Could someone give me a stacking thirds for dummies kind of explanation.
If you start out with C, stacking thirds on top of it means making a chord out of the note a third above C (in the scale of C major), then a third on top of that, etc.

So, the C major scale is C D E F G A B.

A third above C is E, so we have CE; an interval of a third.

A third above E in the scale is G, so we have CEG; the chord of C major.

A third above G in the scale is B, so we have CEGB; the chord of Cmaj7.
^That would be stacking diatonic thirds.

Stacking thirds can also be stacking major thirds. C up a major third E up a major third G# up a major third C=C E G# C=C+ chord.

Or stacking minor thirds. C up a minor third Eb up a minor third Gb up a minor third Bbb (same as A, but must be written as B double flat)=C Eb Gb Ebb=Cdim7 chord.
Also diminished thirds, and augmented thirds are rarely used in stacking thirds.
for the TS, i am sure you only need the first response.

you just take a scale, here it is c major, and build chords using every other note.

C D E F G A B C D E F G A B C
r   3   5   7   9  11  13

this is how each note gets its respective scale degree.
next you need to learn the chord formulas and voila, you can make any chord.

this may be covered in the sticky FAQ.
im pretty sure there isn't a such thing as a Diminished or Augmented third. correct me if i'm wrong, but can't there only be a diminished versions of an interval if there is a such thing as a Perfect (insert name of interval here) so like a perfect fourth, then diminished and augmented fourths.
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Quote by djsteiner
perfect fourth, then diminished and augmented fourths.

i though fourths could only be perfect or augmented, because wouldn't a diminished fourth be the same as major third? please correct me if im wrong
Quote by linfield44
i though fourths could only be perfect or augmented, because wouldn't a diminished fourth be the same as major third? please correct me if im wrong

the sound is the same but you have to call it diminished.
i think we all need to learn something.

major intervals

diminished - minor - major - augmented

if you flat a major interval twice it is diminished... like in a dim7 chord, the 7th is double flat.

perfect intervals

diminished - perfect - augmented

edit - all the info is here http://www.musictheory.net/lessons/html/id31_en.html
Last edited by branny1982 at Feb 9, 2008,
Quote by bangoodcharlote
^In what context would you need to use a diminished/augmented third? I've never heard of it.

Hmm, wouldn't diminished/augmented thirds lead to very strange triads if you stacked them? Could you, for, example, stack an augmented third on top of a diminished third, which would make, in enharmonic terms, a sus2 chord?

Or couldn't you make a diminished third on top of diminished third chord, which would be enharmonic to an inversion of some strange 7sus2 chord or something?

Or augmented third over augmented third, which would make something akin to a 7sus4?

Oh, and to actually address bangoodcharlote's question:

It seems that a diminished third would be useful in describing some strange altered scale that would be enharmonic to having 1 b2 (natural)2 4 5 6 7. It doesn't seem like it would come up often in regular diatonic scales, but it could if you altered the normal WWHWWWH pattern of the major scale to something like HHWWWWW.
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Last edited by seedmole at Feb 9, 2008,
Quote by bangoodcharlote
^In what context would you need to use a diminished/augmented third? I've never heard of it.

well, i don't know where you would use them... thats up to you i suppose, i only know what i learnt!

major intervals turn minor when flatted. if you flat them again, they are diminished.

this is the difference between a m7b5 and a dim7... the major 7 is diminished.

as far as augmented major intervals, then there are many #9 chords out there.

i appreciate you are asking specifically about 3rds, to which i cannot answer, i am sure somebody could but i'm not experienced enough
There was nothing obvious on Wiki or Google, so I'm guessing that augmented thirds don't exist.

Or, as Gpb put it, they can theoretically exist, but you could also theoretically throw a pen in in the air, have it land on its point, go to work, come home, and have said pen still on its point.