Tonality

Tonality, or musical key, is the central organizational principle of pitch in common-practice Western music. It provides a hierarchical arrangement of the 12 pitch classes per octave, such that individual pitch classes vary in their stability, both in a music-theoretical and psychological sense. Stable pitch classes are points of musical rest, such that the passage sounds relatively complete, and does not require movement to resolve any lasting tension. In the key of C major, the highest level of the tonal hierarchy is the tonic tone (pitch class C), followed by the other pitches of the tonic triad (E and G), then the remaining diatonic pitches (in the key) of D, F, A, and B. The other five pitches not found in the key (nondiatonic – C#, D#, F#, G#, and A#) form the lowest level of the hierarchy. The assignment of pitch classes to levels of the tonal hierarchy is relative—if the piece modulates to a new key, say G major, then the tonal hierarchy shifts with it, such that G, B, and D form the tonic triad. The tonal hierarchy of a minor key is similar (tonic triad: A, C, E; diatonic: B, D, F, G; nondiatonic, A#, C#, D#, F#, G#) but the diatonic/nondiatonic collection can slightly vary, based on what form of minor scale is in use (natural, melodic, or harmonic).

The reason that the tonal hierarchy is so fundamental to Western music is because it provides an efficient and effective mental framework that listeners automatically and involuntarily use to encode, represent, and remember pitch information. Pitches in a melody are encoded by their function in the tonal hierarchy, and less stable pitches are “anchored” to those higher in the hierarchy. Events that occur on tonally expected events are processed faster and more accurately than for lesser expected events, for any number of unrelated tasks. It also causes asymmetric interference with temporal judgments, and can override violations of temporal expectancies. Tonality is a critical component of both short- and long-term memory for melodies, influencing recognition, similarity, and recall. It is also a basic component in forming expectancies about what pitches will come next, which in turn are a vital mechanism for emotional expression in music. Last, without tonality, music sounds disordered, unpleasant, and aesthetically deficient.

Carol Krumhansl provided the most comprehensive investigation of tonality in music psychology. She quantified the tonal hierarchy through experiments comprised of providing a key-establishing context (e.g., scales, chords, or chord cadences) and collecting behavioral responses to subsequently played probe tones. She used a variety of tasks to investigate the psychological representation of tonality, such as completion, similarity, and recognition. Figure 1 shows the goodness-of-fit judgments of all 12 chromatic pitch classes for both C major and C minor (natural), averaged across a variety of musical contexts.

Figure 1Krumhansl-Kessler tonal hierarchy. Goodness-of-fit each all 12 pitch classes for (a) C major tonality and (b) C minor tonality.

Using multidimensional scaling analysis of intercorrelations among major and minor probe-tone profiles, Krumhansl derived a spatial representation of tonality, where the placement of individual keys on a four-dimensional toroidal (donut-shaped) map indicated their relative psychological distance. This map respects the principles of the circle of fifths, relative major/minor, and parallel major/minor and is similar to Werts' theoretical map of keys. Tonal hierarchies are not limited to Western music, although their exact form is culture specific. The few commonalities in tonal systems across cultures (such as octave equivalence and presence of perfect fifth) may reflect an underlying physiological foundation from which different musical systems developed.

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