The texts of many hymns were written without a particular tune in mind. Some hymn texts began as poetry intended to be spoken or read, and later were discovered to be suitable for singing. So composers, church musicians, or hymnal editors assigned a new or traditional tune to the text (or, more commonly, assigned the text to a pre-existing tune).
For convenience sake, tunes have been given names by musicians and editors, or (more rarely) a name has been selected by the composer of the tune. When tune and text are by the same person (e.g., Martin Luther’s “A Mighty Fortress”), the tune name is clearly associated with the text. The first three words of “A Mighty Fortress” in the original German are “Ein’ feste Burg,” which for centuries has been the name of the tune. Tune names are conventionally displayed in small caps, so hymnals will identify this tune as EIN’ FESTE BURG.
Most texts can be sung to different tunes, and many tunes are suitable for multiple texts. In our Hymnal, for example, “Rock of ages” (#471) is set to two very different tunes. In our Hymnal, the first tune presented is called PETRA (more on this tune below). On the next page of the Hymnal, “Rock of Ages” is printed to the tune TOPLADY. That name was bestowed in honor of the name of the poet who wrote the text to “Rock of Ages,” Augustus Montague Toplady.
To digress away from the conventions of naming for a minute, note how the tunes differ significantly in mood. PETRA is in 4/4 time, with a steady pulse of quarter notes. It is the more somber of the tunes. If PETRA feels like a quiet processional (see below), TOPLADY alternates between lullaby and dramatic lament (the first four notes are the same as those in “Silent Night,” a Christmas lullaby). It is in triple meter (3 beats to each measure) and has obvious emotional intensity. Most of the notes are in the higher half of the hymn’s range, and the leap from the second syllable of “ages” to the higher (and slightly longer) note on “cleft” has the feel of an impassioned cry. There are good reasons why this melody is more associated with the revivalist tradition than is PETRA.
Back to tune names. PETRA is something of an alias for this tune. (Yes, it’s confusing: the same tune might show up with a different name. There is no authoritative international body assigning these labels.) The most common name for this tune is REDHEAD NO. 76, which to me suggests either a formula for a shampoo or one in a long string of interchangeable girlfriends. It actually refers to the composer of the tune, Richard Redhead (1820-1901). A much better name is PETRA, which the tune acquired with its association with “Rock of Ages.” The tune is also sometimes known as GETHSEMANE, because it is used (as in our Hymnal, #70) to sing the Passiontide hymn “Go to dark Gethsemene,” which we often use as a processional hymn on Maundy Thursday.
Our Hymnal has an Index of Tunes beginning on page 819. You can learn a lot more about the history and use of specific hymn tunes (and much else about hymns) at hymnary.org.