By Ben Blakesley
George’s Music

Am  -  G  -  F  -  G…
What song is that?

If you said “All Along the Watchtower,” you’re right!
If you said “Stairway to Heaven,” you’re right!
If you said “Don’t Fear the Reaper,” you’re right!
If you said you’re noticing a pattern here, you’re right!

Any musician who has been learning to play popular songs will start to notice that certain chords tend to stay together and be found over and over again.

There is a very good reason for this and can be explained with some simple music theory.  It’s all based on the key in which the song resides.

So how do you determine what key a song is in?  String along…

Major Keys

There are 12 Major Scales in Western music (we’ll stick to major keys for this example), one for each of the notes in the chromatic musical alphabet: C, C#, D, D#, E, etc, etc.

But each of these Major Scales follows the same pattern of intervals and includes the same configuration of Major, Minor, and Diminished chords.

The order is: Major, Minor, Minor, Major, Major, Minor, Diminished
In the music world, we use a Roman Numeral system where an upper case numeral indicates a Major Chord, a lower case indicates a Minor Chord, and lower case followed by ° indicates a Diminished Chord.

So the chords in a Major Scale can be represented as such:

I – ii – iii – IV – V – vi – vii° – I

Using that concept with the key of C Major, we can place each note of the scale over our Roman Numerals to extrapolate the chord that it creates

I – ii – iii – IV – V – vi – vii° – I
C – Dm – Em – F – G – Am – Bdim – C

So the reason that we so often see C, F, G, and Am together is because they are all in the same key.  And if we’re playing a song that stays in the key of C Major and is not breaking basic musical rules, it will only have C, Dm, Em, F, G, Am, or Bdim in it.

Minor Keys

Just like Major Keys, Minor Keys will follow a pattern that can be represented with Roman Numerals.
To make it even easier, you don’t have to learn a new pattern, you can simply use the same chords as the Major Key!  You see, every Major Key has what’s called a Relative Minor key associated with it.

The way you determine a Major Key’s Relative Minor is by located the iv chord in the key.

I – ii – iii – IV – V – vi – vii° – I
C – Dm – Em – F – G – Am – Bdim – C

In the key of C Major, the Relative Minor is Am.
If you’d like to play a song in Am, it’s going to contain the chords: Am – Bdim – C – Dm – Em – F – G; Just like the key of C Major!

But Mr. Ben, how can we tell if a song is in the key of Am or C major?
While there is no sure-fire way to determine this short of using your ears, there are a few clues you can be on the lookout for.  The number 1 indicator is the chord that starts or ends the song.  If it’s a C, then you’re in C major.  If it’s an Am, then you’re in Am.  For whatever key you’re in, the associated chord should feel and sound like ‘home’ when you get there.

The Chord Decoder Ring

Now that you’ve got the basics of chords and keys down, you should be able to easily identify what key a song is in based on the chords it includes.

As a reference, here is a list of some popular keys so that you can quickly see what chords are included in each of the keys (the relative minor is in bold):