Teachers typically assign the student pieces (or songs for vocal students) of slowly increasing difficulty. Besides using pieces to teach various musical rudiments (rhythm, harmony, pitch, etc.) and teach the elements of good playing (or singing) style, a good teacher also inspires more intangible qualities such as expressiveness and musicianship. Pieces (or songs) are more enjoyable for most students than theory or scale exercises, and an emphasis on learning new pieces is usually required to maintain students' motivation. However, the teacher must not over-accommodate a student's desire for "fun" pieces. Often the student's idea of fun music is popular vocal selections, movie soundtracks, and TV show theme songs, etc. While some of these "fun" pieces can be performed, pieces should also be selected for pedagogical reasons, such as challenging the student and honing their skills. Student should learn something from every piece they play. In addition, for students to be well rounded they must play many types of pieces by composers and songwriters from different eras, ranging from Renaissance music to pieces from the 20th and 21st century. A varied repertoire increases the student's musical understanding and skill.