 For example, if the piece is in C minor, the first and second horns might be in C, the tonic major key, which could get most of the notes, and the third and fourth horns might be in E, the relative major key, to fill in the gaps.Many orchestral horn sections in the 2010s also have an assistant who doubles the first horn part for selected passages, joining in loud parts, playing instead of the principal if there is a first horn solo approaching, or alternating with the principal if the part is tiring to play.Often the assistant is asked to play a passage after resting a long time.