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In addition to being able to play, it is important to have a good knowledge of the theory of music. This is both to improve your understanding of what you're playing, and to allow you to try other aspects of music, such as composition and arranging.

On this page, I will add videos and text which aim to teach some of the most important/useful aspects of music theory.

The Circle of Fifths

The first step for any theory involving keys or harmony is to draw a Circle of Fifths. This is a very important skill! It's a good idea to draw several, one after the other, until you can do it flawlessly every time. Why not time yourself! See how quickly you can draw a perfect Circle of Fifths!

Key Signatures

  • Key Signatures let you know which notes are required for any particular piece. This is related to the scale belonging to that key. For example, do you need an F natural or an F sharp. In C Major, which has no sharps of flats, you would need F natural, whereas in A Major, which has three sharps, you would need an F sharp.

  • The order of the Sharps and Flats in the key signatures is fixed and can be remembered using:
    Father Christmas Gave Dad An Electric Blanket for the Sharps and
    Blanket Explodes And Dad Gets Cold Feet for the Flats.
    You will never have a key signature which includes a C sharp, but not an F sharp.

  • In order to know which sharps/flats belong to each key, you can use a circle of fifths. When you know how many sharps/flats are needed for they key you’re working out, you can use Father Christmas etc to work out which sharps/flats are required.


  • For Major Keys, C Major is the most important, as it has no sharps/flats. It’s relative minor, a minor is the most important minor key, for the same reason.

  • Each Key Signature refers to both a Major and a minor key. These are known as the “Relative Major” and “Relative Minor”. In order to know which is correct, you will need to either hear the piece or look at a few important pieces of evidence (such as the last note, which is likely to be the key-note [or tonic], and the prevalence of accidentals [minor keys tend to include more]).


Using the Circle of Fifths and the Father Christmas method, it is easy to decipher any interval.

  • When calculating an interval, the first thing to ascertain is the “Number” of the interval. This is done by simply counting through the alphabet, making sure that you count the lower note as number 1. For example, A to C is a 3rd, A to G is a 5th etc.

  • When you know the “Number” of the interval, it is then necessary to work out the “Type” of the interval. There are five different types of intervals: Major, Minor, Perfect, Diminished and Augmented.

  • 2nds, 3rds, 6ths and 7ths can be Major, Minor, Augmented or Diminished

  • 4ths, 5ths or octaves can be Perfect, Augmented or Diminished

  • If the upper note of the interval is part of the Major Scale of the lower note, then it will be either a Major or a Perfect interval, depending on the number of the interval.

  • If not, it’s important to work out how many semitones the actual note is from that in the Major Scale.

  • 2nds, 3rds, 6ths and 7ths: Minor is one semitone lower, diminished is two semitones lower, augmented is one semitone higher (order is therefore: Diminished, Minor, Major, Augmented)

  • 4ths, 5ths or octaves: Diminished is one semitone lower, Augmented is one semitone higher (order is therefore: Diminished, Perfect, Augmented)

  • To work out the type of the interval, therefore, it is important to know the key signature of the lower note. This is done by using the Circle of Fifths and Father Christmas etc.

  • Write out the notes of the scale, then add the sharps/flats on the appropriate notes. You can then work out whether or not your upper note falls within the Major scale, and from there, work out what type of interval you have.


Click through to's interval quiz. This is customizable, so it's possible to make it easier or more difficult, depending on your comfort level. Start in C Major only, then add key signatures as you get more confident. Write out the scale for each interval. It's time-consuming, but it avoids mistakes! also has an excellent set of informative pages and tests, including a practice Grade 5 Theory Test.

When you're comfortable with intervals, try out some of their other exercises. With the circle of fifths, you should be able to manage key signature and scale recognition.

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