Crack open a traditional hymnal and most American Protestants will be able to belt out the classic hymn, "Holy, holy, holy! Lord God Almighty!"

The last verse states: "Holy, holy, holy! Lord God Almighty! All thy works shall praise thy name, in earth and sky and sea. Holy, holy, holy! Merciful and mighty, God in three persons, blessed Trinity."

Also, most practicing Catholics will be familiar with these Catechism lines: "The mystery of the Most Holy Trinity is the central mystery of Christian faith and life. It is the mystery of God in himself. ... The Trinity is One. We do not confess three Gods, but one God in three persons, the 'consubstantial Trinity'."

The language is mysterious and ancient. Yet according to a new survey probing what Americans believe on crucial theological issues, a majority of those polled -- 71 percent -- believe in the Trinity.

But what about that whole "God in three persons" thing? Not so much.