Nora Rotter Tillman (dubbed "the final non-appealable authority in the Tillman household on all disputed points of usage") and Seth Barrett Tillman have produced a nice essay warning against the dangers of assuming that words used in the Constitution meant then what they mean to us now. Here's the opening of A Fragment on Shall and May:
Recently Professors Randy E. Barnett and Sotirios Barber, two commentators with very different views with regard to how the United States Constitution should be interpreted, have expressed the view that "words have not, for the most part, changed meaning [since 1787]. Most of the meanings [of the words of the Constitution] have not been changed." We suggest that the American English of the founding generation was a more capacious language than its modern successor and that which came into being after Noah Webster's publication of his grade school primer, A Grammatical Institute of the English Language, in 1783, and his Dictionary in 1806. As we explain more fully below, where a word once had multiple meanings, but only one variant is now remembered and understood, we may be seriously mistaken when we ascribe near certainty to our understanding of how a constitutional term was used.
As the title suggests, the Tillmans explore, by way of example, the extent to which there really was a difference between the words "shall" (which we think of as mandatory) and "may" (which we think of as permissive). The article is only eight pages, so you should go read it for yourself.
As a postscript, the thought is nagging at me that I've seen a similar suggestion made concerning the terms "shall" and "ought". Many early state constitutions used the term "ought" in the context of defining rights (in the form "the legislature ought to protect free speech"), whereas the corresponding provision in the federal constitution uses the term "shall" ("Congress shall make no law respecting, etc."). The point was (if I'm not imagining it) that "ought" may have had a mandatory connotation similar to "shall", in which case the state constitutional provisions were not merely precatory.