Playing piano with someone else is a great way to get good at musical counting. Unless you both count at the same rate and observe the note and rest values correctly, the difference will become apparent right away.
Playing well with others fosters the ability to listen and accommodate. This video of a quartet sight-reading the Schumann piano quartet Op. 47 illustrates how this works at an advanced level. The cello enters a split-second too early, causing the piano to stutter momentarily. By the third or fourth measure, all four players hear where the beat should be and synchronize their playing without stopping or starting over.
My theory on this is that musicians playing together actually synchronize heartbeats. Certainly the heartbeat is our internal metronome; we play to our heartbeat. You can check it out yourself by taking your pulse after you have been playing five minutes or so.
Playing well with others in large groups, especially orchestras, involves not only careful listening, but also a complicated kind of ranking system. The concertmaster or concertmistress sits immediately to the left of the conductor, nearest the audience, and the principal cellist sits to the conductor’s right. Each is responsible for his or her section, for synchronized bowing and fingering. Their second in command shares a music stand, away from the audience, and is responsible for turning pages or acting as principal if the principal is missing.
In the second row, the player nearest the audience outranks the player sharing his/her music stand. Woodwinds sit in the middle, behind the second violins and violas. Percussion is always at the back because of the size and unwieldiness of the instruments. Piano and harp, unless they are performing solos, generally sit in the percussion section. The brass players sit in the back rows, sometimes to the dismay of the players in front of them (though many orchestras now have plastic sound barriers in front of the brass players, to protect the hearing of the other players.)
Each section leader is responsible for his own section and usually decides the ranking of the players. The concertmaster is the president of the orchestra and works with the conductor to come to an agreement on interpretation, tempo, and other fine details.
Non-principals are called rank and file players; someone outside the group who is called in at the last minute is called a ringer.
“Keeping Score”, the fine PBS series featuring Michael Tilson Thomas and the San Francisco Symphony, shows the research, practice and experimentation which goes on before the orchestra even meets to rehearse. The symphony even employs a copyist to write all the conductor's pencilled instructions into every individual part.
Professional groups such as the Symphony hold auditions, of course, but ability is not the only thing on display at these auditions. Sometimes under a new conductor, players will be replaced because of style or temperament, no matter how well they play.
The forming of duet partners and chamber groups, whether amateur or professional, usually happens because the players like each other, have similar skill levels and musical ideas. They play well together.
