Before phrases can form a period, they must already sound as though they belong to the same musical world in key, motion, gesture, and design.

Koch separates compatibility into two levels. The first is expressive feeling, which belongs to taste and artistic judgement; the second is the material design of the phrases themselves. Technical correctness can be taught, but a convincing connection also demands cultivated taste. Composition therefore begins before invention, through attentive contact with good music.

On the technical side, Koch names five tests: unity of key, agreement of metre and tempo, likeness of internal motion or melodic figures, compatible punctuation formulas, and a sensible relation between phrase lengths. None works alone. A phrase may be correct in itself yet still sound foreign if its cadence, pacing, or rhythmic proportions contradict its neighbours.

This is why Koch treats listening and performance as part of compositional training. By singing, playing, and studying repertoire, the student absorbs tonal behaviour, metrical character, phrase balance, and stylistic expectation almost passively. Such experience gives rules a living context. The ear learns what coherence feels like before the hand learns to reproduce it deliberately.

Once key and metre are stable, coherence depends chiefly on how phrases end, how long they last, and how their internal motion relates.

Two phrases in the same metre can still conflict if their inner activity differs too sharply. Koch therefore considers the movement of beats and subdivisions, including what we would call harmonic rhythm. A gavotte whose harmony changes mainly by quarter-note beats establishes a metrical habit. Later phrases should respect that internal motion unless a clear musical reason justifies a contrast.

Melodic figures create another kind of continuity. A new phrase need not copy the preceding one, but it should normally develop a recognizable musical vocabulary through continuation, variation, or transformation. Koch’s principle resembles coherent speech: variety is welcome, but unrelated topics produce confusion. Good periods balance continuity, contrast, and a shared stylistic identity.

Cadences and phrase lengths are equally relational. Successive punctuation formulas should be similar enough to belong together yet varied enough to avoid monotony. Length works the same way: four, six, or eight measures are not good or bad in isolation. Their value depends on proportion, on what precedes them, and on the larger rhythmic design of the period.

Koch’s pedagogy turns these principles into a method: begin with small forms, imitate clearly, and let freedom arrive after structure is understood.

The beginner should move from the simple to the complex. Instead of attempting a large composition at once, Koch recommends short pieces in which one method of phrase connection can be understood without distraction. Once that small form is secure, it can be expanded. This graded path reduces confusion, strengthens invention, and reveals how larger structures grow from manageable procedures.

Koch’s exercises rely on controlled imitation, not because originality is undesirable, but because invention needs workable forms. He rejects the romantic fantasy that genius flourishes only when freed from craft. Rules give ideas a body. Once the student has learned how phrases, cadences, and periods behave, the temporary discipline of models can fall away and become practical freedom.

Students uneasy with exact models may study them first, then attempt free imitation at the end of each chapter. The order, however, should remain: understand, imitate, then invent. Koch’s point is not obedience for its own sake, but fluency. A movement becomes a coherent composition when its phrases, cadences, proportions, and metrical stresses are shaped by craft so thoroughly that choice begins to feel natural.