Curse of the ninth

The curse of the ninth is a superstition connected with the history of classical music. In essence, it is the belief that a ninth symphony is destined to be a composer's last; "i.e." that the composer will be fated to die while or after writing it, or before completing a tenth. To those who give credence to the notion, a composer who produces a ninth symphony has reached a decisive landmark, and to then embark on a tenth is a challenge to fate.
This folk-notion persists in popular journalism, and is not supported in musicology or "serious" music criticism. Though composers can indeed be found who died after achieving nine symphonies (the most famous example being Ludwig van Beethoven), nine is not a statistically predominant total in the history of the symphony. In addition, while some very prominent composers (e.g. Schubert, Dvořák, Spohr, Bruckner, Mahler, and Vaughan Williams) are regularly adduced as examples, several of them are only credited with having "composed nine symphonies" as a result of error or oversimplification.
Beginnings.
According to Arnold Schoenberg, this superstition began with Gustav Mahler, who, after writing his Eighth Symphony, wrote "Das Lied von der Erde", which, while structurally a symphony, was able to be disguised as a song cycle, each movement being a setting of a poem for soloist and orchestra. Then he wrote his Ninth Symphony and thought he had beaten the curse, but died with his Tenth Symphony incomplete.
In an essay about Mahler, Schoenberg wrote: "It seems that the Ninth is a limit. He who wants to go beyond it must pass away. It seems as if something might be imparted to us in the Tenth which we ought not yet to know, for which we are not ready. Those who have written a Ninth stood too close to the hereafter."
The difficulties with this analysis are obvious. From Mahler's point of view, the only important victim of any "curse of the ninth" (Mahler is not known to have used the term) would have been Ludwig van Beethoven. Even Anton Bruckner (with whom Mahler had been closely associated) fails to qualify: Bruckner died "before completing" the work that is now played as his (unfinished) "Ninth Symphony", with the result that his symphonic total is eight if only the completed canonical works are counted – and ten if the list includes the early Study Symphony in F minor and the D minor Symphony now known as "No. 0" – both of them withdrawn by the composer. Bruckner was in fact superstitious about his own Ninth Symphony; but this was not because of any belief in a "curse of the ninth", but because it was in the same key as Beethoven's Ninth.
Franz Schubert's inclusion in any list is similarly problematic. Mahler would not even have considered Schubert to have written nine symphonies, as the "Great" C major Symphony was reckoned as "No. 7" in Mahler's time. And while that symphony is now numbered as a ninth (and was followed by a tenth that remained uncompleted in piano score), this reckoning includes the Unfinished Symphony (now numbered as the 8th), and a "seventh symphony" that never progressed beyond an incompletely filled-in full score. Drawing on these materials, orchestrations have been realized of both symphonies. The tenth, in particular, was the last piece Schubert was working on before his death, and the piano sketch is close to complete. Brian Newbould (as well as Pierre Batholomée, and Luciano Berio) finalized and published an orchestral realization and recorded performances suggest anticipations of Bruckner and Mahler. Similarly, composed in 1821, Schubert's draft for his seventh symphony is considered to be structurally complete, but Schubert orchestrated only part of it. Drawing on Schubert's material, orchestrations have been completed by John Francis Barnett (1881), Felix Weingartner (1934) and Brian Newbould (1980). 
Similarly, Antonín Dvořák's "New World" Symphony would not have been considered a "ninth" in Mahler's time, as the work was published as "No. 5", with four of Dvořák's earlier symphonies appearing only after his death. The situation is further complicated by the fact that Dvořák considered the score of his early C minor symphony to be lost (it only resurfaced nearly two decades after his death, and had to wait a further 13 years for its first performance). Still another case is that of Louis Spohr, who wrote and completed a tenth symphony and then withdrew it.
Others.
After Mahler, some composers used as examples of the curse include: Kurt Atterberg, David Maslanka, Vincent Persichetti, Alfred Schnittke, Roger Sessions and Elie Siegmeister. However, many of these examples have elements which tend to work against the superstition: Schnittke wrote his Ninth and last symphony with his left hand while virtually paralysed and unable to speak from a series of strokes; the authenticity of the work finally performed as an interpretation of his manuscript is problematic. In any case a "Symphony No. 0" by Schnittke has been performed and recorded, so his total should be ten. Alexander Glazunov completed the first movement of his Ninth but worked on it no further for the 26 more years he lived. In an interview recorded at the time of its premiere, Malcolm Arnold stated that he intended his Ninth Symphony (his op. 128) to be his last; it proved to be so, but he was to live for another twenty years, reaching opus 142. Hans Huber has eight numbered symphonies, along with one assigned as "No. 2" and premiered but later withdrawn. Jean Sibelius is not usually cited as an example, although if one were to count "Kullervo" as his first symphony, the ill-fated Eighth was the ninth he worked on. There is evidence from his correspondence with George Butterworth that Ralph Vaughan Williams did not regard his choral cantata "A Sea Symphony" (1910) as a true symphony and considered his 1913 "A London Symphony" as his first work in the genre. However, he did not number his symphonies until 1956 when his "Symphony in D minor" appeared. Concerned that the work might be confused with his "Symphony in D" (1943), his publisher suggested the new work should be called number 8, since by that time "A Sea Symphony" had not been generally accepted as Vaughan Williams's first symphony, so that when his last symphony appeared in 1958, the year of his death, it was counted as number 9.
Counterexamples.
Numerous composers after Beethoven have composed more than 9 symphonies. Those who violated the "curse of the ninth" include Andrzej Panufnik (10), Peter Maxwell Davies (10), Hans Werner Henze (10), Eduard Tubin (10), William Schuman (10; his first two were withdrawn), Alun Hoddinott (10), David Diamond (11), Joachim Raff (11), Edmund Rubbra (11), Robert Simpson (11), Philip Glass (12, ), Heitor Villa-Lobos (12, although Symphony No. 5 is lost), Darius Milhaud and Alexander Moyzes (12 each, plus 6 chamber symphonies in Milhaud's case), Vagn Holmboe (13, plus chamber symphonies and symphonies for strings), Roy Harris (13), Gloria Coates (16, ), Dmitri Shostakovich (15), Rued Langgaard (16), Allan Pettersson (16), Gian Francesco Malipiero (17), Kalevi Aho (17, plus 3 chamber symphonies, ), Boris Tishchenko (18: 9 unnumbered and 9 numbered, No. 9 unfinished) Henry Cowell (20), Lev Knipper (20), Jānis Ivanovs (20), Mieczysław Weinberg (22), Nikolai Myaskovsky (27), Havergal Brian (32), Sergei Slonimsky (34), Alan Hovhaness (67), Derek Bourgeois (116), and Leif Segerstam (343 )
Composers before Beethoven, such as Joseph Haydn (106), Michael Haydn (41), and Wolfgang Amadeus Mozart (around 50), are not considered relevant to this superstition.