No other cellist had such an influence on cello playing in the 20th century codice_1. He changed the way people thought about cello technique. For example: when he was young violinists and cellists were taught to practise with a book under the right arm. This made the bowing arm very stiff. Casals taught his pupils to play with a free bowing arm. Casals was a great teacher, and he learned a lot about playing through his teaching. He thought about fingering and bowing, and showed his pupils how their left hand could be strong but also relaxed.