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Theory 101 – Key Signatures 1

Posted by Ian on March 16, 2008

I’m about to be gone to San Diego for a few days with my family, and am likely to not be able to update this blog.

So, before I go, I think I’ll give you all a good sized theory lesson to chew on a bit…

Today’s theory lesson will try to give you a basic understanding of major key signatures and the chords and scales

associated with them. I will go into minor key signatures at a later date, but for now will stick to the

straightforward major keys.

Each key has a corresponding set of seven notes, and seven basic triads (which I have discussed earlier): one for

each note.

First let’s take a look at the key of C. The notes in the key of C are as follows:


There are no flats or sharps: every note is natural.

The 7 basic triads are:


The pattern of chords applies to all all major keys: the first chord will be major, second and third will be minor,

fourth and fifth major, sixth minor, and seventh diminished.

To show why this happens, I will construct a C major chord and a D minor chord in the key of C

Root: C

The third and fifth scale degrees of the key of C (since the root note is C) are…


Leaving you with the root of C, Third of E, and Fifth of G… making a Cmaj chord.

Things become trickier with the D chord in the key of C.

Root: D

The third and fifth scale degrees in the key of D (we use the key of D because D is the root note) are

D E F# G A B C#

Leaving us with the triad of D, F#, and A, or the D Major Chord

However, this chord is not in the key of c, as it has a note that is not in the key of C in it, F#.

To fix this, we need to lower the F# one half step to make it an ‘F’.

This leaves us with D, F, and A, which form a D Minor chord.

You see, the chords that are in a key are always modified in this same pattern to fit the specific key.

Therefore, you should be able to figure out all chords in any given key, assuming you know the notes in the key.

Let’s take the key of Eb major.

The notes in the key are:

Eb F G Ab Bb C D

The basic triad chords in the key will be

Eb Major
F Minor
G Minor
Ab Major
Bb Major
C Minor
D Diminished

It is as simple as plugging the notes of the key into the pattern.

An understanding of the basics of key signatures is a great advantage when coming up with chord progressions.

A basic chord progression that can be derived from any key is the key’s ‘Cadence’

It consists of the 1st (tonic), 4th (subdominant), and 5th (dominant) chords of each key.

Let’s construct the Cadence for the key of A

The notes in the key of A are

A B C# D E F# G#

The basic triads are:

A Major (1st, and Tonic)
B Minor
C# Minor
D Major (4th, and Subdominant)
E Major  (5th and Dominant)
F# Minor
G# Diminished

The tonic chord is A, the subdominant chord is D, and the dominant chord is E.

The Chords A, D, and E form the key of A’s Cadence.

Looking back, the key of Eb Major’s Cadence is Eb, Ab, Bb.

You can use your understanding of key signatures and their chords to write music the flows, or merely understand

why the songs you’re playing have certain chords in them.

I am going to try to put out a followup to this lesson within the next few days that will explain 7th chords and

how they fit into different keys, however, for now, I believe I have given you enough information for one day.

Happy ukein’!

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