Renaissance music is traditionally understood to cover European music of the 15th and 16th centuries, later than the Renaissance era as it is understood in other disciplines. Rather than starting from the early 14th-century ars nova, the Trecento music was treated by musicology as a coda to Medieval music and the new era dated from the rise of triadic harmony and the spread of the ' contenance angloise ' style from Britain to the Burgundian School. A convenient watershed for its end is the adoption of basso continuo at the beginning of the Baroque period. The period may be roughly subdivided, with an early period corresponding to the career of Guillaume Du Fay (c. 1397–1474) and the cultivation of cantilena style, a middle dominated by Franco-Flemish School and the four-part textures favored by Johannes Ockeghem (1410s or '20s–1497) and Josquin des Prez (late 1450s–1521), and culminating during the Counter-Reformation in the florid counterpoint of Palestrina (c. 1525–1594) and the Roman School. Music was increasingly freed from medieval constraints, and more variety was permitted in range, rhythm, harmony, form, and notation. On the other hand, rules of counterpoint became more constrained, particularly with regard to treatment of dissonances. In the Renaissance, music became a vehicle for personal expression. Composers found ways to make vocal music more expressive of the texts they were setting. Secular music absorbed techniques from sacred music, and vice versa. Popular secular forms such as the chanson and madrigal spread throughout Europe. Courts employed virtuoso performers, both singers and instrumentalists. Music also became more self-sufficient with its availability in printed form, existing for its own sake. Precursor versions of many familiar modern instruments (including the violin, guitar, lute and keyboard instruments) developed into new forms during the Renaissance. These instruments were modified to respond to the evolution of musical ideas, and they presented new possibilities for composers and musicians to explore. Early forms of modern woodwind and brass instruments like the bassoon and trombone also appeared, extending the range of sonic color and increasing the sound of instrumental ensembles. During the 15th century, the sound of full triads became common, and towards the end of the 16th century the system of church modes began to break down entirely, giving way to functional tonality (the system in which songs and pieces are based on musical "keys"), which would dominate Western art music for the next three centuries. From the