[Chaotic Kittie]

I was thinking about diminished chords and augmented chords... primarily.
I've never seen them, and so I'm wondering what intervals that are in them, so I can start finding them on the neck. It'd also be nice to have a tab showing a way of taking them.

Feel free to tell me about any other kind of chord you think may be worth mentioning!

[Fretsource]

The boring theory part
Diminished chords are chords made up of stacked minor third intervals. That means it's made up of notes that are stacked up and separated by minor third intervals .
Another way to look at them is as minor chords with a flat fifth instead of a 'perfect' fifth
For example, B D F is a B diminished chord. (B D F# is a B minor chord).
That kind of diminished chord is called a diminished triad because it only has three different notes and you won't find them much in songs outside of jazz or classical.

Other types of diminished chord are the diminished seventh chord, which is a diminished triad plus another minor third. This makes an interval, known as a diminished seventh (one smaller than a minor seventh)
B D F Ab - is B diminished seventh - and is much more common than the diminished triad.
Another type of diminished chord is the 'half diminished seventh' which is the diminished triad plus a minor seventh interval. It's called 'half diminished' because the last note was made by adding on a major third interval instead of a minor third.
B D F A - is B half diminished seventh. (F to A is a major 3rd)
This type of chord can also be called Minor seventh flat fifth because it's exactly the same as a minor seventh chord except it has a flat 5th.

Augmented chords are made of stacked major thirds:
For example C E G# is an augmented chord.

The useful practical part
Two common and completely moveable shapes for diminished seventh and augmented chords are: (example F)
F Dim7
XX3434

F Augmented
XX3221

A special property of diminished 7th and augmented chords is that any of the notes in it can be the root. (the chord's name)
I called the above example F dim 7, but I could equally correctly have called it, B, D or Ab dim 7 - without moving it!!
Same goes for the augmented. It can also be called, A, or C# augmented, instead of F augmented

[Kirk Lorange]

Nicely put, Fretsource.

It's also worth noting that, unlike other scales that are irregular in pattern (like the major scale's W W h W W W h), the diminished and augmented scales are regular:

Diminished is W h W h W h W h
Augmented is W W W W W W W W

The upshot of that is that the shapes of the chords generated by those sacles can move up or down the neck and still be 'the chord' ... in other words any diminished chord shape, on any string set, can move up or down the fretboard in 3 fret jumps and still be that chord ... a new inversion perhaps, but it's still the same chord. Augmented chords jump up and down the fretboard in 4 fret increments.

Therefore, for all practical purposes, there are but 3 diminished chords, and but 4 augmented chords.

[sustain66]

Hello Kittie, this site should really help. It's simple but technical, and to the point. Great resource! http://www.all-guitar-chords.com/guitar_scales.php?qqq=1&scch=C&scchnam=Major&get2= Get