Key signature

Tonal system is based upon Major and minor scales but the reference scale is C maj that

  • Begins with C
  • Has neither flat nor sharp
  • forms the following tone-semitone succession:A more comprehensive approach is to consider major scale as two disjointed tetracordsThis presentation displays two symetrical patterns T-T-S

Reproduction of Tetrachord in either directions requires some adaptation to keep the pattern of tone and semitone

← Each tetrachord adds a flat                                  Each tetrachord adds a sharp →
Two scales with a fifth apart have a common tetrachord and one with an adding alteration (sharp in ascending progression,flat in descending progression

Begining a scale on each degree of the C Maj scale requires mainly additionnal sharps to keep the maj scale pattern

Scales sorted by increasing number of sharp produce an ascending progression of fifths

Scales sorted by increasing number of flat produce an ascendig progression of fourths

put together

In equal temperament Gb and F# are enharmonic (sound the same) and close up the progression

Since the scale is made of 7 notes,7 possible flats and sharps are available.

However we saw in the previous page that 6 flats and sharps yield the same note
Gb/F# said enharmonic (in our modern tempered system) so the progression closes up forming the so called Fifths cycle

Combination of the 7 flats and sharps would produce ,including C maj, 15 theorical scales ,but due to enharmony only 12 scales are available.

0 and 6 are common,7 are excluded (6 closes up the circle)

Tonalities with sharps.

The order of the sharps is a fifth series:F C G D A E B:
The Last sharp of the key signature is the seventh degree(leading tone ) of the scale so the tonality is half a tone higher

For example Key signature = 3# tonality=A maj

Conversely what is the key signature of B maj?

Last sharp is A# Key signature=5 sharps

As seen previously, the last sharp of the key signature is the seventh degree(leading tone ) of the scale then comes the third degree,the sixth etc

the complete serie is

Tonalities with Flats

The order of flats is a fourths series: Bb Eb Ab Db Gb Cb Fb

Tonality is given by the flat before last

for example : Key signature= 4 flats
tonality=Ab maj

The trick is one flat. The tonality is F Maj to be learn by heart

Key signature is the flat after tonality

For example : key signature of Db maj ps 5b

The last flat is the Fourth degree of the scale then comes the first, the fifth and so on…. in the reverse order of the sharps one

Tonalities of minor scales

As previously mentionned Tonal system is composed of major and minor scales. So a key signature shares two scales:

    • a major scale
    • a minor scale called « relative » whose tonic is a minor third below

So C Major → A minor

In transposition we don’t need to bother to know if the scale is major or minor in the first instance, just decide how many sharps or flats to add or to remove.

The difficulty is then to adapt the accidentals of the two minor scales

  • The Harmonic scale with its sharped Seventh degree in ascending and descending scale as well
  • The two Melodic scales with their 6th anf 7th degree altered in going up and both degree natural in going down
    Those two melodic scales are independant
    but under this presentation melodic scale it’s sometimes called Rameau’scale

Key signature of Major and minor scales

Key signature of Church modal scales

Church modes are based on C Major scale. Each degree of the C Maj scale becomes the tonique of a scale with neither flat nor sharp.

A practical method to find the key signature of those transposed modes is to build a sort of sliding rule.

  • The fixed part reads key signature
  • the moveable part indicates the fifths circle

By coinciding the tonic of the mode with 0
Key signature is given by the corresponding tonality

Example:Key signature of F on Dorian scale

Dorian = D mode so D=0
Tonality= F so 3b

As a whole


A  new tool indicates the key signature of a given tonality in the different church modes.

It is specially useful to know which mode you’re in

What mode is it?

By coinciding the given tonality (here D) with 0

Key signature is given for each mode: Here 2b reads E=Phrygian mode