"I'm going to sound like I really hate singers, but I do think there's too many women vocalists out there right now." This comment, from the Dutch drummer Sebastian de Krom, breaks the omerta that lies like an invisible veil over so many in the jazz world. Reservations may be muttered privately, but rarely are they voiced in public. All must be celebrated, and that includes singers, of whom there seems to be an inexhaustible supply ready to tread the well-worn path on which they expect the grateful listener to cast palms before their feet.

There is a school of thought, for which I have some sympathy, that there is actually no such thing as a jazz singer, only singers who perform material from within the jazz repertoire. The late Benny Green was particularly (and typically) forceful on this subject. "The sincerity of these singers is of course unimpeachable," he said, "but then so was Genghis Khan's, and they remain a band of brave but deluded pilgrims marching resolutely in the wrong direction."

The main reason for excluding singers is that most of them lack one of the key attributes of a jazz musician: the ability to improvise. That also applies to a few who do attempt brief essays into doobie-doo-land only to demonstrate such a rudimentary grasp of harmony and intonation that they deserve medals for aural effrontery. But leaving aside such efforts, which would best be launched alone and in the bathtub, the singer whose contribution is to top and tail a saxophone or piano solo with an exposition of a melody cannot really be said to have done anything meriting the label "jazz". As Ron Carter, that most impeccable and distinguished of double bassists, puts it: singers "bring nothing else to the table".

Those like Mark Murphy and Dee Dee Bridgewater who are accomplished scat singers, or the vocalese experts Jon Hendricks and Eddie Jefferson, are rightful bearers of the title "jazz singer". Capable of sustaining solos of equal complexity and interest to any horn player, they use their voices as instruments and bring something very different to the table.

No one (apart from Green) would deny vocalists of the stature of Tony Bennett and Billie Holiday a place in the pantheon. Their sensibility and interpretation of a lyric earns them their inclusion, although only on the level of Eros and the other demi-gods. Armstrong, Ellington, Parker and Davis remain the Cronos, Zeus et al of this world. For although in the popular perception vocalists are a key part of the music, along with smoky clubs, Zoot suits and every other cliché you can pick out of the bag, it's hard to think of one singer who has made any significant contribution to the development of jazz. To concentrate on them is to be side-tracked, often gloriously and wonderfully so, but nevertheless side-tracked.

This is not to say that we should ignore the ornaments of this profession. The world would be a poorer place without Claire Martin, Norma Winstone or Cleo Laine. But the real meat of jazz is cooked by the instrumentalists, and de Krom's comments should be born in mind by those tempted to ice the cake with yet another rendition of "Bewitched, Bothered and Bewildered". If you can't bring anything new to the baking, stay out of the kitchen.