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4. Minor Key Issues in Trio Sonatas

Grade 8 Music Theory - Minor Key Issues in Trio Sonatas

Augmented and diminished melodic intervals are uncommon (but occasionally used) in the main skeleton outline which we looked at in the previous chapter. They occur more frequently within the melodic decoration.

The main point to remember is that dissonances should resolve by step: move from the dissonance to the nearest possible note. In most cases this will mean a semitone step.


Augmented 4ths/Diminished 5ths (The “Tritone”)

In a dominant 7th chord, two of the chord notes make a diminished 5th. For example, in G7, the notes B-F are a diminished 5th. Turned around the other way, F-B makes an augmented 4th. The term “tritone” refers to either interval.

 dominant 7th

When they are used as harmonic auxiliary notes in a V7 chord, the aug4/dim5 intervals will sound ok. V7 is normally followed by the tonic chord, and the dissonant 7th will resolve by step.

For example here, the V7 chord in A minor (E7) includes the notes E-G#-B-D, with G#-D making an augmented 4th. The augmented interval sounds fine here, as it is simply part of the chord.

 dominant 7th dim 5th

Aug4/dim5 intervals also occur when chord IV moves to chord V, if the subdominant note moves to the leading note.

In the D minor example below, subdominant G moves to leading note C# (augmented 4th) in the top part. However, the main skeleton melody moves from D (last beat) to C#, which is the smooth interval we would expect. Placing the augmented 4th into the melodic decoration softens its harshness a little.




Diminished 4th/Augmented 5th

When i (minor tonic) is followed by V, the mediant in the tonic chord can fall (rather deliciously) to the leading note in V, creating a diminished 4th.

In this example below, the prevailing key is D minor. In the top part, the first main melody note D is embellished with E (passing note) and F (auxiliary harmony note and mediant in this key). The F then falls by a diminished 4th to C# (leading note in V). Notice that the C# resolves by step to D.

 diminished 4th


In this case the dissonance is again softened because it occurs as part of the melodic decoration. However, you can also occasionally find this interval occurring within the main melodic skeleton too, with quite a dramatic effect. You can certainly use it that way, but use it very sparingly!

Choosing From the Melodic Minor Scales

Since the melodic minor scale has a raised 6th and 7th degree on the way up, but not on the way down, it can sometimes seem confusing whether you should be raising a note by a semitone or not when the music is in a minor key.

There is a certain amount of artistic licence here – sometimes either version of the scale can be used. But in some situations, you can use your knowledge of theory to guide you in your choice. It’s certainly not the case that the ascending version of the scale should only be used where the melody ascends, for example. The following examples are all in A minor.


  1. 7th degree to tonic: raise the 7th. The leading note gets its name from the fact that it has a strong pull towards the tonic. In almost all cases where the leading note is followed by the tonic, (ascending pattern), raise the 7th.
    leading note

  2. 7th degree auxiliary: raise the 7th. When the tonic note is decorated with a lower auxiliary note, the 7th should be raised. This is the same leading note function described in 1.
    auxiliary note

  3. 6th and 7th degrees to tonic: raise both. When the leading note has been raised, the 6th also needs to be raised to avoid the augmented 2nd between the 6th and 7th degrees of the scale.
    raised 6th and 7th

  4. Dominant decoration: raise 6th/7th. In point 3 above, the melody notes would fit with a dominant E major chord. When the harmony is chord V, the decoration should agree with the chord notes. So, if you use a descending scale pattern, the 6th and 7th are still normally raised.
    dominant harmony

  5. Subdominant decoration: don’t raise 6th/7th. Minor chord iv includes the unraised 6th degree of the scale (e.g. F in a D minor chord iv in the key of A minor). Decorate chord iv with the notes that agree with the chord.
    subdominant harmony



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