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Key signature

The key signature is a set of sharps or flats placed at the beginning of the staff. It corresponds to the key (or tonality) of a musical work.

Position

The key signature is placed at the beginning of the staff, between the clef and the time signature. In classical music, the key signature is indicated on each staff, while in jazz, it is usually indicated on the first staff of each instrument and then omitted on the following staves.

FIGURE 1 - Two-sharp key signature
2-sharp key signature (F and C )

FIGURE 2 - One-flat key signature
One-flat key signature (B )

Effect

Unlike accidentals, the sharps and flats of the key signature are valid for all bars of the staff on which they are placed and for any octave.

FIGURE 3 - The key signature is formed by two sharps (F and C). All Fs and Cs of the song are sharped, regardless of the octave to which they are placed.
2-sharp key signature (F and C )

FIGURE 4 - The same piece (previous figure) written without any key signature, but with accidentals. Sharps are added within the score.

Remember that an accidental is valid for its octave only, but until the end of the bar in which it is placed.

Sharps and flats series

Sharps or flats in the key signature always appear in the same order. For example, a two-sharp key signature will always include F and C, in that order. Thus, knowing the number of sharps or flats allows to deduce the corresponding key signature. Since there are 7 notes in the scale (A to G) and each note can be altered (by a flat or a sharp), there are in all seven key signatures with sharps and seven key signatures with flats possible.

It is important to memorize the sharps and flats series in order to easily read, write or find any possible key signature.

Sharps series

F - C - G - D - A - E - B

Flats series

B - E - A - D - G - C - F

Note that the flats series corresponds to the inverse order of sharps series.

From key signature to key

From the key signature, it is possible to deduce the key of the work. Each key signature has two possible keys, one major and the other minor. These keys are referred to as 'relative'. The following methods are used to find the major key, the minor key can be deduced from it.

Key of a key signature with sharps

When the key signature consists of one or more sharps, the major key corresponds to the last sharp of the signature raised by one degree.

Example 1
In a 3-sharp key signature, the last sharp is G.

F C G D A E B

G + 1 = A

FIGURE 5 - A Major signature

The key corresponding to a 3-sharp signature is A Major.

Example 2
In a 6-sharp key signature, the last sharp is E.

F C G D A E B

E + 1 = F

FIGURE 6 - F Major signature

Beware! Here, the F is part of the key signature (1st sharp of the series), so it is already sharped: the key of a 6-sharp signature is therefore F Major.

Key of a key signature with flats

When the key signature consists of several flats, the major key is given by the penultimate flat of the key signature.

Example 3
In a 2-flat key signature, the penultimate flat is B.

B E A D G C F

FIGURE 7 - B Major signature

The major key of a 2-flat signature is B Major.

Example 4
In a 5-flat key signature, the penultimate flat is D.

B E A D G C F

FIGURE 8 - D Major signature

The major key of a 5-flat signature is D Major.

Be careful to take into account the flats included in the signature. In key signatures with flats, the penultimate flat is flat by definition, the major key will always be a flat key, as in Examples 3 and 4.

Special case: F Major

When there is only one flat in the signature (that is B), a problem arises because there is no penultimate flat. This is the key of F Major.

FIGURE 9 - F Major (1-flat key signature)

Key without key signature

When there is no key signature, the major key is C Major.

FIGURE 10 - C Major (empty key signature)

From key to key signature

We have seen how to find the key from a given key signature, let's now look at the opposite process.

From a given key name, it is first necessary to determine whether to look for a sharp or a flat key signature. For this, there are three simple rules to know.

1. If the name of the key has a flat, its signature will consist of several flats.

2. In all other cases (that is, if the key name has a sharp or nothing at all), its signature will consist of several sharps.

Exceptions to the second rule: C Major has an empty key signature and F Major has a one-flat signature.

Once determined whether the key signature is a flat or sharp one, it remains only to find the number of sharps or flats constituting the signature.

Key signature with flats

From a flat key, you have to go through the flats series until you find the name of the key you are looking for, then add an extra flat.

Example 5 — A Major
In this key name, there is a flat (A ). Its signature therefore has flats. We follow the flats series until we reach A and we add the following flat.

B E A D G C F

The A Major key therefore has a 4-flat signature: B E A D.

Example 6 — G Major
In this key name, there is a flat (G ). Its signature therefore has flats. We follow the flats series until we reach G and we add the following flat.

B E A D G C F

The G Major key therefore has a 6-flat signature: B E A D G C.

Key signature with sharps

From a sharp key, it is necessary to go through the sharps series until finding the note lower of a degree to the name of the sought key.

Example 7 — F Major
In this key name, there is a sharp (F ). Its signature therefore has several sharps. We follow the sharps series until we reach the note lower than F, that is E.

F C G D A E B

The F Major key therefore has a 6-sharp signature: F C G D A E.

Example 8 — B Major
In this key name, there is no sharps nor flats. This is not a special case (neither C Major nor F Major), so its signature has several sharps. We follow the sharps series until we reach the note lower than B, that is A.

F C G D A E B

The B Major key therefore has a 5-sharp signature: F C G D A.

Example 9 — D Major
In this key name, there is no sharps nor flats. This is not a special case (neither C Major nor F Major), so its signature has several sharps. We follow the sharps series until we reach the note lower than D, that is C.

F C G D A E B

The D Major key therefore has a 2-sharp signature: F C.

Be careful not to mix the processes to find the sharps and the flats signature. Also take the time to know if you are looking for the signature from the key, or the key from the signature. Otherwise you risk to apply the wrong method and get inconsistent results!

Remember the two special cases that are C Major (no key signature) and F Major (1-flat key signature).

All rules previously seen are valid only for major keys. Minor keys can be derived from major ones. The relationship between major and minor keys will be dealt with separately.

Conclusion

All these rules may seem complex for a beginner but, with training, they end up becoming automatic. Moreover, by dint of repetition, one ends up retaining a key and its corresponding signature, so that the rules to deduce from one another become accessory.

Last update on 2021/05/07

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