Chord Qualities by Ear: Major, Minor, Diminished, Augmented

Two questions get you all four: is the fifth perfect, and is the third high or low?

Short answer: the four basic triads differ by exactly two decisions, the size of the third and the size of the fifth, and every audible difference between them follows from those two numbers. Major is a major third with a perfect fifth. Minor lowers the third by a semitone. Diminished lowers both the third and the fifth. Augmented keeps the major third and raises the fifth. Rated dissonance rises in that same order, major, then minor, then diminished, then augmented, and that ordering has been measured across every possible three-note chord rather than assumed.

The four qualities, by the numbers

A triad is three notes stacked in thirds: a root, a third and a fifth. Open Music Theory puts the rule plainly: the quality of a triad is determined by the quality of the interval from the root to the third and from the root to the fifth. Everything else follows.

Notice how small the physical change is. Major and minor differ by one semitone on one note, and that single semitone carries most of the emotional weight people attribute to whole pieces of music.

The dissonance ordering is a measurement

Johnson-Laird, Kang and Leong tested the ordering properly in 2012. Rather than sampling a handful of textbook chords, their first experiment collected dissonance ratings for all fifty-five possible three-note chords, and a second experiment covered a representative forty-eight of the four-note chords. Participants agreed with each other reliably, and the ratings reproduced the predicted trend: major less dissonant than minor, minor less than diminished, diminished less than augmented.

Their explanation is a dual-process one. Part of the effect is psychoacoustic roughness in the sense established by Plomp and Levelt in 1965, where partials close enough in frequency to excite overlapping regions of the basilar membrane produce rapid beating that listeners hear as roughness. Part of it is tonal: chords that violate the harmonic principles of the style are rated as more dissonant regardless of their roughness. A third experiment showed that consonant chords were rated less dissonant when they appeared inside a tonal sequence than in a random one, while dissonant chords outside the common practice were unaffected by that manipulation.

So the character of a chord quality is partly acoustics and partly what your listening history expects. Neither half explains it alone.

Why minor sounds the way it does

The major and minor difference has attracted more speculation than any other fact in music perception. One line of evidence points at the voice. Bowling, Gill, Choi, Prinz and Purves compared the spectra of major and minor tone collections with the spectra of voiced speech produced in different emotional states, and found that major intervals are spectrally more similar to excited speech while particular minor intervals are more similar to subdued speech. Bowling and Purves later argued the broader case that consonance itself is best explained by the advantages of recognising vocalisation, rather than by integer ratios or by the absence of spectral interference alone.

This is an account, not a closed case, and it does not license claims about what any individual listener will feel. It does explain why the association is so stable across people who have never been taught it.

The two symmetrical chords, and why they float

Diminished and augmented behave oddly for a structural reason. The augmented triad stacks two major thirds, four semitones plus four semitones, and a third major third would complete the octave. It therefore divides the twelve-note space evenly, which means every note in it is equally entitled to be the root. There are only four distinct augmented triads in the entire chromatic space, because rotating one by four semitones gives back the same three notes.

The fully diminished seventh chord does the same trick with minor thirds, three plus three plus three plus three, and there are only three distinct fully diminished sevenths. The diminished triad is not symmetric in that way, but it does contain a tritone between its root and its fifth, which is the interval that most strongly signals instability in tonal music.

Practically, this is why an augmented chord in isolation is genuinely ambiguous. You are not failing to hear its root. It does not have a unique one until context supplies it.

How to actually tell them apart by ear

Do not try to hear four things. Ask two questions in order.

First: is the outer interval a perfect fifth? Major and minor both have one, and it is the most stable interval available after the octave, so a chord with a perfect fifth sounds anchored. If the outer interval instead sounds like a tritone, you have a diminished triad. If it sounds wider than a fifth but not quite a sixth, and the whole chord seems to have no floor, you have an augmented triad.

Second, only if the fifth was perfect: is the third high or low? That is a one-semitone judgement, the same size as any minor second, and it is the discrimination most beginners find easiest because the rest of the chord is held constant.

Sing the root, then sing the third, then check against the chord. Production catches errors that recognition hides, and the third is the note worth singing because it is the only one that changes between the two common qualities.

What our games do here, honestly

We will be direct about this, because the alternative is to imply something untrue. All eleven Hearkle games are monophonic. They play one tone at a time. None of them plays a chord, none of them tests chord quality, and we do not have a chord game. If you came here from a search for chord ear training, our games will not do that job today.

What they do train is the layer chord hearing is built from. Telling major from minor is a judgement about the size of a third, which is an interval size judgement. Telling a perfect fifth from a tritone or an augmented fifth is the same kind of judgement over a wider span. Hearspan works on interval size directly, Hearfork measures how fine your pitch resolution is, and Hearsort makes you order tones by height. Those abilities transfer to chord work. They do not replace it, and we are not going to pretend otherwise.

Keep reading

• Consonance and dissonance: the roughness mechanism underneath the dissonance ordering.
• Musical intervals explained: the semitone counts the four qualities are built from.
• Scale degrees and tonal function: where each quality tends to appear inside a key.
• Equal temperament vs just intonation: why a tempered major third is restless in a way a pure one is not.

Sources: Johnson-Laird, Kang and Leong (2012), On musical dissonance, Music Perception 30(1); Plomp and Levelt (1965), Tonal consonance and critical bandwidth, Journal of the Acoustical Society of America 38(4); Bowling, Gill, Choi, Prinz and Purves (2010), Major and minor music compared to excited and subdued speech, Journal of the Acoustical Society of America 127(1); Bowling and Purves (2015), A biological rationale for musical consonance, Proceedings of the National Academy of Sciences 112(36); Triads and seventh chords, Open Music Theory; Triads and Seventh chords, Open Music Theory (VIVA); Triad, Augmented triad and Diminished triad, Grove Music Online, Oxford University Press; Truax (ed.), Consonance and Dissonance, Handbook for Acoustic Ecology, Simon Fraser University.