“Hymns” as we see them in hymnbooks are not written for the organ, nor for the piano, but for the human voice. Some hymns, like the example to the right, are intended for unison voices. These usually include an accompaniment composed especially for the organ or for the piano.
Most hymns, however, are composed for four voice parts: soprano, alto, tenor, and bass. Since they were conceived for vocal performance, many hymns as they appear in hymnbooks do not sound well when played on the organ exactly as written. For this reason, musically convincing hymn playing at the organ usually requires that the vocal score be modified.