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Recognising scales from just their accidentals  can be instant. However if it’s not here’s a systematic way of determining the  scale.

1. If there is a mix of “b” and  “#” accidentals it must be a minor scale and one of G or D minor. The # accidental is the 7th note of the scale and identifies the key note e.g. F# ==> G minor, C# ==> D minor.

2. If all accidentals are sharps,  tally them against the known order of sharps in a key signature  signature. If there are gaps in the sequence, then it’s a minor scale, otherwise a major scale.

E.g. the extract has F#,C# and A# but G’s and D’s are not written with sharps.

There is a gap in the sequence of F#-C#-G#-D#-A# and it must be a minor key. The out of sequence A# is the 7th note of B minor sacle

E.g. the extract has G#-C# and F# accidentals in that order and no others.  This corresponds  to the expected sequence of F#-C#-G# in a major key. In this case A major (take the last sharp, G#, as the 7th note of the scale)

3. If all accidentals are flats,  tally them against the known order of flats in a key signature  signature. If there are gaps in the sequence, then it’s a minor scale, otherwise a major scale.

E.g. the extract has Eb and Ab  and there are B notes in the extract written without flats there  is a gap in the expected sequence of Bb-Eb-Ab  it must be a minor key. The absent Bb gives the answer to which minor key. The B natural is the 7th note in the C minor scale

E.g. the extract has Eb-Ab-Bb-Gb and Db in that order and no other.  This corresponds  to the expected sequence of Bb-Eb-Ab-Db-Gb of  a major key. In this case Db major (take the next to last flat in the key signature as the key note)

In the last 2 bars of this extract, the Bb has been removed with a natural sign and there are no other flat accidentals.  Tallying the # accidentals, there are no C# accidentals against the written C notes (note the clef change in the bottom stave) but there is a G#. D’s are not sharpened. There is a gap in the expected sequence of sharps F#-C#-G# indicating a minor scale  with G# as the 7th note giving A minor as the answer