John and Mary are both "Bible" names. This has a lot to do with why they are so common. Other names like Paul, Peter, Daniel, Michael, and Anne to name a few are also very common for this same reason.
Elizabeth, Catherine, Mary, Jane, John, George, Samuel, Benjamin, Thomas
Most of the names at that time were taken from the bible so names like John or Joseph were common names. Many people think Mary was in common use, but this is misguided, the name Mary became common only in the very late 1400s because it was considered too holy for normal use before that. Some names used for boys and girls are: Boys Richard Henry John Joseph Girls Elizabeth Alicia
Mary-Jane Mary-Lue Dorthy
Michael and Matthew are common boy names. Mary and Margaret are common girl names.
their names were elizabeth Mary and esther
John and Mary Grayson
William Shakespeare's parents names are Mary and John Shakespeare
If the names are like, "John Smith -and- Mary Smith", then they both have to sign the title. If the names are like, "John Smith -or- Mary Smith", then one signature is needed, and it can be by either one.
they're all stupid names
He was the son of the Reverend John Hancock and Mary Hawke Thaxter
John Steinbeck had three sister, Mary, Beth and Esther.
The letter 'a'.