A hymnal or hymnary is a collection of hymns, usually in the form of a book, called a hymnbook (or hymn book). Hymnals are used in congregational singing. A hymnal may contain only hymn texts (normal for most hymnals for most centuries of Christian history); written melodies are extra, and more recently harmony parts have also been provided. Hymnals are omnipresent in churches but they are not often discussed; nevertheless, liturgical scholar Massey H. Shepherd once observed: "in all periods of the Church’s history, the theology of the people has been chiefly molded by their hymns."