TonalityGUIDE - basic tonal music theory and analysis for undergraduates
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Quick Reminder: How to work out the key of a passage

Stage One (what scale?)
At its simplest a passage is in the key of the seven-note scale on which it is based (e.g. G minor, E major etc). This page helps you work out which scale is which.

To say that an extract is definitely in a particular key, you should usually be able to find at least one perfect cadence in that key. The notions of tonality and being in a key are more fully discussed in the introduction to tonality.

You can find out what scale a passage is based on by writing out the seven note names (A B C D E F G). Then use the key signature and any accidentals to sharpen or flatten each note of this scale. Remember that some notes might be chromatic (not part of the key), so you should ask whether D, for example, is usually natural, flat or sharp in the passage.

Stage Two (the circle of fifths)
Now you need to write all the flattened and sharpened notes of the chromatic scale arranged in a series of perfect fifths. The easiest way to do this is to start with the scale of C major organised in this way starting on F (you might know a reversible mnemonic for remembering this series - Father Charles Goes Down And Ends Battle):

Then, write the same series out twice more. The first series should be flats, the second the natural notes of C major and the third series should all be sharps as below. The result is a long series of perfect fifths starting at Fb and finishing on B#:

Circle the seven notes of the scale as worked out in stage one. Any group of seven notes on this series can be either of two scales:

  • a major scale starting on the second note of the group
  • a minor scale starting on the fifth note (in which case the third note of the series - the leading note - will be sharpened)

    So C#,D,E,F#,G#,A,B could be either A major - as in the first example - or F# minor as in the second.

    Remember that music does not normally stay in the same key all the way through a piece - this is discussed in key and modulation.


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