A medieval gesture riddle: 'to take VII from VIII and have VI left'

In the fourth-century Symphosius wrote a book, which contained one hundred riddles. He even provided the answers to all the riddles. For the majority of the riddles the answers are relatively easy to guess. However, there is one exception, riddle number 96, which reads as follows: "If you this marvel to believe will design, Hold eight upon your hand — I’ll make it plain, Take seven away, and yet will six remain". The answer for this riddle is: “To take VII from VIII and have VI left.” This answer is most perplexing and appears to challenge the very foundations of our knowledge of arithmetic. In the early medieval era it was thought to be interesting or significant enough to be repeated in another book of riddles written by Alcuin in the eighth century. The answer given by Alcuin, and earlier by Symphosius, appears to be more confusing than enlightening. They both state that this riddle is worked out on the hands, which suggests that it is solved through computus digitorum. It has been thought that this riddle is a mnemonic or even a clue to the lost method of calculation with the hands. Both of these seem to be unsatisfactory solutions to its meaning; yet it is a very intriguing riddle. This paper considers this intriguing riddle and proposes a different solution to it.