In December 1778, writing from Mannheim, where the court orchestra was perhaps the finest and most advanced in Europe, Mozart lamented to his father, "Alas, if we only had clarinets! You cannot imagine the glorious effect of a symphony with flutes, oboes, and clarinets." Though the instrument was still maturing on the technical front, Mozart quickly grasped the potential of its fluid, flexible tone, wide range, and distinctively colored registers. Beginning in 1781 with Idomeneo (written for Munich, where the Mannheim orchestra had moved with its employer), he used clarinets extensively in his operas--though less frequently in his symphonies and concertos, where the resources at hand were not always as lavish nor the players as adept.

In Vienna he was fortunate in the availability of Anton Paul Stadler (1753-1812), a member of the court orchestra beginning in 1781. Stadler was particularly noted for his mastery of the instrument's "chalumeau" register, its throaty lower register, and he himself designed a modification for the clarinet that extended it a third downwards. This mutation is now called the "basset clarinet"--and is not to be confused with the basset horn, a clarinet pitched still lower, of which Stadler was also a master.

For Stadler and his basset clarinet, Mozart in 1789 composed a miraculous quintet with strings (K. 581). Around the same time or perhaps earlier, he began a concerto for basset horn and orchestra in G major, of which only a draft of 199 measures survives. Eventually--perhaps at Stadler's instance--this became a concerto for basset clarinet, now in A major. Finished around October 7, 1791, soon after the successful opening of The Magic Flute, it was the last major work completed by Mozart. He did not hear its first performance, which Stadler gave on October 16 in Prague, where he had remained after the premiere of La Clemenza di Tito (in which he had played the virtuosic obbligato parts in Sesto's "Parto, parto" and Vitellia's "Non più di fiori").

Unfortunately, the basset clarinet failed to establish itself as a standard instrument, and when the concerto was finally published, a decade after Mozart's death, the solo part was adapted to fit the compass of the standard clarinet. In this form it became a cornerstone of the instrument's repertory, though telltale evidence of the adaptive process was perceptible in certain passages where musical logic or consistency would seem to suggest low notes available only on the basset clarinet. In the absence of the autograph score, reconstruction of the original solo part necessarily involves some conjecture; Mr. Morales's performance is based on Ernst's Hess' edition for basset clarinet.

The concerto's orchestra comprises 2 flutes, 2 bassoons, 2 horns, and strings. Not only clarinets are absent from the ensemble, but also oboes (which occupy much of the same range), and the remaining winds are generally restricted to louder orchestral passages, maintaining a framework of chamber-music intimacy. The translucence of the textures benefits Mozart's mellifluous contrapuntal episodes, while their economy gives the solo instrument ample musical space over which to display its fluency, color, and range. Thanks to the clarinet's liquid tone, even its most elaborate flourishes never cross the boundary between expressivity and display.

The Allegro's principal theme is soon restated in a quieter imitative form, and the subsequent tutti is followed by a concise closing theme. The solo exposition decorates the principal theme, introduces new material of its own, and dominates most of the development as well. Eventually, with a rising series of trills, it gives over to an orchestral tutti that touches upon less sunny regions. This in turn gracefully metamorphoses into a recapitulation, regular but elegantly tightened and refined.

The Adagio in D major, in song form (A-B-A), achieves a pensive simplicity and symmetry. In the first section, the clarinet sings two phrases, each immediately repeated by the orchestra. In the middle, its virtuosity remains subdued. The return of the A section is followed by a coda for clarinet and strings, its progress to the cadence momentarily crossed by a telling harmonic shadow. The generously proportioned Rondo, marked Allegro, arrives at a striking point of doubt and hesitation during its central episode, but the soloist gradually recovers the initial vivacity.