Third Intervals: Major and Minor 3rd Quiz on the Staff

The third is the heart of tonal harmony. Chords are built by stacking thirds, and the quality of the third decides whether a chord sounds major (bright) or minor (darker).

1. Visual shortcut: spotting a third on the staff

The skip rule: in a third, the two notes skip exactly one position, so both notes are of the same kind.

If the lower note is on a line, the upper note is on the next line (above or below).
If the lower note is in a space, the upper note is in the next space.

There is one free position (a line or a space) between the two notes. Example in treble clef: E4 (first line) and G4 (second line), with F4 between them.

2. Reference table

There are four types of thirds, according to the number of half steps (UK: semitones) they contain:

Interval quality	Half steps	Harmonic classification
Diminished 3rd (d3)	2	Conditional dissonance (enharmonic to a major 2nd)
Minor 3rd (m3)	3	Imperfect consonance
Major 3rd (M3)	4	Imperfect consonance
Augmented 3rd (A3)	5	Conditional dissonance (enharmonic to a perfect 4th)

3. Identify thirds

These exercises train the difference between major and minor thirds in different key signatures and clefs.

4. Build thirds

A root note appears on the staff. Choose the type of third and click the position of the second note.

5. Printable third worksheets (PDF)

The same two skills, on paper: one sheet to identify written thirds and another to write them. Each has 42 melodic third intervals in treble clef spread over seven staves, starting with natural, ascending notes —the major and minor thirds that come out of the natural scale— and ending with sharps and flats and mixed directions. No exercise repeats the same two notes.

Identify thirds

Under each interval there is a line to write what kind of third it is and whether it ascends or descends (M3 ↑, m3 ↓…).

Printable PDF worksheet with 42 melodic third intervals in treble clef to identify — A4 sheet with 42 melodic thirds to identify.

Download the worksheet (PDF A4) Answers

Write thirds

The reverse exercise: the first note and the interval to form are given, and the student places the second note on the staff, with its accidental if it needs one.

Printable PDF worksheet to write 42 melodic third intervals in treble clef — A4 sheet with 42 melodic thirds to write.

Download the worksheet (PDF A4) Answers

You may print and photocopy them freely for the classroom. Each answer sheet is the same worksheet with the answers in red, so you correct by laying one over the other. The rest —including the sheets that mix several intervals— is in interval worksheets in PDF, and if you want new sheets every time or to practice on screen choosing the intervals, in the custom interval quiz.

Music dictionary: intervals →

← Seconds

Fourths →

To train your ear as well, use the reference tones of the online tuner and compare the sound of each interval with a pure tone. The online metronome helps you build sight-reading speed.

Frequently Asked Questions

How many types of thirds are there?

The two common ones are the major 3rd (4 half steps, such as C–E, F–A and G–B) and the minor 3rd (3 half steps, such as D–F, E–G, A–C and B–D). There are also the diminished 3rd (2 half steps, enharmonic to a major 2nd) and the augmented 3rd (5 half steps, enharmonic to a perfect 4th). Both are rare in tonal music.

How do you recognize a third on the staff?

A third joins two positions of the same kind (line to line or space to space) with one position skipped in between. It is one of the easiest intervals to spot, because the notes sit close together but are separated by one position.

Why are thirds so important in harmony?

Because triads are built by stacking thirds: root, third and fifth. A major third plus a minor third makes a major triad (C–E–G). Two minor thirds make a diminished triad. The mix of major and minor thirds decides the character of the chord.

Which thirds in the C major scale are major?

The major thirds are C–E (degrees 1–3), F–A (4–6) and G–B (5–7). The other thirds of the scale (D–F, E–G, A–C, B–D) are minor thirds.

How are thirds related to chords?

Every triad is two stacked thirds. Major third below and minor third above: major triad. Minor below and major above: minor triad. Two minor thirds: diminished triad. Two major thirds: augmented triad.