Tallis and Byrd’s Cantiones sacrae (1575)

What did Tallis and Byrd mean to convey by their use of the word "argument" in their title, Cantiones, quae ab argumento sacrae vocantur ? Thomas Tallis's and William Byrd's Cantiones, quae ab argumento sacrae vocantur (songs, which by their argument are called sacred) of 1575 is one of the first sets of sacred music printed in England. It is widely recognized as a landmark achievement in English music history. Dedicated to Queen Elizabeth I to mark the seventeenth year of her reign, each compos