Part Three — What the Ear Reports
Theory describes what composers write. Experiments ask what listeners hear. The answers are clearer than one might expect, and more modest.
For most of history, claims about the tonic were made by people who already knew where it was. A composer or theorist would examine a score, identify the key, and describe how the music behaved. The circularity is obvious once stated: the expert's sense of home was used to confirm the expert's theory of home. The twentieth century finally asked ordinary listeners.
Expectation as meaning
The groundwork was conceptual. In 1956 the philosopher and music theorist Leonard B. Meyer published Emotion and Meaning in Music, arguing that musical feeling arises largely from expectation: from the listener's anticipation of what comes next, and from its fulfilment, delay or denial. On this view the tonic is the most expected event of all, and the authentic cadence of Part Two is a promise kept. Meyer's book was theoretical, but it framed the question in terms that could be tested.
The probe-tone experiment
The test arrived in 1979, when the psychologists Carol Krumhansl and Roger Shepard published a study of what they called the tonal hierarchy. The method was simple. Listeners heard a short context, such as an ascending major scale with its final note missing, and then a single "probe" tone. They rated how well the probe completed the context. Each of the twelve chromatic notes was tested in turn.
The results traced a striking shape. The tonic received the highest ratings, followed by the fifth and third, then the other scale notes, with notes outside the key rated lowest. In 1982 Krumhansl and Edward Kessler refined the method with chord progressions and produced detailed "key profiles" for major and minor keys. The profiles matched, with remarkable closeness, how often each note actually occurs in tonal music.
Home is not a note the composer owns. It is a judgement the listener makes, again and again, as the music unfolds.Part Three
Finding the key by machine
If listeners carry something like a key profile, a machine with the same profile should be able to find the tonic too. Christopher Longuet-Higgins had already built early computational key-finders in the 1970s, and Krumhansl's profiles became the basis of an influential algorithm. David Temperley, in The Cognition of Basic Musical Structures (2001), refined the approach and showed that fairly simple statistical models identify the key of most tonal pieces within a few bars. Fred Lerdahl, building on his 1983 work with Ray Jackendoff, modelled the distances between keys and chords in Tonal Pitch Space (2001).
Learned from exposure
Why should frequency of occurrence and perceived stability line up so closely? David Huron's Sweet Anticipation (2006) offers the most persuasive answer we know: listeners learn the statistics of the music around them, largely without awareness, and their sense of what is stable reflects what they have heard most. Huron's account makes the tonic partly a product of exposure. It is home because, in a lifetime of listening, it is where melodies have most often gone.
Cross-cultural work supports this, with caveats. A 1984 study by Mary Castellano, Jamshed Bharucha and Carol Krumhansl compared Indian and Western listeners hearing North Indian rāgs. Both groups picked up the tonal hierarchy of the music they heard, especially the importance of Sa and the fifth, but the Indian listeners showed sensitivity to subtler structures specific to each rāg. A shared capacity, then, shaped by particular histories.
What the evidence allows
We can now state a careful conclusion. Listeners, including untrained ones, reliably perceive a hierarchy of stability with the tonic at its peak. That perception correlates closely with exposure, and it rests on the acoustic advantages described in Part One. What the evidence does not support is the stronger claim that tonality is a law of nature, binding on every ear. It is, more precisely, a very deep habit with a physical foundation. And deep habits can be tested by breaking them, which is what Part Four examines.