The repertoire

A symphony orchestra therefore draws most of its concerts from a core repertoire of a few dozen works, and the same names return season after season: Beethoven, Brahms, Tchaikovsky, Elgar, Sibelius, Mahler, Holst, Vaughan Williams. That is not laziness. It is arithmetic, and the arithmetic is set out below.

What an orchestra plays on a given evening, in the order it plays them, is its programme, and the shape of that list is nearly as fixed as its contents.

The anatomy of a standard programme

The standard programme has a shape so settled that players and planners refer to its parts by slot rather than by title: an opening piece, a concerto with a soloist, an interval, then a symphony. The arithmetic below is what a Saturday evening in a hall such as St David's Hall in Cardiff usually adds up to.

That comes to roughly two hours in the building. Anything that will not fit the shape has to displace it. Walton's Belshazzar's Feast, at about 35 minutes with a chorus and two extra brass bands, cannot simply be dropped into the second half without rethinking the first. Verdi's Requiem, at about 85 minutes, is the whole evening. Handel's Messiah, at about two and a quarter hours in a full performance, is the whole evening and then some.

Why the same few dozen works keep coming back

Repertoire concentrates because rehearsal time is the scarcest thing an orchestra owns. A professional orchestra prepares a standard programme in about three to four rehearsals of three hours, and considerably less on tour. Nine to twelve hours is enough to refresh a symphony the players already know and to balance a concerto against a soloist they met on Tuesday. It is not enough to learn a 45 minute score from scratch to a standard anyone would pay for. Every unfamiliar work therefore borrows time from the familiar ones sharing its programme, which is why new music usually appears in the ten minute opening slot rather than after the interval.

Size is the second constraint. A standard symphony orchestra is about 80 to 100 players in four sections, strings, woodwind, brass and percussion, and strings make up about two thirds of that number. Scores written for that establishment cost the same to stage whatever the title. Scores written for more, and Mahler and Strauss routinely ask for more, mean extra contracts, extra instrument hire and sometimes a platform extension. Scores written for less, such as a Haydn symphony, save money but do not fill a 2,000 seat hall on their own.

What a core repertoire costs a hall to abandon

Leaving the core repertoire is expensive in a way that shows up months later. Three effects compound. Subscription renewals fall, because a season of unfamiliar titles gives a subscriber no anchor to plan around. Sales at the door become unpredictable, so the finance office cannot forecast. Rehearsal costs rise, because unfamiliar music needs more hours and sometimes extra players.

The counter pressure is just as real. An orchestra that plays only the core repertoire stops commissioning, loses the composers who might have written for it, and eventually programmes a museum. Most planners resolve the tension by pairing rather than choosing: an unfamiliar piece is placed beside a title that will sell, so that the audience arrives for the Enigma Variations and hears something new in the first ten minutes. That pairing habit is the most important single thing about how a concert programme is built.

Programme or program, and the printed booklet

The word does double duty. A programme is the list of works, and it is also the printed booklet sold in the foyer that sets those works out with a note on each, which is the reason most listeners ever read a programme note at all. Programme is the British spelling and program the American, and in Britain both senses of the word take the longer form. The exception is computing, where program is standard everywhere.

The printed booklet has a format that has barely changed in a century. It carries the date and venue, the orchestra and conductor, the soloist, the list of works with composers' dates and movement titles, a programme note of a few hundred words on each work, biographies of the performers, the orchestra list naming every player, and advertising. The movement list is the part audiences use most, because it tells them when not to clap. Old programmes are collected, and several orchestras maintain a searchable database of past performances built from them.

Is orchestral music the same as classical music, and what to wear

No. Orchestral music is a scoring, meaning music written for an orchestra, while classical music is a broad tradition of written art music running from roughly 1600 to the present. Most orchestral music belongs to that tradition, but an orchestra also plays film scores, musicals, jazz arrangements and pop collaborations, and a great deal of classical music, including string quartets, piano sonatas and unaccompanied choral music, involves no orchestra at all. Used strictly, Classical with a capital C means only the period of Haydn, Mozart and early Beethoven, roughly 1750 to 1820.

On dress there is no rule and there has not been one for decades. Ordinary clothes are normal at almost every concert in Britain, including at the Welsh Proms in Cardiff each July. The orchestra dresses formally because black is neutral under stage lighting and because a uniform stops 80 to 100 individuals from becoming a distraction, not because the hall expects the same of the audience. The two conventions that do matter are arriving before the doors close, since latecomers are held outside until a break in the music, and staying silent between movements.

The shape described here is a convention, not a law, and the interesting concerts are usually the ones that break it deliberately: a programme with no concerto, a single 80 minute work, a symphony placed first. What makes those work is that the audience knows the default well enough to notice the departure.

Also in this programme

• Edward ElgarThe Enigma Variations, the Cello Concerto and the symphonies
• Ralph Vaughan WilliamsThe Tallis Fantasia, the Lark and the symphonies
• Going to a concertGoing to an orchestral concert for the first time