I grew up seeing shape notes frequently. The Christian Hymnal at Upper Skippack Mennonite Church, also known as the black hymnal due to its dark cover, contained shapely notes. Yet I never learned to read shape notes. The music theory I learned involved key signatures and round notes organized on a staff.
Recently I recalled shape notes and it bothered me that I did not know how to read them. So I did some research.
It seems shape notes are the mercenaries of musical notation. On the staff the shapes change location in relation to the key. Each shape represents movement around the tonic note. The system I saw every Sunday in the Christian Hymnal was a seven shape system. The shapes could be called: do, re, mi, fa, so, la, ti. So once you determine the key the tonic note becomes do.
For the song above, which is in the key of A, the shapes are translated like this:
That’s one less mystery in life.