Here's another example of the lawmakers, during the making of the Constitution, assuming that the common law rules of construction applied to the Constitution.
During the Constitutional Convention, when discussing whether the legal term "ex post facto law" included both civil law and criminal law, delegate John Dickinson announced that he had consulted his Blackstone and found that the illegitimacy of ex post facto laws applied only in criminal cases.
Dickinson probably determined that the first two rules of construction - regarding the "usual and most known" meaning of a word and the "context" of the word - wouldn't enable a judge to ascertain the meaning of "ex post facto law."
Dickinson knew a judge would then apply the third rule which says,"as to the subject matter, words are always to be understood as having a regard thereto..."
Dickinson didn't consult Blackstone's Commentaries because Blackstone was the "subject matter." However, Blackstone's book is where Dickinson found what the "subject matter" (English statutes and judicial opinions) said about the subject of "ex post facto."
Blackstone's book made it easy for Dickinson to find what the statutes and judicial opinions said about the meaning of the term. Before Blackstone organized the English Law, one had to dig through hundreds of years of judicial opinions to find the law.
Here is what he may have found in Blackstone's Commentaries which convinced Dickinson that the term "related to criminal cases only."
There is still a more unreasonable method than this, which is called making of laws ex post facto; when after an action is committed, the legislator then for the first time declares it to have been a crime, and inflicts a punishment upon the person who has committed it; here it is impossible that the party could foresee that an action, innocent when it was done, should be afterwards converted to guilt by a subsequent law; he had therefore no cause to abstain from it; and all punishment for not abstaining must of consequence be cruel and unjust.
