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Music Theory:

Key & Tonality

Now it’s time to put into practice what we learned in the previous sections about scales and chords. If we use the notes of a Major scale to build the chords and melody of a song, it stands to reason that the result will have a certain coherence, consistency of sound and that we will perceive the first note of the scale, the Tonic, as the foundation of this musical construction.

We noticed how the chord on the fifth degree, the Dominant, tends to go back, to 'Resolve' to the chord on the Tonic and we examined a few examples of Cadences, progression of chords that lead back to the Tonic that we will call the ‘Tonal Centre’.

All these elements together form the ‘Tonality’ of a song or composition or of a part of it. When we say that a song is in C Major or that we’re playing in G minor, we mean that all the chords and melodies are coming from those scales and that we perceive a Major or minor character or atmosphere centered on the Tonic. In fact, it’s quite usual (but absolutely not mandatory) for a song to start or end (or both) on the Tonic.

If we know the Tonality or the scale, we know what chords we can use but what if we don’t know? One of the most frequent questions from students is ‘how do I find the key of a song?’ or ‘what scale can I play over these chords?’.

A song could have just a few chords or a melody that doesn’t use all the notes in a scale and that could confuse us.

Obviously, there are strategies: let’s go back to our Major scale and observe the sequence of chords it generates.

If we have chords with a seventh extension, things get quite easy, two consecutive chords will yield all seven notes of the scale but we might not get so lucky.

We can see that two minor chords a whole tone apart can only be the second and third degree while two Major chords a whole tone apart must be the fourth and fifth.

If we find a Dominant 7 or half-diminished chord we hit the jackpot, no doubt there.

Keep in mind that there is no guarantee that the Tonic is even among the song’s chords and that there may still be chord combinations that leave some ‘hole’ in the scale and in those cases, unless the melody comes to our rescue, we can decide the tonality among the possible choices: we’ll go deeper into that concept in the Modes section.

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If we consider the relative minor scale, all the chord types will be shifted up two places, now the I chord is a minor 7th and the Dominant is on the VII.

The rules still apply but we must relate them to the relative Major scale unless we want to learn the new chord sequence.

The Tonality has changed to A minor, the mood, the atmosphere has changed but the key (you haven’t explained what it is yet!) is still the same.

Notice how now the Dominant on the 7th degree tends to go to the Tonic and also the m7 on the fifth wants to resolve there (V - i) though it’s not an attraction as strong as the V - I: our mind has shifted into minor and wants to stay there.

If you want a stronger cadence, you can switch to the Harmonic scale and use the Dominant chord on the fifth or the Diminished on the seventh degree.



You don’t have to use the 7th extension of the I chord if you don’t want those dissonances or you could just ‘borrow’ those chords from the Harmonic scale.

The Harmonic scale has a very peculiar sound, it defines a Tonality but we may just use a chord or two from this scale in a song that has another Tonality without radically changing it but just adding a color, a different texture or tension by momentarily altering just one note in the scale (G# in our example). Borrowing chords and altering notes is a very common practice when composing or arranging music and is different from ‘modulating’ to another key (again?) when we make those alterations either permanent or long-lasting.

Actually, in this example, adding a G# wouldn’t change the key, it would just be an ‘accidental,' an altered note: there is no key with just G#, you can’t just add random accidentals to the score, as we will see in the next chapter when we finally will tackle keys and modulations.


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