Once we have established our key or major scale that we wish to use, the next step is to harmonise these notes to form chords. Chords are simply notes played together simultaneously. Basic chords are called Diads (two notes) & Triads (three notes) which are formed of two or more notes played together. There are essentially five basic types of chord tonalities or moods that we can get:
The most used/essential chord types are Major and Minor. Often suspended, diminished and augmented chords are used as a way to maximise the impact of major and minor through creative use of dissonance and consonance (more on this later).
SO HOW DO WE FORM CHORDS?
There is a very simple method of forming chords from the major scale. Lets look at C major for this example:
C D E F G A B C
To find chords in the key of C we just have to play every other note until we have three notes to form a triad:
C E G= C major chord
Now lets start from the note D and build a chord from this note:
D F A=D minor chord
You can continue this method to find out all the notes to all the chords that are present within the key of C.
Wait a minute...why is it a major chord when starting from C but a minor chord starting from D?
That’s a good question. Well apart from the sound the notes make when played together - C E G sounds ‘happy’, D F A sounds ‘sad’, the name of the chord is created by using the individual notes own major scale.
The names ‘major’ and ‘minor’ relate to the intervals between the notes. For example with a C major chord the interval between C and E is a major third apart, with a C minor chord (C Eb G) the interval between C and Eb is aminor third.
Major means a larger gap.
Minor means a smaller gap.
Major third? Minor third? I’m still confused... Let’s look at the C major scale once more, only this time lets assign numbers to each note:
So as we already know, to form a C major chord we need the notes C E G. If we look at the numbers of those notes in relation to the numbers assigned with the scale we have:
1 3 5
Now lets look at the D major scale and assign numbers to it:
We can see the notes to a D major chord are:
D F# A
The numbers of these notes are also:
1 3 5
Now lets look at that D minor chord that confused us in the key of C:
D F A
So obviously it is not a D major chord because it has an F instead of an F#. The 3 has now been flattened (b3). This is known as a minor 3rd. It is now:
1 b3 5
The 3rd is the the tonal quality that gives the chord its distinct major or minor sound. To turn a major chord into a minor all we have to do is move the third down a semi-tone (flatten the note), to turn a minor chord into a major chord we raise a b3 by a semitone (one fret).
This numbering system ALWAYS relates to the notes own major scale. We will go over it again a little bit later, but now you have been introduced this numeric way of thinking in terms of building chords, its time to really dig our heels into this concept. Take a look at the table below:
Remember these numbers relate to the key of a individual note. To reiterate if we want to work out for example the notes for a Cdim (diminished) chord. We look at the notes of the C major scale:
We then assign numbers to the notes, then look at the numeric spelling of a diminished chord and flatten notes accordingly:
1 3 5 C E G = Cmaj
1 b3 b5 C Eb Gb = Cdim
If we want to work out the notes of an Edim (diminished) chord. We look at the notes of the E major scale:
Assign numbers to the notes, look the the numeric spelling of a diminished chord (1 b3 b5) and flatten accordingly:
1 3 5 E G# B = Emaj
1 b3 b5 E G Bb = Edim
Now we have an understanding of how chords receive their names lets continue with harmonising all the notes in the key of C:
Thats how you know which chords to play in a given key. The example here is C Major, therefore the most prominent chord would be C. This is home base. Most popular music is written from the seven chords we get when we harmonise the notes of a major scale.
For example the most popular easily recogniseable chord progression is:
I IV V
In the case of C Major this would be:
Cmaj Fmaj Gmaj
You would then create melodies using the notes from the C major scale. Instant song.
Try working out the chords in other keys to really get a grasp on this concept.
Hope you've found this helpful, let me know in the comments.
Taken from my book series 'Six String Enigma'
The AB Guide to Music Theory Vol 1
Chords And Scales For Guitarists
Ultimate Scale Book Pocket Guide Guitar Tab Book
Guitar Fretboard Fluency: The Creative Guide to Mastering The Guitar