Theory for Idiots: What Key am I in?

Well, this is a lesson that has been requested a few times. I’ve mentioned ‘keys‘ and being ‘in key’ in previous videos, but I’m not sure I’ve fully explained what they are…

…so this lesson is just to clarify what I mean by being ‘in key’.

What is a Key

Many people will use the term ‘in key’ to just mean something that sounds good. This isn’t technically 100% correct.

In fact, there was a time before there was even such a thing as a ‘key’!

In medieval times, for example, they didn’t have ‘keys’. What they used instead was a system of ‘modes’ (not quite the same as the modern modes but a similar idea). These were essentially just scales, and each song would be based around a certain scale.

So, if you were a composer in Europe in the 1100’s, you would pick a scale, and use the notes of that scale to write your tune. Then, you might add in a bass-line that also used the same scale and you might have a third instrument in there somewhere.

Again, they would all be playing notes from the same scale. Then, you just have to be careful that the notes that each instrument is playing don’t clash. That’s kinda how music originally worked…

…then, things got complicated… (but not too complicated for me to explain!)

The Major Scale

What happened was, two of the modes became a bit more popular- what were to become the major scale, and the natural minor scale. It’s from these two scales that we can start making chords and have the idea of being ‘in key’.

Things have become a bit more complicated in modern times (I blame Jazz!), but that’s the short story.

So, as I explained in my lesson on chord progressions, keys go one step further. Instead of everyone in a song just using the same scale, we can now have everyone follow the same ‘chords’.

This might not seem like such a big deal, but chords are (as we know) already worked out to sound good together. I mean, in a three note chord, you can have the bass play one note, the lead play another, and then maybe a second guitar play the third note.

This is where we can move on from saying ‘this song uses this scale’ to ‘this song is in this key’.

Does the song have a chord progression that resolves? It’s probably in a key.

Is it just a tune that uses one scale over a static bass note? It’s probably using a mode.

On the Guitar

As I explain in the video, you can also hear this on your guitar. If we take, for example, the C major scale:

C major scale in 2nd position on guitar

Then, arrange the notes so that they’re all along the A string:

C major scale along the A string of the guitar

We can use A shaped barre chords taken from the notes of the rest of the scale:

The chords of C major in A shape barres on the guitar

If you’ve seen my video lesson on chord progressions, you might have already worked out what these chords are. If not, you might want to see that lesson to understand what I’m talking about a bit better!

The chords we get are: C major, D minor, E minor, F major, G major, A minor, B diminished.

So, any song that just uses those chords will be in the key of C- and it will feel ‘finished’ or ‘resolved’ on that chord.

All we’ve done is:

  • Picked a major scale
  • Built chords by only using the notes in that scale
  • Then created a chord progression from those chords

You don’t have to use all of the chords, but as long as it’s just those chords you’re using, you’ll be in the key of C major.

That’s how something gets to be ‘in key’.

For example, here is a chord progression in he key of C major:

an example chord progression in the key of C

As I demonstrate in the video, this chord progression works because I end it on a C chord. In the key of C, a C major chord sound like home. If I were to end this song on any other chord, it wouldn’t quite feel finished.

That is- in a nutshell- what a ‘key’ is, and how it works. Why not try making up some of your own chord progressions in the key of C? You could also try some different keys, if you want more of a challenge!

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