of that key.
  • In every key, the most important note is the tonic, and the next important note is the dominant.
  • Every note in the scale can be harmonised by using one of only three chords – the tonic (I), dominant (V) or sub-dominant (IV). For this reason, they are known as the “primary” triads.

The aim is for a piece of music to have a clear, unambiguous key. With your music theory skills, you should be able to look at a score and quickly identify what key the piece is in, and whether it modulates to any new key(s).

You need to remember that the available chords are those built on each degree of the major or harmonic minor scales. This means that in a minor key, chord V is major (e.g. E major in the key of A minor) and chord vii° is diminished (G# dim in A minor). Chord III+ (augmented) is not available at all - you can't use C-E-G# in the key of A minor.


Stating the Key

The main key of a piece will be asserted at the beginning. In the Grade Six composition question this is especially important, because you will need to work out what key the music is in, in order to continue writing.

Using the key signature, we can easily narrow it down to either the major or minor of that particular key signature. But if we, for example, see a key signature of 1 sharp, how can we discover whether the music is in G major or E minor?

There are a few things we can try:

  • Work out what the likely tonic is (G or E).
  • Find a sharpened leading note (D#)
  • Work out the likely primary chords (I, IV and V, or i, iv and V) (or V7) of the underlying harmony.

Which of these factors is the most important? It is the harmony, which is the most important factor in determining key.

1. Likely Tonic
The tonic is the most important note in a piece.  It can be reinforced by:

  • Occurring on a strong beat (first beat of the bar)
  • Being accented
  • Being repeated
  • Occurring as the highest or lowest note of a phrase
  • Being approached by a leap
  • Occurring in part of a scale


2. Raised Leading Note
Seeing a leading note raised with an accidental can be a quick give-away that the music is in the minor key. However, bear in mind the following points:

  • Not all melodies contain a leading note, so the piece might be in E minor but not contain a D# at all.
  • In a descending minor scale passage, the melodic minor is often preferred, which means the leading note will not be raised.
  • An accidental may be just a chromatic alteration because it sounds nice, rather than a signal of the minor key.


3. Primary Chords
The underlying harmony is the most important factor in determining key. The majority of pieces begin with chord I. A smaller number begin with V, but it’s rare to find any other chord in this position.

Chord I is commonly followed by one of the other primary chords, so in the first couple of bars we would normally expect to find I, V and/or IV. Only chords I and V have the power to fix the key of the piece firmly in our mind. As the melody develops, any other chords can be used of course. 

Let’s now examine two simple “openings” and, by looking at the underlying harmony, try to determine whether it is the major or minor key in each case. Is this C major or A minor?


  • Bar 1 fits with both i in A minor and I in C major. (The B is a passing note.)
  • Bar 2 could fit with VI in A minor or IV in C major. (All the notes form the F major triad.)
  • C major is a better choice, because it would use two primary chords – I & IV


This opening is identical, except for the last note:


  • Bar 2 could be i in A minor or vi in C major.
  • A minor is a better choice, using the tonic triad in both bars.



Is this G major or E minor? (The piece is “Rigaudon” by Rameau.) 


  • There are no sharpened leading notes to help us. 
  • The notes which fall on the strong beats are G and B – both of these notes are in the tonic triad of the major and minor chords, so that’s no help.
  • The lowest note of the segment is E, not G.
  • There is a 6-note ascending scale of E minor. G major has only a 4-note stretch.
  • E is repeated 4 times, G is heard twice.
  • Bar 1 contains all the notes of the E minor triad, but not of the G major triad.
  • In bar 1, the notes of the E minor triad fall on the beat G-E-G-B. 
  • Bar two could be harmonised with i in E minor or vi in G major. Chord vi is not a primary chord, however. 
  • All the signs suggest that this is E minor.


Is this Haydn Minuetto in C major or A minor?


  • There is a sharpened leading note G#. However, there is also a G natural, so we need to be careful.
  • The notes which fall on the first beat of the bar are C and G#.
  • A is the highest note and is also approached by a leap, which suggests A minor.
  • C is repeated three times, A only twice.
  • Bar 1 contains all the notes of the tonic triad in C major. This is chord III in A minor – not a primary chord, and not even a normal chord in A minor, which usually has a G# which makes an augmented triad (C-E-G#).
  • Bar 2 is tricky, but could be harmonised with chord ii in C major, with the extra notes considered to be non-chord notes. In A minor it would be chord iv. This bar doesn’t help us much.
  • There are clues in these bars which point us in both directions. In cases like these, always give more importance to the harmony underlying the piece, rather than melodic clues. It is harmony which defines a key.
    Bar 2 would fit in with either key, so that leaves us with bar 1, which is clearly in C major, as the notes form a C major triad. Therefore, this piece is in C major.



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