An Introdution to Music Theory

19 Nov An Introdution to Music Theory

I am sure you will already be aware that songs are played in a particular key signature and using a given scale within that key. In this article I will try to explain, with examples, just what this means.


The Pentatonic Scale

There are many types of scales but the majority of blues and blues based rock is played with the minor and major pentatonic shapes (with a few variations such as the flat 5th or blue note). Pentatonic being a five note scale.

This is the scale of A pentatonic minor with the root (A) on the 6th string.

Here is the same scale with a change of position that will allow you to go higher up the neck i.e. “the extension box”.

This is a different version of A minor pentatonic starting with the root on the 5th string. This is an octave higher than the previous one, as indicated by the 8va above the stave.

The A Major Pentatonic scale with the root on the 6th string


And again the A Major pentatonic with extension box.


This is the same scale starting with the root note on the 5th string, again the 8va indicating played one octave higher than written.


The A Natural minor scale. There are seven notes in contrast to the pentatonic’s five,


If you compare them – A B C D E F G with A C D E G you can see that the pentatonic minor is an abbreviated version. The Pentatonic minor scale has no 2nd and no 6th note.


A Natural minor starting with the root on the 5th string.


This is the A Major scale with the root note on the 6th string. The seven notes are:


A B C# D E F# G#, in comparison with the pentatonic’s five A B C# E F#, so again it can be seen that the pentatonic is an abbreviated scale. The Pentatonic Major scale has no 4th and no 7th note.

and A Major one octave higher with the root note on the 5th string.


Essentially all of these scales are movable because they contain no open strings. All of the above examples are in the key of A minor or A Major because they start with the A note on either the 5th or 6th string. To change key simply move the scale to the root note required and as long as the same shape is played then the notes will be correct for the key.

For example, if the above scale is moved down to the D note at the 5th fret of the fifth string and the same shape is played then the notes D E F# G A B C # D will be played , i.e. the D Major scale.

If the very first example (A pentatonic minor with the root A on the 6th string) is moved up to say the 12th fret E note then the scale is E minor pentatonic E G A B D.


Relative keys

If you compare the A minor scale A B C D E F G A with the C Major scale C D E F G A B C

you will see that they have the same notes, just starting from a different position.

Therefore these two scales are referred to as being relatives and this is true of every key.

Major Key                  C      Db      D       Eb      E       F       F#      Gb      G      Ab    A       Bb     B

Relative Minor         Am   Bbm   Bm   Cm   C#m   Dm   D#m  Ebm   Em   Fm  F#m   Gm   G#m

On the guitar to find a relative minor key simply move down (flatten) by three frets.

i.e. A Major to F# minor, F# is three frets lower than A,

C Major to A minor,  A is three frets lower than C.

If there are any questions, don’t be afraid to ask. Failing that there is always SKYPE. I hope this will solve the ‘mystery’ of where to play on the fretboard for someone.

Robert Taylor

51 years old. AC/DC fan since I was 11, I live and breathe their music and first got a guitar because of Angus' playing. I'm an intermediate level Guitar player. Likes blues based Rock 'N' Roll bands. I'm easy going, interested in life, people and nature. Gear: 1970 Gibson SG, 1977 Ibanez Artist AR2622eq; 1979 Marshall 2203, 1971 Marshall 1960A Cab, Cetec Vega Diversity Dynex 2, and TSR No.36.

  • avatar
    Posted at 04:56h, 01 December

    I’m sorry I messed up on my comment below. Touch too much is not in G Major but in E minor. Same key signature though. Same with Let there be Rock. (At least I think Let there be Rock is E minor. I personally think it switches key signatures especially during Angus’ solos. It ends with a B chord so It could be in E minor since it is the 5th tone of the scale).

  • avatar
    Posted at 06:16h, 29 November

    I’m a little confused about AC/DC’s music theory. Lets say an AC/DC song is in the Key of A Major. I’ve noticed that these songs usually involve the G chord. Why? I think its because in the blues we have a Flat 7th. In the key of G is sharped and is the 7th tone of the scale so it makes sense that they use a G chord instead of a G# Chord. Anybody have any thoughts?

    (I have this guitar tab book for AC/DC and even though I don’t learn songs from it, today I looked the key signatures. It says:
    Let There Be Rock-Key of G Major
    For Those About To Rock-Keys of D Major and A Major. (Yes they Switch)
    Touch Too Much-Key of G Major.
    I don’t know, it doesn’t seem right to know. Anybody know anything?)

    • avatar
      Posted at 11:25h, 29 November

      You are quite correct my friend, in the key of A major or indeed the major scale the 7th note is sharpened i.e G#. The big difference between major and minor is the 3rd (major)or flat 3rd (minor). When playing power chords the notes are 1st, 5th and 8th (octave of first) so the third is not heard. For A this would be A, E, A. This allows the minor pentatonic scale to be played over the major(ish) backing. i.e A C D E G and also allowing the chords A C D E G to be played.
      This is the musical equivalent of wearing your underpants on the outside but don’t it sound good! I hope this answers your question 🙂

      • avatar
        Posted at 06:12h, 30 November

        It does. Thank you. Looks like I need to brush up on my pentatonic scales.

  • avatar
    Posted at 00:37h, 28 November

    Nice. I love music theory. I’ve been studying it in school. I took a music appreciation class last year. We learned a lot of this stuff but some I have forgotten. haha. It really came in handy with my piano playing.

  • avatar
    Posted at 17:57h, 23 November

    Nice, i like the section which shows the notes to fretboard very usful


  • avatar
    Posted at 16:18h, 22 November

    Nice article, I understand some great musicians don’t care about the theory and they play with their soul instead, but I think theory is very interesting!

  • avatar
    Posted at 21:39h, 21 November

    Good summary, thanks for posting. Just understanding the pentatonic scales and how they map to the fretboard is probably the most important concept for a rock/blues beginner to grasp. Helped me a lot.

  • avatar
    Posted at 18:36h, 21 November

    I can only say same as Fil, i needed this to, i sat down some days and tried as much as i could understanding note symboles from several books i got, but no matter how much i read it wont do it, note symboles and signs is like bird foot prints to me, or chinese alfabeth(no offence if anyone here is from china ofcourse), it simply wont ”get in” for me, i’d rather use my ear and watching from the eyes how you can do it, i cant remember what all induvidual signs and symbols stands for either so it’s kinda pointless to me, but this was actually understandable, screw books this works much better!

    Thanks for sharing! 🙂

  • avatar
    Posted at 07:37h, 20 November

    I needed this, thanks Rob

  • avatar
    Posted at 21:18h, 19 November

    Veeery interesting (-:

  • avatar
    Posted at 20:06h, 19 November

    Could be made for me. Thanks!

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