Teach Yourself Music Theory – 14.) Key Signature

A key signature is a marking of sharps or flats found at the beginning of a piece of music (or section) right after the clef. It is used to tell the performer what pitches are to be sharpened/flattened throughout, which pitch collections are used, and what is the center of tonality.

First, let’s take a look at the sharp keys:

With every sharp, the respective major/minor key goes up a perfect fifth. Also, notice that the addition of sharps in the key signature form a pattern of { F# – C# – G# – D# – A# – E# – B# } and are placed in there respective place on the staff lines.

So, if the piece has one sharp in the key signature, we can tell that it is in either G Major / e minor and that we must play F# throughout the entire composition.

Now, let’s take a look at the flat keys:

Once again, we can see a similar pattern with the respective major/minor key going DOWN a perfect fifth with each flat added to the key signature. Also, the flats work in a backwards pattern from the sharps, going { Bb – Eb – Ab – Db – Gb – Cb – Fb } and still be placed on the correct line of the staff.

So, if the piece has four flats, we know to lower those notes down and play in the equivalent pitch collection of an Ab Major / f minor key.

Okay, so now how do we tell what key a piece of music is in?

  1. First, check the key signature to decipher how many sharps or flats it has.
  2. Second, look at the beginning and end of the piece and see what scale degree it lands on.
  3. Third from the information gathered, make a educated conclusion as to where the music is focused around – a major or minor key.

And there you go. Unfortunately, there are some exceptions to the guideline, but above all gather information and make a supportive conclusion as to where you think the piece of music lives in – being either a major or minor key within the given key signature.

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