In Western music, once the root note is established in our minds, our brain automatically compares all other notes played to this initial note, and tells us that we are either moving away from or towards home.

Moving away produces a sense of interest, excitement or tension. Returning home to this root note after going away produces a sense of rest, resolution or release.

Music holds our interest as long as there is a sense of motion away from the start, with the promise that we will eventually get back there again. Jerusalem has a lot of this.

The choice of words for the song was clever because everybody can relate to their sense of aspiration and group effort - which is why Jerusalem has been adopted by a wide range of people with very different beliefs.

The melody and harmony are also of great skill and subtlety. Hubert Parry, who was one of this country's most talented composers of vocal music, was able to produce a tune that emphasised Blake's words. He particularly liked the way in which the words "O clouds unfold" in the second verse coincided with one of the peaks in the melody.

Professor Jeremy Dibble, from the Department of Music at Durham University, told ICONS that the strength of Parry's choral song is its bold, noble melody - a very English trait - its spacious contours and, above all, its diatonic (in the prevailing key) and modal harmony (founded on the medieval church modes). It is the harmony that provides the wonderful atmosphere of nobility and aspiration, combined with a tinge of melancholy.

The song has key changes that underpin the melody's gradual ascent in its second half from "And did that countenance divine" that is so thrilling. Parry is also very skilful in the way the melody is so free in terms of its time signature.

The melody is actually notated in 3/2 (three beats in a bar) but this is combined with a good deal of two beats in a bar. Parry, the great composer that he was, develops these two timings throughout the song, using it with particular skill at the final climax "till we have BUILT Jerusalem."

Jerusalem's appeal is wide-ranging versions have been made by a selection of rock bands and musicians, including Billy Bragg and Fat Les!  Find out more here.