Learn how to work out the four types of triad chords on the guitar fretboard.
View the full lesson at Making Major Chord Grips Into Minors | JustinGuitar
In the example using the A chord why is string 1 not played for A maj, A min and A aug (fingered on the first fret)?
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I guess it’s for pedagogical reasons given that the major/minor triad shapes are covered in sets of 3 strings in the course (1/2/3, 2/3/4, 3/4/5, 4/5/6).
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Hi @mike_upa and welcome to the JustinGuitar Community.
With A Aug and A dim you must have an E# and an Eb respectively.
You would definitely not want an E natural note in those two chords.
Therefore the open E strings are not played.
For consistency they are also muted for the A major and A minor even though those chords do contain the note E (which can be found in the shapes shown anyway regardless of the open strings).
Does that help?
Cheers 
Richard_close2u JustinGuitar Official Guide and Moderator
Yes, sounds reasonable, thank you!
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Working through this module.
An A major, so the triad is E-A-C#
Does that mean that is is a 2nd inverted Triad?
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Exactly, as the 5th is the lowest note in this triad.
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Great, thank you for confirming. Think things are finally starting to sink in:)
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In the A augmented triad, if the A and F were doubled, would that be a “full” A augmented chord?
Important correction … the note you call F should be called E# in this context.
I’m not sure what you mean by full.
I was picturing an E shape barre chord at the 5th fret playing an A chord. If I added the E# at the 8th fret on the 5th string, would that be Aaug? By full I mean all strings are played.
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@jonesdch You would still have the note E (the 5th) in that chord.
Hey Richard,
I’m on this lesson today. What’s the reason for "X"ing out the 1st string on all of the diagrams. I now understand why the 6th string E is "X"ed out as we want the base not to be an “A”
The base triad for A Major is A-C#-E
So for A-Maj and A-Min the open E string should be fine on the 1st string.
For A-Aug it seems to me you would just finger the E#(F) on the 1st string. I played it and it sounds viable.
For the A-Dim I could understand muting both open E strings. Ugly sounding chord though. Great chord to play when watching Halloween and there is a knock on the door and Michael Myers is standing there (cue A Augmented). 
If you want to stretch your brain, check out all of the possibilities for A chord shapes.
I played this by muting the 5th with my pinky. It actually sounds better (fuller) than with the open Adim. Fyi. Playing around like this is how I learn.
or
The 1st string is the note E.
That note is 100% one of the notes within the A major chord.
BUT
The entire focus of this lesson is alterning the notes / altering the chords.
The next chord in the diagram, A Aug contains E#. If the open 1st string was played also there would be a clash between E# and E.
For the A minor chord, the note E is still present.
For the A dim chord we now have Eb as one of the chord tones. If E were present also it would present another clash of Eb and E in the same chord.
Those clashes would either not sound good and /or make the chord type ambiguous.
For consistency across all four chords it is much easier to dispense with the 1st string and concentrate only on the four that are shown.
I hope that helps.
Cheers
Richard
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The augmented triads are fun, as they have the shame shape along chord, 1st, and 2nd inversion, if I am correct. Interesting to observe.
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