In
diatonic harmony and
tonal music, certain
scale degrees have an
aural tendency to "want to go" to other scale degrees.
The strongest tendency tone is the 7th scale degree or "
leading tone". It exhibits an unusually strong tendency to "go to" or resolve to the 1st scale degree, or "
tonic". This is why, in
pop music or church
chorales and
hymns, when you hear a V7 chord it makes sense and even relaxes your ear when it goes back to the
chord the whole thing started in. 7 goes to 1, and your ear will always want to hear it go to 1, especially if it is sustained.
The other strong tendency in tonal music for 4 (
subdominant) to resolve down to 3 (
mediant). This happens often enough but not with the regularity that 7 moves to 1.
The major exception concerning the 7->1 movement is when the
melody descends from 1 in a
conjunct motion, 1->7->6->5, as in the first four notes of "
Joy to the World".