Key Signature in Music: Definition & Concept

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  • 0:00 Key Signatures
  • 1:45 Number of Accidentals
  • 2:36 Writing Key Signatures
  • 4:06 Reading Key signatures
  • 5:24 Minor Keys
  • 5:52 Lesson Summary
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Lesson Transcript
Instructor: Logan Wright

Logan is an active Jazz Guitarist, and classically trained composer with an affinity for contemporary musical styles.

In this lesson, we're talking about key signatures. We'll learn how to properly write them, how to quickly identify them, and why they're used in the first place.

Key Signatures

In Western music, it is quite common that a piece of music, or a melody, is predominantly based on a particular major or minor scale. When this is the case, the tonic, or first degree of the scale, is often referred to as simply the key. For example, if a piece of music is written that utilizes the G Major scale, we could say that the music is in the Key of G. Let's continue talking about the key of G Major, but first let's remind ourselves of the G Major scale.

G Major Scale In Treble Clef

As you can see, the G major scale uses one accidental, raising the F natural to an F sharp. If we were to write a piece of music using this scale, every time we used the note F on the staff, we would have to include an accidental raising it to F sharp. This can get cumbersome to read quickly, and it would be easier to simply indicate to the performer that every time we use an F, it should be considered an F sharp, from the very beginning. To do this, we use something called a key signature. A key signature is a group of accidentals that are found at the beginning of a composition and indicate the key, or the scale, that the piece is based on. This can be a bit confusing, so let's illustrate this with an example. First off, here is a melody written using the G major scale (key of G) without a key signature.

Short G Major Melody Without Key Signature

Now, let's look at the same melody using a key signature.

Short G Major Melody with Key Signature

Sure, in the examples, there aren't too many notes that require accidentals, and it doesn't save us too much time. However, for longer pieces, and more complex keys, it can make the music much easier to read and understand quickly.

Number Of Accidentals

Although there are only twelve notes in a chromatic scale, there are 15 possible keys. This is because, for theoretical purposes, enharmonic keys such as Gb and F# would be considered different. When we say enharmonic, we are making a distinction between written and sounding pitch. If two pitches are written differently, but sound the same, they are considered enharmonic. Don't worry if this doesn't make too much sense right away, we don't need to worry about it too much for the purposes of key signatures.

Okay, now let's take those 15 possible keys, and count the number of flats and sharps for each scale. Then, let's order the scales based on the number of accidentals. This will provide us with a handy reference to work back from where we're trying to find and use keys. We may also begin to see some patterns arising.

Writing Key Signatures

Writing key signatures on the staff has a very specific set of common practice rules that need to be followed. This allows performers to quickly assess what key the music is in, without spending a lot of time evaluating the key signature. As we saw earlier, each new key adds exactly one accidental to the key that preceded it. If we were to list the appearance of these accidentals in a row, it would give us the order of appearance for accidentals on the staff. Here are all the key signatures for all of the sharp and flat key signatures.

All 7 Sharp Key Signatures

All 7 Flat Key Signatures

The exact position of these accidentals on the staff will always be preserved when using a key signature, except for extremely rare circumstances. In addition to a specific order of accidentals, it's important to remember a few more constants in the world of key signatures. They always appear after the clef, and before the time signature on the first staff of a new piece. On each subsequent staff, the time signature will not be included. We will however, reiterate the key signature on each staff next to the clef.

Okay, one last thing: when we say exact position, we're not just speaking about their horizontal order; we're also speaking about the exact vertical position on the staff. This means that if we are adding an F Sharp for the key of G Major, it will always appear on the same line of the staff, as demonstrated more clearly in the graphic. Remember that this rule applies to all key signatures. You can use these examples as reference if you're unsure.

Key Signature Accidental Placement

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