Thirds

The smallest skip

A third skips one letter name: C to E, D to F, E to G. On the staff it lands on the same kind of position: line to line or space to space.

See the pair

When thirds repeat, the staff creates a stable zigzag shape. Recognizing that shape reduces note-by-note guessing.

Triad building block

Thirds are the basic building blocks of triads. C-E-G is two stacked thirds, which is why thirds show up constantly in piano music.

Major and minor thirds

The staff distance can look the same while the keyboard distance changes. C-E is a major third; E-G is a minor third.

Interval quality

Thirds have quality. A major third is wider, like C to E; a minor third is narrower, like E to G.

Triad spelling

Triads are built by stacking two thirds. Major, minor, diminished, and augmented triads all begin as stacked-letter shapes, then adjust quality.

Seventh chords stack thirds

A seventh chord is four notes stacked in thirds: root, third, fifth, and seventh. The added seventh creates stronger pull and richer function.

Quality from stacked thirds

Chord quality comes from the size of the stacked thirds. Major seventh, minor seventh, dominant seventh, and half-diminished seventh chords each have a distinct stack.

Guided walkthrough

A third is the smallest skip: it skips one letter and one staff position.

1. 1Read the starting note.
2. 2Skip one letter name.
3. 3Land on the next line or next space.

Try it on the keyboard

Play C-E, D-F, E-G, and F-A while saying the skipped letter.

1. 1Count the starting letter as one.
2. 2Skip the middle letter.
3. 3Play the destination as three.

Check yourself

Can you explain why C to E is a third even though D is not played?

Theory transfer

Connect interval quality and triad spelling to the notation before playing so the theory idea becomes a reading decision, not only a definition.

1. 1Name the theory idea in one short sentence.
2. 2Point to the note, rhythm, interval, chord, or phrase shape that shows it.
3. 3Play the example once for accuracy.
4. 4Play it again while listening for the theory idea.

Analyze and compose

Use seventh chords stack thirds and quality from stacked thirds to explain what the music is doing, then make one small musical choice of your own.

1. 1Name the key or temporary key area.
2. 2Label the chord, cadence, non-chord tone, or phrase function.
3. 3Play the example while saying the labels quietly.
4. 4Compose a one-measure answer or variation using the same idea.

Short applied practice

Use the example as a one-minute transfer drill: preview the concept, play slowly, isolate the hesitation, then repeat with a steadier pulse.

1. 1Preview the clef, key, rhythm, and main pattern before playing.
2. 2Play once slowly while naming the lesson concept out loud.
3. 3Repeat only the two notes or beats that caused hesitation.
4. 4Play the full example again without changing tempo.