What is the difference between an augmented and diminished triad?

Answer 1

Using Interval, Augmented is triad with major 3rd over major 3rd from root note while a diminished triad is minor 3rd over minor 3rd from root note.

Example: C E G# Augmented

C Eb Gb Diminished

Answer 2

Diminish means to make smaller and augment means to make bigger.

From a major triad to a diminished triad- Lower the third and the fifth. This will make the notes closer together so we are diminishing the chord.

From a major triad to an augmented triad- Raise the fifth. This will make the notes further apart so we are augmenting the chord.

Answer 3

I would suggest thinking about this as stacks of thirds rather than as changes to another triad. As I’m sure you recall:

Major Chord: Built as a Major 3rd between the root and the middle note and then a Minor 3rd between the middle and top note

Minor Chord: Built as a Minor 3rd between the root and the middle note and then a Major 3rd between the middle and top note

SO then

Diminished Chord: Two Minor 3rds

Augmented Chord: Two Major 3ds

This is how you would describe the four basic triads theoretically and it has the benefit of not needing to be referenced to another chord.

Example: Exam says “Build a diminished triad on the following note” and there’s a D written. You’d just write a minor third (An F) and then another minor third (An Ab) and you are done. It helps you know what enharmonic notation to use. Here, F to Ab is a minor third…and F to a G# is an augmented second and would NOT be correct .

I’m not suggesting the previous answer is wrong, simply incomplete.