Koch begins with poetry, where long and short syllables reveal how rhythm can organize motion before harmony even enters the picture.

Koch borrows the idea of metre from poetry, where combinations of long and short syllables form recognizable feet. A trochee moves long–short, an iamb short–long, while spondee and pyrrhic use equal values. Music can imitate these patterns, but their meaning depends not only on duration: metrical stress can make equal notes feel unequal in weight.

The three-syllable feet extend the same principle. A dactyl moves long–short–short, an anapaest short–short–long, while tribrach, molossus, and other feet organize further combinations. Koch treats the note on an accented beat as structurally long, even when all written values are equal. Thus rhythmic identity arises from accent and position, not notation alone.

This explains why two theorists might name the same surface rhythm differently. One may follow the bar line, another the phrase opening, another the hierarchy of strong and weak beats. For Koch, the decisive factor is often perceived weight. Poetic feet are therefore useful models, not rigid labels: they reveal recurring rhythmic shapes without exhausting music’s possibilities.

Once a rhythmic motion has been established, the listener expects continuity, even when melodic decoration disguises the pattern on the surface.

A composition teaches the ear how to move. Once a characteristic metrical motion is established, an abrupt change can feel awkward because the listener has already formed an expectation. This matters especially in dance music, where a gavotte, bourrée, or gigue may survive imperfect harmony more easily than a damaged rhythmic profile. Lose the dance pulse, and the genre itself begins to blur.

Melodic figuration complicates the picture because ornament can hide the original pattern. Diminutions, passing notes, and changing note values may alter the surface while leaving the underlying metre intact. Koch therefore distinguishes appearance from function: the composer may vary the melody freely, provided the basic movement remains perceptible and the listener can still sense the same metrical identity beneath the decoration.

In multi-voice music, that identity need not remain in the soprano. The characteristic rhythm may pass to the bass, alto, or tenor while another part becomes freer. What matters is that at least one voice continues to project the principal movement. This allows imitation, variation, and redistribution without losing coherence: the metre belongs to the whole texture, not to a single melodic line.

Koch’s practical rule is simple: when the main melody stops articulating an expected stress, another voice must often step in.

The first problem occurs when the melody has a rest exactly where the established movement expects an attack. If every part is silent there, the pulse can seem broken. Koch therefore requires another voice, often the bass, to articulate that point. The principle applies to both beats and smaller subdivisions: an expected metrical division should remain audible somewhere in the texture.

The same need arises when the melody sustains a note longer than the active metrical unit. In 2/4, a quarter note can function as the beat while the eighth is submetrical; in 6/8, the dotted quarter and eighth fill those roles. A held soprano may span several such points, so another voice supplies rhythmic support and keeps the established movement audible.

Syncopation makes the principle clearest. When a note begins on a weak division and is tied across a strong one, another voice should normally mark that strong beat, especially with successive ties. In Bach’s two-part inventions, this creates the metrical framework against which displacement is heard. Without that contrast, syncopation loses its tension and becomes mere suspension.