I am going to show you how to find the key when you have just a written piece of music in standard notation and also when you just know the chord progression.
Determining the Key From a Piece of Music in Standard Notation
To find the key when you see a piece of music in standard notation, you must look at the key signature. The key signature is located at the beginning of the line (for more info on the key signature refer to my lesson on Reading Notation and Tablature). This is where sharps and flats in standard notation are placed. Their are either sharps, flats, or neither in the key signature. Sharps and flats are never mixed together. You can determine the key by counting the number of sharps or flats in the key signature as long as the key signature does not have 5 sharps or flats. You must use a more complicated process to determine the key if this occurs. Here is a chart to show you the key if you have 4 or less flats or sharps in the key signature.
|Number of Sharps||Key||Number of Flats||Key|
|1||Key of G||1||Key of F|
|2||Key of D||2||Key of Bb|
|3||Key of A||3||Key of Eb|
|4||Key of E||4||Key of Ab|
When there are no sharps or flats, it is the key of C.
Now, to find out which notes are sharp or flat, we will use the circle of fifths.
If you can remember that the 1st sharp is F# and the 1st flat is Bb, then you will have no problem finding the sharps or flats in a key signature. Figure 3 will show you how to find the sharps or flats in a key signature.
To determine the sharps, you must find F# on the circle of fifths. F# is the 1st sharp. Now go clockwise 1 place. You land on C#. This is the 2nd sharp. Continue this process of going clockwise to get the 3rd, 4th, and 5th sharps. There are only 5 because if you continue this process to find the 6th sharp, you will find F which is not a sharp.
To determine the flats, you must find Bb on the circle of fifths. Bb is the 1st flat. Now go counterclockwise 1 place. You land on Eb. This is the 2nd flat. Continue this process of going counterclockwise to get the 3rd, 4th, and 5th flat. There are only 5 flats because if you continue this process to find the 6th flat, you will find B, which is not a flat.
Now comes the hard part… finding the key when there are 5 sharps or flats. When there are 5 sharps or flats, it gets tricky because there are 3 keys that use 5 sharps or flats. These keys are B, F#/Gb, and C#/Db. All 3 of these keys have the same 5 sharps or flats. The difference between these keys is the notes that are not sharp or flat. In the key of B, those notes are B and E. In the key of F#/Gb, those notes are B and F. In the key of C#/Db, those notes are F and C. You must know these notes so that you can determine the exact key because the only way to determine the key now is to find those 2 notes used in the song. For example, if you see a B being used, you have eliminated C#/Db from being the key. Then you must seek find either an E or an F to differentiate between the key of B and the key of F#/Gb.
Finding the Key from a Chord Progression
To find the key of a chord progression, you must have some knowledge of chord progressions. If you recall, certain degrees are major and certain degrees are minor. To find the key from a chord progression, do the following:
- Write down all of the chords
- Write down the scales associated with each chord. (ie: If you have E minor, write down the E minor scale. If you have E major write down the E major scale. Do not, however, write down any modes. Just write down major and minor scales.)
- Look at each scale and see if the chords’ root notes are within that scale. If they are, that is the key you are in.