The most important differences are the following: The permissive use of "Selections of Psalms in place of the Psalms appointed for the day of the month."
"A Short History of the Book of Common Prayer"
William Reed Huntington
40, and was of the highest importance, for the provision of county and borough asylums, instead of being permissive, was made compulsory.
"Chapters in the History of the Insane in the British Isles"
Daniel Hack Tuke
May is simply permissive; can is potential.
"The English Language"
Robert Gordon Latham