See A. C. Boult, A Handbook on the Technique of Conducting (7th ed. 1951); C. Bamberger, The Conductor's Art (1965); H. C. Schonberg, The Great Conductors (1967).
In the 17th century, other devices to indicate the passing of time came into use. Rolled up sheets of paper, smaller sticks and unadorned hands are all shown in pictures from this period. The large staff was responsible for the death of Jean-Baptiste Lully, who stabbed his foot with one while conducting a Te Deum for the king's recovery from illness. The wound became gangrenous, and despite the efforts of doctors the gangrene spread to his leg and he died two months later.
In instrumental music, a member of the ensemble usually acted as the conductor. This was sometimes the principal violinist, who could use his bow as a baton, or a lutenist who would move the neck of his instrument in time with the beat. It was common to conduct from the harpsichord in pieces that had a basso continuo part. In opera performances, there were sometimes two conductors - the keyboard player was in charge of the singers, and the principal violinist was in charge of the orchestra.
By the early 19th century, it became the norm to have a dedicated conductor, who did not also play an instrument during the performance. The size of the usual orchestra expanded during this period, and the use of a baton became more common, as it was easier to see than bare hands or rolled-up paper. Among the earliest notable conductors were Louis Spohr, Carl Maria von Weber, Louis Antoine Jullien and Felix Mendelssohn, all of whom were also composers. Mendelssohn is claimed to have been the first conductor to utilize a wooden baton to keep time, a practice still generally in use today. Amongst prominent conductors who did not or do not use a baton are Leopold Stokowski, Pierre Boulez, Dimitri Mitropoulos and Kurt Masur . Hans von Bülow is commonly considered the first professional musician whose principal career was as a conductor.
Hector Berlioz and Richard Wagner were also conductors, and they wrote two of the earliest essays dedicated to the subject. Berlioz is considered the first virtuoso conductor. Wagner was largely responsible for shaping the conductor's role as one who imposes his own view of a piece onto the performance rather than one who is simply responsible for ensuring entries are made at the right time and that there is a unified beat.
In the late 20th century, a New York composer Walter Thompson created a live composing sign language known as soundpainting to be used in the medium of structured improvisation. At present the language includes over 750 gestures used as communication tool by the composer/conductor to indicate the type of improvisation desired of the performers. In addition, a system called conduction, developed by Lawrence D. "Butch" Morris, is another prominent movement in the field. The latter is considered more effective to dictate relationships and transformations, giving the improvisers more control over the content they contribute.
An understanding of the basic elements of musical expression (tempo, dynamics, articulation) and the ability to communicate them effectively to an ensemble is necessary in order to conduct. The ability to communicate nuances of phrasing and expression through gesture is also beneficial. Conducting gestures may be choreographed beforehand by the conductor while studying the score, or may be spontaneous.
A distinction is sometimes made between orchestral conducting and choral conducting. Stereotypically, orchestral conductors use a baton more often than choral conductors (though not always: this is up to the conductor's personal preference), and favor the use of beat patterns over gestural conducting, which concentrates more on musical expression and shape.
The grip of the baton varies from conductor to conductor. Despite a wide variety of styles, a number of standard conventions have developed.
The beat of the music is typically indicated with the conductor's right hand, with or without a baton. The hand traces a shape in the air in every bar (measure) depending on the time signature, indicating each beat with a change from downward to upward motion. The images show the most common beat patterns, as seen from the conductor's point of view.
The downbeat indicates the first beat of the bar, and the upbeat indicates the last beat of the bar. The instant at which the beat occurs is called the ictus (plural: ictus or ictuses), and is usually indicated by a sudden (though not necessarily large) click of the wrist or change in baton direction. In some instances, "ictus" is also used to refer to a horizontal plane in which all the ictuses are physically located, such as the top of a music stand where a baton is tapped at each ictus. The gesture leading up to the ictus is called the "preparation", and the continuous flow of steady beats is called the "takt".
If the tempo is slow or slowing, or if the time signature is compound, a conductor will sometimes indicate "subdivisions" of the beats. The conductor can do this by adding a smaller movement in the same direction as the movement for the beat that it belongs to.
Changes to the tempo are indicated by changing the speed of the beat. To carry out and to control a rallentando, a conductor may introduce beat subdivisions.
Some conductors use both hands to indicate the beat, with the left hand mirroring the right, though others view this as redundant and therefore to be avoided. This is also seen as improper practice by many. The second hand may be used for cueing the entrances of individual players or sections, and to aid indications of dynamics, phrasing, expression, and other elements.
Dynamics can be fine-tuned using various gestures: showing one's palm to the performers or leaning away from them may demonstrate a decrease in volume. In order to adjust the overall balance of the various instruments or voices, these signals can be combined or directed towards a particular section or performer.
Phrasing may be indicated by wide overhead arcs or by a smooth hand motion either forwards or side-to-side. A held note is often indicated by a hand held flat with palm up. The end of a note, called a "cutoff" or "release", may be indicated by a circular motion, the closing of the palm, or the pinching of finger and thumb. A release is usually preceded by a preparation and concluded with a complete stillness.
Conductors aim to maintain eye contact with the ensemble as much as possible, encouraging eye contact in return and increasing the dialogue between players/singers and conductor. Facial expressions may also be important to demonstrate the character of the music or to encourage the players.