3rds & Thirds Part B : some theoretical foundations

:joy:here it is actually already “explained”… but more will follow later… Right?

And here on with the 3rds…find the differences

But @DavidP David,…I’ll stop trying to explain, because maybe I’m doing it (probably) the wrong way …Richard will continue on his own … someday :smile:

Maybe I am missing something, Rogier

What I am missing/missed was the distinction between 3rds and thirds.

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Hey David,

From what I gather, I’m thinking ‘thirds’ as the general interval of a third between 2 notes, and ‘3rds’ as the particular interval relating to the root of the scale, chord, triad etc. I suppose all will be revealed in time. :slightly_smiling_face:

Cheers, Shane


Hey, now you’re giving it away … I would give David his own penny-drop moment :wink:

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Oh wow, praise indeed. Thanks Roger (said quietly). :slight_smile:

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Thanks for the kind words and suggestions David.

I will go back and read, refining and improving is always a good idea. I know I mention ‘fifths’ but only in a cursory manner when chord constructing.
Updating and clarification now done here

The distinction is entirely my own creation.
I am using 3rds to describe the double-stop shapes that can be played on adjacent strings as described in Part A here.

3rds on G & B strings

I am using thirds to describe intervals / distances between notes laid out in Major scales that form the basis of chord construction by ‘stacking thirds’.

In a sense, you could think of the difference as being physical vs theoretical, hands-on-guitar vs hands-on-pen & paper.

Does that help?

Almost, though a 3rd (as we have seen and will see further) does not always derive its existence and attributes by reference to the chord or the scale root note.
They are relative to other notes, not just the root note.

Well, this is why I don’t teach, and still practice reading comprehension… :speak_no_evil: :see_no_evil:
I thought I got it completely,… now there’s still a faint light burning in me… roar,

I’ll just wait patiently :blush:
Edit:I see it now,I was on the wrong (???) foot for a minute…too fast again, now I stop…

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I knew I wasnt a mind reader :slightly_smiling_face:.

@DavidP @roger_holland @sclay

I have made an edit, inserting a new introductory paragraph, to Post 3 above. I hope that improves the clarity.

I think it’s clearer that way, but that’s easy to say when the penny dropped (after your comment that it’s not always R-to -3 means 3rd), David and Shane better answer this now,
Actually, I would really like to see David’s head when he reads this, because if the penny isn’t there, you have to turn your eyes away, don’t you David? because I can’t stand it myself if I don’t get something right soon or later understood…and I often have :blush:
The devil is really in the details here :upside_down_face:

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Thanks Richard. I probably missed the clarification initially on ‘3rd vs third’. It makes sense.

Appreciate the extra detail on the perfect fifth interval.

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Hi Richard,

Just wanted to confirm this ‘thirds’ vs ‘3rds’ distinction. I’ve been studying Justins theory course for the last 18 months, and at first I was missing/misinterpreting something about this distinction.

The way I understand it now;

  1. Your use of the term ‘3rds’ is a shape based concept, sort of a ‘pre-theoretical’, practical way of introducing them on the guitar. A precursor to ‘thirds’ if you like.

  2. Your use of ‘Thirds’ is the theoretical term, the interval, the builder of chords, with varying shapes on the guitar, dependant on quality and string position.

Cheers Shane

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@sclay Good stuff Shane, and hopefully the next installment illuminates further. :slight_smile:

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The three triad shapes

Hopefully you have been able to take the time to read, scrutinise and digest the information and the diagrams above. From the triple neck diagrams in Post 17 we saw the shapes for Major triads and for minor triads. Here it is again.

The CAGED chord shapes are in the centre. These are the source shapes for the triads we will find within. On the left are the Major and minor triad shapes on the D, G and B strings. On the right are the Major and minor triad shapes on the G, B and E strings. The highlighting shows duplicate triad shapes. If we eliminate those duplicates we will see that there are only three triad shapes for Major triads and three shapes for minor triads on the string sets under consideration.

Major and minor triad shapes on the D, G and B strings

Major and minor triad shapes on the G, B and E strings

That is it.
For the top four strings, there are no other triad shapes on adjacent string sets.

Next we will start to see how these triad shapes lead to the shapes of the 3rds that we learned and began using in Part A of this topic.

Triads and thirds

A triad, within its formulation, will contain two intervals of a third. Let us return to the seven triads (chords) derived from harmonising the D Major scale. We can refer to the note circle once again to determine the nature of the two intervals of thirds within each chord formula.

Note Circle

Remember, four semitones is an interval of a Major third and three semitones is an interval of a minor third.

1] D - F# - A = D Major chord … D to F# = Major third then F# to A = minor third.

3rds 26

2] E - G - B = E minor chord … E to G = minor third then G to B = Major third.

3rds 27

3] F# - A - C# = F# minor chord … F# to A = minor third then A to C# = Major third.

3rds 28

4] G - B - D = G Major chord … G to B = Major third then B to D = minor third.

3rds 29
5] A - C# - E = A Major chord … A to C# = Major third then C# to E = minor third.

3rds 30

6] B - D - F# = B minor chord … B to D = minor third then D to F# = Major third.

3rds 31

7] C# - E - G = C# diminished chord … C# to E = minor third then E to G = minor third

3rds 32

Note the alternating pattern.
Major chord triad formulae contain Major then minor thirds.
Minor chord triad formulae contain minor then Major thirds.
The diminished chord, as usual, does its own unique thing!

This may be easier to see and recognise if the diagrams are placed in a grid pattern.

3rds 26 - 3rds 27

3rds 29 - 3rds 28

3rds 30 - 3rds 31

… … … … … … … … … … … … … … … … … 3rds 32

From Thirds to Chords To CAGED to Triads to the Shapes of 3rds

We can now revisit the Major and minor triad shapes with the intention of selecting all pairs of thirds in groups of ascending notes that either go from Root to 3 or 3 to 5. For all such pairings the notes have been changed to blue and other notes have been greyed out. A few triad shapes contain two such pairs so all three notes are blue. What we will do here is look for any repeating patterns / repeating shapes on the guitar neck. We want everything to go ‘pair shaped’. :wink:

Pairs of thirds on the D, G and B strings

Pairs of thirds on the G, B and E strings

There may seem to be many pairs of thirds (Root to 3 and / or 3 to 5) on adjacent strings within these triads. But, in fact, on close inspection, we will find that there are actually only two shapes for each pair on any given set of two adjacent strings. Just two.

Shapes of 3rds on D & G then G & B then B & E strings

In previous diagrams, the notes were shown within the CAGED structure, and the triads were shown from within those chord shapes. So each was labelled with Root, 3 or 5. We arrived at a point where the triads were shown as having either one or two pairs of thirds within. Those pairs of thirds we now view as separate shapes. We also revert to calling them 3rds.

As just mentioned, there are only two shapes on any two adjacent strings.

On the D and G string there is one Major 3rd shape and one minor 3rd shape.
Two and no more. That is all.

On the G and B string there is one Major 3rd shape and one minor 3rd shape.
Two and no more. That is all.

On the B and E string there is one Major 3rd shape and one minor 3rd shape.
Two and no more. That is all.

The 3rds in the diagram shown here deliberately show no intervals. They are not marked as Root or 3 or 5. That is no longer a necessary detail. They are only for illustrative purposes to show shapes on the guitar neck. Shapes that you fingers can make to play and make music.
Also, there are no fret numbers or marks. These shapes are movable. What the notes are, and the nature of the two notes, whilst always being 3rds, will depend on where they are played. And their ‘sound’ will depend on what they are being played over … bass notes / chords etc. More of that to come.

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