During the early years of the Romantic era the piano sonata retained its popularity, along with sonatas for violin or cello and piano. As the century progressed the symphony became the most important composite instrumental form. Composers enriched its sonorities and combined it with literary ideas because of its new sonorous possibilities for realism. There was greater contrast among the the themes of the Romantic symphony than in the Classic, especially contrast between a vigorous first theme or theme group and a more lyric second theme or theme group. Modulations were more varied, often without the usual preparation. Because there was less emphasis on balance and logic, a more sectional scheme of organization resulted. Unity among movements was often achieved by the cyclic principle; that is, using the same themes, or portions of them, in each movement. While the emphasis in the Classic sonata or symphony was on the first movement, the Romantic symphony often placed its emphasis on the last movement. This is especially true when such works were cast in cyclic form in which the climax, or culmination of the thematic material, occurred during the last movement. A number of composers included solo and choral writing in their symphonies in the desire to emphasize the climax of the last movement. The minuet was usually replaced by a scherzo, a movement quicker in tempo that provided more contrast to the second and last movements. The variation form was frequently used as either the second or last movement. Some composers used five movements in their symphonies, in contrast with the usual four-movement Classic symphony.