What Key Am I In?

A quick guide to understanding and using keys along with the pattern of chords naturally found in any key.

Sep 15, 2022

What Is A Key?

The term key refers to the note that starts the Ionian mode, which is the same thing as the Major Scale. If you don't know your modes, then check out my post about the modes as one system. Just remember that there are seven modes in the order of Ionian, Dorian, Phrygian, Lydian, Mixolydian, Aeolian, and Locrian. These modes correspond with the notes of a key. If we are in the key of C, then Ionian starts on C and the other modes start on each subsequent note in the scale. If you need to know what notes are in a key, then check out my post on the circle of fifths. This will explain in greater detail how the key of C uses the notes C, D, E, F, G, A, and B so the modes use would be C Ionian, D Dorian, E Phrygian, F Lydian, G Mixolydian, A Aeolian, and B Locrian. If we started on the key of G, then our notes are G, A , B, C, D, E, and F#. This means the modes in the key of G are G Ionian, A Dorian, B Phrygian, C Lydian, D Mixolydian, E Aeolian, and F# Locrian.

What Notes Do I Use In A Key?

The key of C is the only one that has no sharps or flats, so the real question is how do I know what sharps or flats to use in the other keys? You would first need to understand how the keys are built in the circle of fifths. As an example, we can first look at the sharp side of the circle.

The Sharp Keys

This is the key of G which uses the notes of G Ionian: G, A, B, C, D, E, F#. The alternating blue and red lines connect each natural interval with their flat or sharp counterpart. As you move around the circle of fifths you will gain either more flat or sharp notes as your natural intervals. The key of G is one step in the sharp direction, so it has only one altered noted (F#) as one of its natural intervals (the major 7th).

When we name the notes in a key, we always use each letter one time. No more and no less. In the above diagram I've matched the natural notes and their sharp counterparts to highlight how you can only use the natural note or an altered note. Looking at the keys of D, A, E, and B we can see that as we move through the keys, we are only adding one additional sharp note. The added sharp note will always be one half-step down from the keynote, so D's new sharp is C#.

To move through these keys (D, A, E, then B) you keep all the previous notes, start the next key on the fifth degree note, and sharpen the last note of the new key. So the key of A takes the notes of D, E, F#, G, A, B, C#, starts on the fifth degree note of A, and then sharpens the last note in the new key to have A, B, C#, D, E, F#, and the new note of G#.

We can keep adding sharps for the keys F# and C#. Notice that we have gained the note E# in the key of F#. E# is the enharmonic equivalent of F because they are the same note. There is a realm of theory that can prove that E# is not equal to F due to the way wavelengths of sound are built in a key, but for the sake of usefulness E# is the same tone as F.

The same thing happens in the key of C# and we gain a B#. In this key all the notes are altered to be sharp. While this may appear to be a difficult key to use, it's really the opposite idea of the key of C. C uses all natural notes. C# uses all sharp notes. While each key uses a different set of altered notes, they all use the major scale. This means that you always have the modes in the same order every time.

The enharmonic equivalents of E# / F and B# / C are used in the naming of the notes in these two keys. Without E# and B# we would have keys with multiple notes starting with the same letter of F and C. You always want to use each letter once and only once.

The Flat Keys

Now let's go to the flat side of the circle of fifths. To the left of C is F and then Bb. As we move through the flat side we gain a flat note at the fourth degree, so the key of F is F, G, A, Bb, C, D, and E. The next key is what we flattened in F and we continue to gain a flat note on the fourth degree of the scale. This means that Bb is the next key and the notes are Bb, C, D, Eb, F, G, and A. We'll continue to gain flats all the way through the key of Cb.

The keys of Gb and Cb have enharmonic equivalents of Cb / B and Fb / E. Again, the naming convention of notes has us use each letter once and only once to avoid confusion as to which letter note we play and which alteration is played meaning that a note can be flat, natural, or sharp.

If you look at the circle of fifths, you will notice that there are some overlaps between the sharp keys and the flat keys. This just means that you have some enharmonic equivalents where the following keys use the same tones, but the names are different: B and Cb, F# and Gb, C# and Db.

How Do I Quickly Figure Out What The Key Is?

Now that we are a little familiar with sharp keys and flat keys, we can look at the chords used in a song. Regardless of how your song is played, the key is where Ionian starts. This commonality allows us to know that the order of the chords is Maj7, m7, m7, Maj7, Dom7, m7, and m7b5. We can also number these chords with roman numerals as I, ii, iii, IV, V, vi, and vii˚. The capital letter for the roman numerals means the chord is major, while lower case means the chord is minor. The small circle next to the seventh chord means that it is diminished. The roman numerals themselves refer to triads, so to describe our four note seventh chords we can write them as IMaj7, ii7, iii7, IVMaj7, V7, vi7, viiø.

Comparing the keys of F, C, and G we will have the following chords. All of them are going to use the same roman numerals because the keynote tells you where Ionian starts, so the chords match the modes.

If we have a song with a chord progression of Am7, Dm7, FMaj7, then we know that the key of G doesn't work because the Dm7 and FMaj7 are not in the key. The keys of F and C have all three chords, but I would think that F is the key because the progression resolves on F. We can confirm this by checking out the next progression in the song, which could be Gm7, C7, FMaj7. While all three chords belong to the key of F, the C7 chord is the big give away because there is only one dominant 7 chord in a key, and it will always be on the fifth degree.

You can also use the pattern of major and minor chords to help figure out the key. If you have a major chord one half-step above a minor chord, then you have chords iii and IV because it's the only way to make that fit. The same goes for two major chords a whole step apart. That would be IV and V. And just like your dominant 7 chord always being at the fifth degree, your diminished chord is always the seventh degree.

You can work this out even if you only have two minor chords. Your minor chords are either ii, iii, or vi. Let's say that the interval from your minor chord's root notes is 2 and a half steps. That is the interval from iii up to vi and from vi up to ii in the next octave. I would suggest you look at the second chord of both examples, which are the vi and ii chords. The vi chord belongs to Aeolian and has a b6, while the ii has a natural 6. Aside from that, they are the same scale. So play the second chord and from the root note play either mode. When you get to the b6 and 6th degrees take note to listen to what is not clashing. That is how you can figure out what key you are in. Else, you will need one more chord to help figure things out.

But what if you have more than one dominant 7 in a song?

Keys For Non-Diatonic Progressions

Let's look at another progression: Em, Am, D7, G, G, A7, D7, G. This has eight chords that we can break up into two groups of four chords. Let's call them progression 1 (Em, Am, D7, G) and progression 2 (G, A7, D7, G). Right away it looks like we are in the key of G. Both progressions have a dominant chord of D7 resolving to G in a V to I relationship. All the other chords in both progressions fit the key of G, except for the A7 chord in progression 2.

This is because A7 is a secondary dominant. A7 does not belong to the key of G, but A7 is a fifth above a chord with a root of D. This V to I relationship allows you to play a dominant 7 chord as the V chord and then go to a major or minor chord as the I or i chord. This out-of-key chord is also called a borrowed chord because it comes from a different key. You can borrow chords as much as you like, but the general rule is that you only move out-of-key briefly. A good way to do this is to play your borrowed chord and then immediately come back to something that is in your key, which is just what progressing 2 did. It goes G, borrows A7, and returns to D7.

You'll find that a lot of rules in music theory, like using borrows for a brief moment, are just rules and are meant to be broken if it works. Of course, "if it works" is yet another rule. Now I'm not saying that you should break all the rules. Instead, you should learn why to use a rule. I'll discuss more on how to borrow chords and why later. Regardless of what you learn as the rules, know that they work and can be used to your advantage.

Overlapping Keys

When using the three keys at the bottom of the circle of fifths you’ll notice that there is some enharmonic overlap. From either side of the circle, you have five, six, or seven altered notes.

So, which set do you use? Well, if I was using another key with sharps, then I would stick with sharps. Let’s say I’m in the key of D with D, E, F#, G, A, B, and C#. Going to the key of B would give me B, C#, D#, E, F#, G#, and A#. In other words, I went from one sharp note to five sharp notes. I could also think of this as gaining four sharps, so the only thing to know as far as notes go is that I gained C#, G#, D#, and A# as altered notes. The same goes for flats. If I’m in the key of F I have F, G, A, Bb, C, D, and E. Going to Db give me four new altered notes with Db, Eb, F, Gb, Ab, Bb, and C. By note flipping between sharps and flats, you can just add or subtract altered notes.

As an example, the keys of B and Cb have the same notes with different names, yet they both start on Ionian. This means that B Ionian = Cb Ionian. The same goes for the other modes: C# Dorian = Db Dorian, D# Phrygian = Eb Phrygian, E Lydian = Fb Lydian, F# Mixolydian = Gb Mixolydian, G# Aeolian = Ab Aeolian, and A# Locrian = Bb Locrian. These modes are all out of the same position on the circle of fifths and uses either the key of B or Cb. It all depends on if you want to describe your song in sharps or flats.

Unlocking the Keys

Now you may be wondering what to do if you end up using three keys spread out around the circle of fifths. I just use the same idea from above and try to make as much sense out of one side as possible. If I have two flat keys and then one sharp to play from, then I’m going to have to use sharp notes for one key, and that’s OK. I’m not trying to memorize every note for every key. I just need to know where Ionian starts and how to build my scales/modes.

From there I can write down what I’m playing using notes and roman numerals. Now I can just play each key for what it’s worth and focus on writing a song in steps rather than trying to do it all at once. I can also experiment with sounds and work on ways to overlap the keys so that I can modulate between them in a more fluid way than just jumping into a new key.

Here's one last example with an audio clip. Listen for the Am7 as a “pivot chord” between keys. Think of the Am7 as where two keys overlap and thus let you pivot into a new key. Then listen to how the dominant 7 chords work to move towards a tonic note. In this case the tonic is F.