Clementi is best known for his collection of piano studies, Gradus ad Parnassum, to which Debussy's piece "Doctor Gradus ad Parnassum" (the first movement of his suite Children's Corner) makes playful allusion. Similarly his sonatinas would remain a must for piano students everywhere, until late 20th century. Erik Satie, a contemporary of Debussy, would spoof these sonatinas (specifically the sonatina Op. 36 N° 1) in his Sonatine Bureaucratique.
Wolfgang Amadeus Mozart held an inexplicable dislike for Clementi (and perhaps Italians in general), which has led some to call them "arch rivals." However, this distinction would not be correct, because Clementi himself does not seem to have reciprocated Mozart's feelings.
The pianist Vladimir Horowitz developed a special fondness for Clementi's work, comparing some of them to the best works of Beethoven. The restoration of Clementi's image as an artist to be taken seriously is not least due to his efforts.
Muzio Clementi is a highly underregarded figure in the music world. He is widely regarded by scholars as the creator of both the modern pianoforte as an instrument, and the father of modern piano-playing. But first things first: Muzio was born in Rome in 1752, the first of seven children, to Nicolò Clementi, a highly respected silversmith and Roman by heritage, and Magdalena Kaiser, who was Swiss. His musical talent became clear at an early age: by age seven he was in musical instruction, and was such a good student that by age 13 he gained a position as a church organist.
In 1766, Sir Peter Beckford (1740-1811), a wealthy Englishman and cousin of the eccentric William Beckford, took an interest in the boy's musical talent, and struck a deal with Nicolò to take Clementi to his estate of Steepleton Iwerne, just north of Blandford Forum in Dorset, England - where Beckford agreed to provide quarterly payments to sponsor Clementi's musical education. In return for this education, Clementi was expected to provide musical entertainment at the estate. It was here that Clementi spent the next seven years in devoted study and practice at the harpsichord. His compositions from this early period, however, are few, and they've almost all been lost.
In 1770, Clementi made his first public performance as a pianist. The audience was very impressed with his playing, beginning what at the time was one of the most successful concert pianist careers in history. In 1774, Clementi was freed from his obligations to Peter Beckford, and he moved to London, where among other accomplishments he made several public appearances as a solo harpsichordist at benefit concerts for a singer and a harpist, and served as "conductor" - from the keyboard! - at the King's Theatre, Haymarket for at least part of this period. His popularity grew in 1779 and 1780, due at least in part to the popularity of his newly-published Opus 2 Sonatas. His fame and popularity rose quickly, and he was considered by many in musical circles to be the greatest piano virtuoso in the world.
Clementi started a European tour in 1781, when he travelled to France, Germany, and Austria. In Vindabona, Clementi agreed with Emperor Josef II to enter a musical duel with Wolfgang Amadeus Mozart for the entertainment of the Emperor and his guests. Each performer was called upon to improvise and perform selections from his own compositions. The ability of both these composers and virtuosi was so great that the Emperor was forced to declare a tie.
On January 12, 1782, Mozart wrote to his father: "Clementi plays well, as far as execution with the right hand goes. His greatest strength lies in his passages in 3rds. Apart from that, he has not a kreuzer's worth of taste or feeling - in short he is a mere mechanicus". In a subsequent letter, he even went so far as to say "Clementi is a charlatan, like all Italians." Clementi's impressions of Mozart, by contrast, were all rather enthusiastically positive.
But the main theme of Clementi's B-Flat Major sonata captured Mozart's imagination, and ten years later he used it the overture to his opera Die Zauberflöte (The Magic Flute). This so embittered Clementi that every time this sonata was published, he made certain that it included a note explaining that it had been written ten years before Mozart began writing Die Zauberflöte.
Starting in 1782, and for the next twenty years Clementi stayed in England playing the piano, conducting, and teaching. Two of his students attained a fair amount of fame for themselves: J.B. Cramer and John Field (who, in his turn, would become a major influence to Frederic Chopin). Clementi also began manufacturing pianos, but in 1807 his factory was destroyed by a fire. That same year, Clementi struck a deal with Ludwig van Beethoven, one of his greatest admirers, that gave him full publishing rights to all of Beethoven's music. His stature in music history as an editor and interpreter of Beethoven's music is certainly not less than as being a composer himself (although also criticised for some less docile editorial work, e.g. making harmonic "corrections" to some of Beethoven's music). That Beethoven in his later life started to compose (mostly chamber music) specifically for the British market might have been related to the fact that his publisher was based there. In 1810 Clementi ceased his concerts to devote all of his time to composition and piano making. In 1830 he moved to live outside Lichfield and then spent his final, less exciting years in Evesham, where he died 80 years old. He was buried at Westminster Abbey. He had been married three times.
Clementi composed almost 110 piano sonatas (most of them sonatinas), many of which are still played and many are popular practice pieces in piano education. His sonatas are only very rarely performed in public concerts, largely because they are seen as nonchallenging educational music. Clementi's sonatas are often more difficult to play than Mozart's, though - Mozart, in fact, wrote in a letter to his sister that he would prefer she not play the Clementi's sonatas due to their jumped runs, wide fingerspacing, and chords that he thought would cause injury for her to try to play.
In addition to the piano solo stuff, Clementi wrote a great deal of other music, including several recently pieced together, long worked on but slightly unfinished symphonies that are gradually becoming accepted by the musical establishment as being very fine works. While Clementi's music is hardly ever played in concerts, it is becoming increasingly popular in recordings.
Being a contemporary of the greatest classical piano composers (Mozart, Beethoven,...) cast a large shadow on his own work (making him one of the "lesser gods"), at least in concert practice, despite the fact that he had a central position in the history of piano music, and in the development of the sonata form.