The theory on this page is written for guitarists.  Before you start, you should already know how to play some chords and songs.  Once you know it, it'll speed up your ability to understand a song and work it out by ear no end!  If you know nothing about music theory it won't seem simple, but it really is and a good teacher will cover it, using the songs you are studying as examples.

IMPORTANT.  These concepts are arranged in order of complexity, so if you are unable to grasp one, don't progress to the next until you have practised and understood it, using real songs.  It is all summarised at the end of the page, but you won't be able to learn unless you understand.

1. The Key

2. Scales and chords

Scales

Chords

Dominant chords

Relative and parallel minor

3. Working out the chords in a song

4. Notes

5. Songwriters tricks

6. Summary

The key of a song is the note or chord which sounds like home.  The other notes/chords sound like they're going around, or 'resolving', to it.  The song Burning Love, covered on page 2 of this section, is in the key of D major and sounds as though D is home.  It starts on the D chord and it feels like it is landing on D as you go along. 

Once you know the key, you can work out the likely chords and the notes of the song.  Don't progress until you know the keys of the songs you have learnt and understand why.

The 'home' chord is also referred to as the root (R), tonic or I (one) chord

A scale is made up from 7 notes (tones) which are numbered (lettered?) from A to G.  If a scale starts on an intermediate note, it wraps around, so the scale of C major comprises:  C, D, E, F, G, A, B.   It starts and ends on C, which is known is its 'root'.  A major scale sounds happy :  )

Each major scale has a relative minor.  The scale of A minor (Am) has the notes A, B, C, D, E, F, G.  Although it has the same notes as the scale of C major, it starts and ends on the root A.   This gives it a different sound to C major -  a minor scale sounds sad  :  (   So, the Am scale is the relative minor of C (major). 

Tip: on the guitar, you can find the root of the relative minor scale on the same string by counting down three frets from the root note of the major.

The scales other than C major and Am have one or more sharps (#) or flats (♭).  G major, for example, has the notes G, A, B, C, D, E, F#, G; so it won't have the same pitch as C major and will sound higher or lower.  It will sound similar, however, and happy  :  )   The scale of Em is the relative minor of G,  so......yes, it has the same notes as those of G major.  And it sounds sad  :  (

When you play scales on the piano, the visual patterns differ because of the black notes (sharps and flats).  On the guitar, the scale patterns are the same for each of the same type of scale, so if you play G major starting at G on the 6th string (3rd fret), you can move the fingering pattern up to A (5th fret) and you'll be playing A major.

Each chord is made up from 3 or more notes. The simplest chords are made up from the 1st or 'root' (R) note, the third and the fifth notes of the scale.  So, in the key of C major, these chords are:

For convenience, we number the chords I to vii  (see Nashville numbering system)

Even though theses chords have a R, 3rd and 5th, because we only use the notes from the within the scale, some of the chords are major and some are minor.  The last (vii) chord in the scale is called a diminished chord (we use the symbol °).  Don't worry about this one at this stage and don't confuse it with a seven chord, eg, G7.

So, how do we remember the chords In a major key?

The I, IV and V are major.  The others are minor (or diminished in the case of the last one)

And how do we remember the chords in a minor key:

The i, iv and v are minor.  The others are major (or diminished in the case of the second one)

Dominant chords
Very often the V chord in a key is a 'dominant' chord.  It is called dominant because it is the strongest chord in the key and sounds as though it is trying to resolve to the root.  It is indicated by the chord letter and a number, often 7, but sometimes 9, 11 or 13  eg. G7.   The fact that a dominant chord is the fifth in the key can often be used as a pointer as to which chord is the home chord, hence the key.  For example, if there is a D7, the key may well be G.   A 7 chord may not always be dominant or the fifth chord in the scale, but it's worth trying it first, when working out the chords in a song.  Note that this feeling of the dominant pulling to the tonic (the I chord) is so strong that it is often used even in a minor key, when you might expect the V chord to be minor.  So there could be a D7 as the V chord in the key of Gm.  You'll have to listen to the overall sound/feeling of the song to know whether iit is major or minor (Is it happy or sad?) and/or listen for the other chords.

Relative minor and parallel minor

So, we have said that the relative minor has the same chords and in the same order as the major key, but starting from the root of the minor key, that is why it is relative.  So, for Am the chords of C major are used, but starting from A.  A is home:

The parallel minor is not the same.  It has the same letter root as the major, but the key is minor, so the parallel minor of C major is C minor.  The chords in Cminor are different to those of Cmajor.

Note that Cm is the relative minor of E♭ major, so the chords of Cminor are also found in the key of E♭ major.

Note also that in both major and minor keys, the V chord could be dominant: in the case of the keys of C maj and Cm it could be G7.

3. Working out the chords in a song

Once you know the key, you can work out the chords most likely to be found in a song.  These will be, in order of probability, I,  V, IV, vi, ii, iii.  In the key of C, then, C, G, F, Am, Dm, Em.  In this example you'll always find C, nearly always G (or G7), nearly always F and, if more than three chords, probably Am and/or Dm and/or Em.  There are thousands of songs which only have the I, IV, V chords, and a similar number more with I, IV, V, vi.  Our example Burning Love uses the !, IV, V, vi chords (D, G, A, Bm).

It'll really pay you to learn all of the notes so that you can find them quickly and without thinking.  I suggest one of two methods:

1. learn the notes on each string one string at a time.  Start with the two E strings (1st and 6th), then A (5th string), then D (4th) then G (3rd) then B (2nd).  Or

2.  Learn to find all of the Gs, then Cs and so on.  Again, there are free apps, so you can even practise this when you're away from the guitar.  You won't do this in one day.  If you do, you'll forget them the next, so do little and often.

Intervals between notes
Each fret on the guitar has one half-step, or semi-tone, between it and the next fret.  There may be one or two frets between two notes.  One between E and F and between B and C, two frets between all the other whole notes.  So the thinnest string, the first string, has the notes E, F, F#, G, G#, A, A#, B, C, C#, D, D#, E.     # means sharp.  F# is also G flat (♭),  A# is B♭ and so on.

There are many tricks song-writers use to get away from the expected chords in order to make the song more interesting, so sometimes there'll be chords which puzzle you when you hear them.  Don't worry about them, you'll recognise some of the tricks as you develop your ear.  Here are a couple of freebies from me:

Passing through the parallel minor (the key having the same root note name, but minor - hence different chords).  A song may often do this on the IV chord before it goes home to the I.  In the Muse version of Can't Take My Eyes off You for example, which is in the key of C major, there is an F followed by an Fm before going home to C.  It has actually borrowed a chord from the parallel minor key of Cm.

Using a dominant chord from the relative minor.  As I said above, song-writers will often replace the v chord in a minor key with a dominant.  John Lennon's Imagine is in C major, but you'll find an E7 where you would expect Em.  This comes from the dominant chord in the relative minor, Am, which is E7.  It sounds awesome, though, right?

This is all basic stuff and simplified.  It will serve you really well if you know and understand it.  If you are confused, you could spend a few hours searching for the theory in a book or on the net, but you'll deal with a load of stuff you don't yet need to know along the way.   A good teacher will answer or explain anything you don't understand in a few minutes, at a level appropriate to you  :  )   The thing with theory is not to learn it as a separate subject, but to do so as you use it, and by using example songs.  This is how you really understand and internalise it.

If you really want to develop your understanding of music theory, I highly recommend Harmony and Theory: a Comprehensive Source for all Musicians in the Hal Leonard series.