Lesson 06: Your first chords: major and minor triads

Lesson objectives:

• Build a triad by stacking a root, a third, and a fifth.
• Measure the two kinds of third: major (4 half steps) and minor (3 half steps).
• Flip a major triad to minor by changing one note, and explain why.

Prerequisites: Lessons 01-05 (notes, steps, intervals, scales, keys) | Previous << 05 | Next: none

This is the final lesson. It pulls half steps, intervals, and scales together into a chord you can play.

"Major sounds happy, minor sounds sad" — but what actually changes?

Everyone can hear the difference between a bright major chord and a wistful minor one, and most people assume they are built from totally different notes. They are not. A major chord and its minor twin differ by one single note, moved by one half step. That is the whole trick, and it is the perfect finale for this course because it uses everything you have built: the half-step ruler, interval counting, and the scale you already know. This lesson turns "I can hear it" into "I can build it."

Explanation

A triad is three notes stacked in thirds

A triad is a three-note chord built by stacking thirds¹. Start on a note — the root — then add the note a third above it, then the note a third above that. You end up with three notes spaced as root, third, fifth (using the interval numbers from Lesson 03)¹.

Take C as the root and use notes from the C major scale:

• Root: C
• A third above C: E (C-D-E, three letter names)
• A fifth above C: G (C-D-E-F-G, five letter names)

So the C major triad is C – E – G. Play those three together and you have a chord.

The two kinds of third decide the mood

Here is where the half-step ruler pays off. Not all "thirds" are the same size:

• A major third spans 4 half steps¹.
• A minor third spans 3 half steps¹.

In the C major triad, C up to E is 4 half steps — a major third. That lower major third is what makes the whole triad a major triad¹. The top interval (E up to G) happens to be a minor third, 3 half steps.

Now flip it. If instead the bottom third is a minor third (3 half steps), the triad is minor¹. To turn C major into C minor, lower the middle note E by one half step to E-flat:

• C major: C – E – G (bottom third C-E = 4 half steps, major)
• C minor: C – E-flat – G (bottom third C-E-flat = 3 half steps, minor)

The root and fifth do not move. Only the middle note shifts by a single half step, and the chord's whole character flips from bright to dark. That one note is the answer to "what actually changes."

Worked example (follow along)

Build the G major triad and then make it minor.

1. Root: G. A third above (from the G major scale): B (G-A-B). A fifth above: D (G-A-B-C-D). So G major triad = G – B – D.
2. Check the bottom third: G up to B. Count half steps — G, G-sharp(1), A(2), A-sharp(3), B(4). Four half steps, a major third. Good, it is major.
3. To make G minor, lower the middle note B by one half step to B-flat: G – B-flat – D. Now G up to B-flat is 3 half steps, a minor third — the chord is minor. Root G and fifth D never moved.

Your turn (faded example)

Build the F major triad, then flip it to F minor. Fill in the blanks:

• Root: F. A third above F is ______ (count three letter names). A fifth above F is ______ (five letter names).
• So F major triad is F – ______ – C.
• To make F minor, lower the middle note by a half step: F – ______ – C.

Answer: a third above F is A (F-G-A), a fifth above is C (F-G-A-B-C), so F major is F – A – C. Lower the middle note A by a half step to A-flat, and F minor is F – A-flat – C. Only the third moved.

Summary + what's next

You have built your first chords. A triad stacks a root, a third, and a fifth; the bottom third decides everything — a major third (4 half steps) gives a major triad, a minor third (3 half steps) gives a minor one, and a single half-step move on the middle note flips between them. Every idea in this course showed up here: note names, the half-step ruler, interval counting, and the scales you built.

Where to go from here: apply the same stacking to every note of a scale to get that key's family of chords, learn the interval qualities (major, minor, perfect, diminished) in full, and start naming the chords in songs you already love. You now have the foundation to make all of that make sense.