Importance was given to instrumental music. It was dominated by further development of musical forms initially defined in the Baroque period: the sonata, the concerto, and the symphony. Others main kinds were the trio, string quartet, serenade and divertimento. The sonata was the most important and developed form. Although Baroque composers also wrote sonatas, the Classical style of sonata is completely distinct. All of the main instrumental forms of the Classical era, from string quartets to symphonies and concertos, were based on the structure of the sonata. The instruments used chamber music and orchestra became more standardized. In place of the basso continuo group of the Baroque era, which consisted of harpsichord, organ or lute along with a number of bass instruments selected at the discretion of the group leader (e.g., viol, cello, theorbo, serpent), Classical chamber groups used specified, standardized instruments (e.g., a string quartet would be performed by two violins, a viola and a cello). The Baroque era improvised chord-playing of the continuo keyboardist or lute player was gradually phased out between 1750 and 1800.