Chords and Harmony I: Triads

TL;DR

A triad is a basic three-note chord built by stacking two intervals of a third. The type of triad (major, minor, diminished, augmented) is determined by the specific intervals between its notes. Understanding triads is fundamental to analyzing and creating harmony in music.

1. The Mental Model

Think of a triad as a musical "building block." It's the simplest chord you can make, and all other, more complex chords are essentially built by adding more blocks onto these basic triads.

2. The Core Material

A triad is a chord made of three notes. These notes are stacked in specific intervals of a third. The bottom note is called the root, the middle note is the third, and the top note is the fifth.

How to Build a Triad

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You start with a root note. Then, you add a note a third above it. Finally, you add another note a third above that second note (which means it's a fifth above the original root).

Let's use C as our root.
1. Root: C
2. Third above C: E (C-D-E, that's three scale steps)
3. Third above E (Fifth above C): G (E-F-G, that's three scale steps; C-D-E-F-G, that's five scale steps)
So, a basic C triad is C-E-G.

Types of Triads

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The specific quality of a triad (major, minor, diminished, augmented) depends on the exact size of those two stacked thirds. Remember, a third can be a major third (4 half steps) or a minor third (3 half steps).

Here's how they combine:

graph TD
    A["Start with a Root Note"] --> B{First Interval (Root to Third)};
    B --> C["Major Third (4 half steps)"]
    B --> D["Minor Third (3 half steps)"]

    C --> E{Second Interval (Third to Fifth)};
    D --> F{Second Interval (Third to Fifth)};

    E --> G["Major Third (4 half steps)"] --> H["Augmented Triad (R, M3, Aug5)"];
    E --> I["Minor Third (3 half steps)"] --> J["Major Triad (R, M3, P5)"];

    F --> K["Major Third (4 half steps)"] --> L["Minor Triad (R, m3, P5)"];
    F --> M["Minor Third (3 half steps)"] --> N["Diminished Triad (R, m3, dim5)"];

• Major Triad: Root + Major 3rd + Minor 3rd. (Example: C-E-G. C to E is a Major 3rd; E to G is a Minor 3rd. C to G is a Perfect 5th.)
  • Intervals from root: Major 3rd (4 half steps), Perfect 5th (7 half steps).
• Minor Triad: Root + Minor 3rd + Major 3rd. (Example: C-Eb-G. C to Eb is a Minor 3rd; Eb to G is a Major 3rd. C to G is a Perfect 5th.)
  • Intervals from root: Minor 3rd (3 half steps), Perfect 5th (7 half steps).
• Augmented Triad: Root + Major 3rd + Major 3rd. (Example: C-E-G#. C to E is a Major 3rd; E to G# is a Major 3rd. C to G# is an Augmented 5th.)
  • Intervals from root: Major 3rd (4 half steps), Augmented 5th (8 half steps).
• Diminished Triad: Root + Minor 3rd + Minor 3rd. (Example: C-Eb-Gb. C to Eb is a Minor 3rd; Eb to Gb is a Minor 3rd. C to Gb is a Diminished 5th.)
  • Intervals from root: Minor 3rd (3 half steps), Diminished 5th (6 half steps).

Notice that Major and Minor triads have a Perfect 5th between the root and the top note, while Augmented triads have an Augmented 5th and Diminished triads have a Diminished 5th.

3. Worked Example

Let's build a G minor triad.

1. Start with the Root: G
2. A minor triad needs a minor third above the root.
   • A major third above G would be B (G-A-B is 4 half steps).
   • So, a minor third above G is B-flat (G to B-flat is 3 half steps).
   • Current notes: G, Bb
3. Next, a minor triad needs a major third above its third.
   • The third is Bb. A major third above Bb is D (Bb-C-D is 4 half steps).
   • Current notes: G, Bb, D
4. Check the interval from the root to the fifth.
   • G to D is a perfect fifth (7 half steps). This confirms it's a minor triad.

So, the G minor triad is G - Bb - D.

4. Key Takeaways

• A triad is a three-note chord built by stacking two intervals of a third.
• The three notes of a triad are called the root, third, and fifth.
• The quality of a triad (major, minor, augmented, diminished) is determined by the specific sizes of the stacked thirds.
• A Major triad has a Major 3rd and a Perfect 5th above the root.
• A Minor triad has a Minor 3rd and a Perfect 5th above the root.
• An Augmented triad has a Major 3rd and an Augmented 5th above the root.
• A Diminished triad has a Minor 3rd and a Diminished 5th above the root.

Common mistakes to avoid:
- Confusing "third" (the note name in the triad) with "major third" or "minor third" (the interval size).
- Not consistently counting half steps when identifying interval sizes.
- Forgetting that the type of triad is based on both stacked thirds, not just the first one.
- Miscalculating the quality of the fifth from the root (e.g., calling a diminished fifth a perfect fifth).

5. Now Try It

Pick three different root notes (e.g., F, A, Eb). For each root, build all four types of triads: major, minor, augmented, and diminished. Write out the three notes for each triad and mentally (or physically on a keyboard) verify the half-step intervals between the root and third, and the third and fifth, for each one. You'll know you've got it when you can quickly build any type of triad from any starting note and identify its quality.