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III.11Part III, Tonality
Finding the key of a piece
After this lesson, you'll know how to tell, from a key signature, whether a piece is in the major key or in its relative minor.
7 min6 questionsDanhauser § 148 and 149
Since two relative keys share the same key signature, the signature alone cannot tell you which one a piece is in. With four flats, for example, you are either in A♭ major or in F minor. So you need a way to decide.
The main clue: the note the two keys do not share
Look in the first few measures, or bars as British musicians say, for the note that is not common to both scales. You already know which one it is: the dominant of the major key, raised a chromatic half step, or chromatic semitone, to become the leading tone of the minor key.
if that note is not altered, the piece is in the major mode;
if it is raised a chromatic half step, the piece is in the relative minor.
With four flats, the dominant of A♭ major is E♭. If E♭ stays untouched, you are in A♭ major; if you see an E natural, you are in F minor, whose leading tone is E♮. Danhauser illustrates this with two themes by Beethoven. Here are two melodies built on the same principle, so listen to both.
Four flats, an E♭ that is never altered, and an ending on A♭: this is A♭ major.The same key signature, but with E♮ as a leading tone and an ending on F: this is F minor.
A second clue: the final bass note
You can also identify the mode from the bass note that ends the piece, since that note is almost always the tonic. It is best to use this clue only to confirm the first one if some doubt remains.
Practice: for each key signature, give the two possible keys.
Which MAJOR key has this key signature?
Method: with sharps, the major tonic is a half step above the last sharp; with flats, it is the second-to-last flat (F major for one flat). The relative minor is a minor third lower.
Exercisein the method's spirit
Find the key of each of the following three fragments (fragment 1: 1 sharp; fragment 2: 2 flats; fragment 3: 3 sharps).
Solution
Fragment 1: the key signature belongs to G major or E minor. With D#, the dominant of G raised, and an ending on E, this is E minor. Fragment 2: the key signature belongs to B♭ major or G minor. F is never raised and the fragment ends on B♭, so this is B♭ major. Fragment 3: the key signature belongs to A major or F# minor. With E#, the dominant of A raised, and an ending on F#, this is F# minor. The E in measure 2 is an unaltered 7th degree in a descending motion, and it does not change the conclusion.
In the next lesson, you'll meet the keys that lie closest to any given key: its closely related keys.
Check your understanding
6 questions
1.
With 4 flats in the key signature, what are the two possible keys?
2.
Which note should you watch to tell two relative keys apart?
3.
What key is this fragment in?
4.
What key is this fragment in?
5.
With 1 sharp in the key signature, a D# in the first measures points to:
6.
Why is the final bass note only a confirming clue?
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