Brahms’ chromatic innovation, WoO 25
The four-voice, posthumously published modulating canon "Mir lächelt kein Frühling" by Johannes Brahms is much like a round, but each new entry enters a melancholy semitone lower than the last. Once all the voices have entered and as each of these voices makes its way through the 16-measure melody, what we hear is a four-measure unit or iteration descending each time by semitone. By the time the dux repeats, it is a full ditone (or major third) lower than before. To the composer, aside from the task of accomplishing the modulation, the challenge of the canon is the same as that of a canon at the unison; invertible counterpoint is not a requirement.
Due to the composer's skill at modulation, the effect is however not of a blatant shift downward with each iteration, but a subtle one without any discernible point of downward chromatic shift.
Yes, each iteration is in a different key, but the fact that the successively descending iterations are otherwise identical also makes the canon easier to analyze.
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What makes this canon most remarkable is the success of the modulation. That is to say, the modulation is convincingly deceptive, especially for such a brief one and such a distant one. Brahms uses the indispensable technique of subtle modulation using a pivot.
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It can be seen from the graphic depiction above (download to enlarge) that once all voices have entered, each four-measure iteration of the canon is the same, keeping in mind that the canon modulates, so that each iteration is also a semitone lower than the previous iteration.
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How does Brahms make the modulation convincing?
One subtle detail that helps the modulation is a chromatic line that uses the technique of hocket, where a melody is transferred from one voice to another as it progresses. In measure 15, the dux (voice 1) repeats the notes D-flat, C, then leaps down below the next chromatic note B-natural, singing instead the note F, while voice 4 sings the B, now a leading tone to C in a fully-diminished harmony.
When the ear listens to a diminished-seventh chord, it is the notes outside the chord that orient the listener as to the key or expected chord of resolution. In the vacillation between B and C those notes can be heard as leading-tone and tonic, but they can also be heard as dominant and minor submediant, and the latter interpretation is corroborated in measure 17 as F-sharp appears in the dux, soon followed by the new leading tone, D-sharp in voice 3. The modulation is handled craftily, as any sort of F is avoided following the downbeat of measure 16, where the lower tones E and G sound as the third and fifth of an inverted C-major triad—a tonic in the new key of C, but a weak submediant chord in the key of E minor. Brahms takes advantage of this weakness, the tendency for a first-inversion submediant triad to sound like a watered-down tonic triad, and simply makes it so, as the upper note C finally resolves down by step to B, the fifth of the E-minor triad.
The avoidance of either F or F-sharp (and any other note that might contradict either a tonality of C or of E, would spoil the pivot, which is maintained from measure 16, beat 2 through measure 17, beat 2. After this hiatus known as the pivot, the ear accepts the F-sharp and D-sharp and contextualizes the entire harmonic environment as the realm of E minor.
Moreover, in measure 17, the E-minor triad is approached in a way that sounds somewhat native to its key—at least after the downbeat of measure 16. Now all that remains is to confirm the new key of E minor with a clear and decisive dominant-to-tonic resolution. This happens twice over the course of measures 17 and 18, just precisely as it did in the key of F minor four measures earlier.
If you were not sure how this happened as you were hearing it, the four-measure iteration will be replaced by another, and although invertible counterpoint is not used to vary the iterations, the mere fact of their modulation does provide a sense of new flavor with each iteration.
A choral performance by Chor des Norddeutschen Rundfunks can be found on youtube.