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Piano Concerto No. 18 in B-flat, K.456

Mozart’s sophisticated Piano Concerto No. 18 in B-flat, with its emotionally intense slow movement, was one of a string of piano concertos Mozart used as his main calling-card in becoming the most important composer in Vienna before turning his attention to opera.

Joannes Chrisostomus Wolfgang Gottlieb Mozart—who began calling himself Wolfgango Amadeo about 1770 and Wolfgang Amadè in 1777 (he used “Amadeus” only in jest)—was born in Salzburg, Austria, on January 27, 1756, and died in Vienna on December 5, 1791. He composed this concerto in Vienna and dated it September 30, 1784, in his own thematic catalogue, but we know next to nothing about its specific history.

In addition to the solo piano, the score of Mozart’s B-flat piano concerto, K.456, calls for an orchestra of just 1 flute, 2 oboes, 2 bassoons, 2 horns, and strings (first and second violins, violas, cellos, and double basses). Mozart composed two alternative first-movement cadenzas, an “Eingang” (a brief, cadenza-like “lead-in”) to be played at the fermata before the first return of the third-movement rondo theme, and a cadenza for the third movement. The concerto is about 28 minutes long.

Mozart’s B-flat piano concerto, K.456, is the fifth of eleven piano concertos Mozart wrote between February 1784, when he finished the E-flat concerto, K.449, and March 1786, when he entered into his thematic catalogue both the A major concerto, K.488, and the C minor concerto, K.491. Mozart was living in Vienna, where in the early part of 1785 he would achieve the height of his popularity as both pianist and composer, appearing regularly at the homes of the nobility and in public, and supporting himself also with a regular succession of students. On March 3, 1784, he wrote to his father Leopold that he was booked for twenty-two concerts in the space of thirty-eight days; the following fall, he played ten concerts during an eleven-day period.

Fresh from the triumph of Idomeneo—commissioned for Munich and premiered there on January 29, 1781—Mozart had arrived in Vienna on March 16 that year, summoned to that city by his employer, the Archbishop Colloredo of Salzburg, on the occasion of the Emperor Joseph II’s accession to the throne. The Archbishop’s social and financial ill-treatment of Mozart, particularly distasteful so soon after the Munich success, led rather quickly to the composer’s decision to make his own living in Vienna and his resignation from the Archbishop’s service. On July 16, 1782, the premiere at the Burgtheater of Mozart’s Die Entführung aus dem Serail (The Abduction from the Seraglio) won over the operagoing public (“Vienna refuses to hear anything else,” he wrote his father), as would Figaro four years later. The marriage to Constanze Weber, the sister of Mozart’s earlier love Aloysia Weber, took place on August 4, 1782, with only grudging approval from Leopold, and a conciliatory visit to Salzburg with Constanze the following summer didn’t especially help; but the trip back to Vienna provided the occasion for Mozart’s writing the Linz Symphony when a concert was arranged there in his honor and he didn’t have an appropriate work at hand.

In February 1785, Leopold was visiting Mozart in Vienna, where he was able to witness firsthand the evidence of his son’s success; and it certainly did not hurt to hear Haydn’s comment, “Before God and as an honest man I tell you that your son is the greatest composer known to me either in person or by name”—this on the occasion of a read-through of several string quartets newly completed and dedicated by Mozart to the older composer. The next night, as he reported in a letter dated February 16 to Wolfgang’s sister Nannerl in Salzburg, Leopold attended a concert at which he heard his son perform “a glorious concerto, which he composed for the Paradis to [‘nach’] Paris,” and which moved Leopold to tears for “hearing so clearly all the interplay of the instruments.” For a long while this was believed to be the present B-flat concerto, K.456, but this has never been corroborated. (Maria Theresia von Paradis [1759-1824] was a blind pianist, organist, composer, and singer. A special system of musical “notation” was invented for her whereby differently shaped pegs stuck into a board helped her distinguish the pitch and duration of notes.) So apart from Mozart’s catalogue-entry date of September 30, 1784, we have only the music of this very beautiful, restrained, and heartfelt work to tell us anything at all—which is, of course, a great deal.

Like the Piano Concerto No. 15, K.450, which preceded it by half a year, and like Mozart’s last work in the genre, the contemplative K.595, completed in 1791, his final year, the present concerto is in the warmly relaxed key of B-flat. K.456 opens with a march-like theme whose successive phrases make immediately apparent just how central is the alternation of winds and strings to Mozart’s conception. The second theme is readily identifiable, beginning with a turn figure in thirds, exploiting the reedy sound of oboes. But even more important are the relatively brief materials that precede and follow this theme, the first skewing gently syncopated winds against a cushion of strings, the second lyrically canonic and gently breathed.

Both of these ideas are extraordinary for their sense of space and their ease of expression, aspects upon which the soloist can embellish and broadly expand at the corresponding points in the second exposition, the one in which the piano enters to join the orchestra. The piano is given its own new theme at the very beginning of the development, but the moments to listen for as this movement continues must also include the three-measure, stop-motion woodwind assertion that leads to the recapitulation, and the way in which the orchestra reclaims our attention following the soloist’s cadenza.

An aura of melancholy pervades the Andante; Mozart commentator Cuthbert Girdlestone (1895-1975) observed that its theme “expresses despair carried almost to a point of physical suffering, but without agitation, without a hint of rebellion.” The key is G minor, the relative minor of B-flat, but the immediate and emphatic change of mood at once suggests a key more distantly removed from the opening Allegro. Mozart writes a theme with variations—for him a somewhat unusual procedure—and perhaps it is the basically non-developmental aspect of this form that contributes to the sense of resignation hinted at by Girdlestone. Again the contrast between strings and winds is a primary concern, but here the unaccompanied piano also plays an important part as the movement proceeds.

The Andante’s central variation is densely scored, combined winds and strings contrasting strongly with the soloist’s phrases. The fourth variation is in the major mode but gives way once more to the minor for the last variation, in which the piano emphasizes high-register octaves, the only way it can make itself heard against the plaintive cries of the full orchestra. The final pages are stark, and even more startling in their extraordinary (again) use of dissonance than what has preceded, so that even a short-lived attempt on the soloist’s part to summon back G major remains futile in its effort to alleviate the pain and insecurity of the closing measures.

Aside from an agitated central episode that takes B minor as its starting point and whose mood argues successfully against an expected return of the 6/8 hunting theme, the rondo finale is elegant, good-natured, and generally well-behaved. Yet this movement is at the same time engagingly lively, and Mozart’s wonderful sense of humor keeps surfacing to remind us that, for a while at least, the tribulations of the Andante are past.

Marc Mandel

Marc Mandel joined the staff of the Boston Symphony Orchestra in 1978 and managed the BSO’s program book from 1979 until his retirement as Director of Program Publications in 2020.

The first Boston Symphony performances of Mozart’s Piano Concerto No. 18 in B-flat, K.456, featured Lili Kraus with Pierre Monteux conducting on April 10 and 11, 1953.