“(T)he true key for the construction of everything doubtful in a law is the intention of the law-makers.  This is most safely gathered from the words, but may be sought also in the extraneous circumstances provided they do not contradict the express words of the law. – Thomas Jefferson (1808)

Further insights on the interpretation of the Constitution may be found here:

http://famguardian.org/Subjects/Politics/ThomasJefferson/jeff1020.htm