As discussed in the previous topics, scales represent a pitch collection, centered around a tonic pitch. Because we can transpose these pitch collections to center around any pitch-class, we create twelve unique pitch centers–called keys–and even more if we include enharmonic equivalents. Because writing accidentals for many of these keys would be clunky and difficult to read, we use a system of key signatures to give the performer a simple way of knowing which pitches in the key are raised and lowered.
Diatonic music is built around perfect intervals, although as we will see below, introducing one non-perfect interval to a series of perfect intervals creates the major scale and consequently diatonic tonality. Because of this non-perfect interval, key signatures follow a very simple pattern that can be reversed whether you are raising or lowering pitches.
In the examples below, you will find sets of three keys. Use these to find:
Please note that any scale that shares a tonic note is considered to be one key. Even though this may contradict your intuitive thoughts, this means that G major and G minor are considered the same key! Instead, we call them modes of each other, not different keys. The explanation for this terminology is best left for once we have more tools to examine it, but for now, practice using the correct terminology to avoid a confusing “re-learning” moment later in the course.
Use these examples to determine the order of sharps. Pay particular attention to which scale degrees are affected in each key as sharps are added. Is it the same scale degree in each key? How is this related to the tonic? If you continue the pattern, are you able to discern the name of the next key and which accidentals are added? You should also be able to determine the relationship between a major key and its parallel and relative minors.
Use these examples to determine the order of flats. Pay particular attention to which scale degrees are affected in each key as flats are added. Is it the same scale degree in each key? How is this related to the tonic? If you continue the pattern, are you able to discern the name of the next key and which accidentals are added? You should also be able to determine the relationship between a major key and its parallel and relative minors.
In the next topic, we will discuss how the overtone series creates our perception of pitch, tonality, and music as a whole. But for now, we can observe that one aspect of the overtone series, the circle-of-fifths, plays a critical role in defining diatonic function and key signatures. The order of sharps and flats follows a series of ascending perfect 5th intervals.
Note that the two orders are simply reversed sequences of each other.
Your ultimate goal for key signatures should be the ability to instantly recall all key signatures from memory, but there are two common tricks that you can use to find the major key implied by any key signature.
Of course, these tricks do not work for C major (no sharps or flats) or F major (one flat), but you should be able to remember those two keys.
You can combine the two tricks above with your knowledge of relative major and minor keys to quickly find the implied minor key of a key signature, because relative major and minor keys share a key signature. For example, if you know that a key signature of four sharps implies E major, you can go to the sixth scale degree of E major to find the tonic of the relative minor–in this case, C#. Therefore, E major and C-sharp minor both share a key signature of four sharps.